Inflammatory Myopathy (Dermatomyositis/Polymyositis)

VERSION: 1.1 CREATED: January 30, 2026 REVISED: January 30, 2026 STATUS: Approved

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DIAGNOSIS: Inflammatory Myopathy (Dermatomyositis/Polymyositis)

ICD-10: G72.41 (Inclusion body myositis - note: excluded from this template scope but listed for differential), M33.10 (Other dermatomyositis, unspecified organ involvement), M33.20 (Polymyositis, unspecified organ involvement), M33.90 (Dermatopolymyositis, unspecified), M33.00 (Juvenile dermatomyositis), M33.92 (Dermatopolymyositis, unspecified with myopathy), M60.9 (Myositis, unspecified)

CPT CODES: 82550 (Creatine kinase (CK)), 80053 (CMP (BMP + LFTs)), 85025 (CBC with differential), 82085 (Aldolase), 85652 (ESR), 86140 (CRP), 83615 (LDH), 84450 (AST), 82947 (Blood glucose), 83036 (HbA1c), 81001 (Urinalysis with microscopy), 84443 (TSH), 83735 (Magnesium), 84100 (Phosphorus), 85610 (PT/INR), 86235 (Myositis-specific antibody panel (comprehensive)), 86038 (ANA), 86255 (Anti-dsDNA), 83874 (Myoglobin (serum)), 84484 (Troponin I (cardiac-specific)), 83880 (BNP/NT-proBNP), 82728 (Ferritin), 80074 (Hepatitis B surface antigen, anti-HBc), 87389 (HIV 1/2 antigen/antibody), 82306 (Vitamin D (25-OH)), 86334 (SPEP with immunofixation), 73721 (MRI thighs with and without contrast (bilateral)), 71046 (Chest X-ray (PA and lateral)), 71250 (CT chest high-resolution (HRCT) without contrast), 93000 (ECG (12-lead)), 93306 (Echocardiogram), 73221 (MRI pelvis and proximal upper extremities), 74177 (CT chest/abdomen/pelvis with contrast), 78816 (PET/CT (FDG)), 75561 (Cardiac MRI with contrast), 74220 (Barium swallow / Modified barium swallow), 91010 (Esophageal manometry), 77067 (Mammography and/or breast MRI), 45378 (Colonoscopy), 76856 (Pelvic ultrasound (female patients)), 84153 (PSA (male patients)), 93451 (Right heart catheterization), 96365 (Methylprednisolone IV (pulse therapy)), 36514 (Plasmapheresis (PLEX))

SYNONYMS: Inflammatory myopathy, dermatomyositis, DM, polymyositis, PM, immune-mediated necrotizing myopathy, IMNM, anti-synthetase syndrome, ASyS, autoimmune myopathy, idiopathic inflammatory myopathy, IIM, myositis, autoimmune myositis, inflammatory muscle disease

SCOPE: Evaluation and management of inflammatory myopathies including dermatomyositis, polymyositis, and immune-mediated necrotizing myopathy. Includes diagnosis, acute management, immunotherapy, interstitial lung disease (ILD) screening, malignancy screening, and disease-modifying therapy. Excludes inclusion body myositis (IBM -- separate plan), drug-induced myopathy, infectious myositis, and metabolic myopathies.

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PRIORITY KEY: STAT = Immediate | URGENT = Within hours | ROUTINE = Standard | EXT = Extended/atypical cases | - = Not applicable to this setting

═══════════════════════════════════════════════════════════════ SECTION A: ACTION ITEMS ═══════════════════════════════════════════════════════════════

1. LABORATORY WORKUP

1A. Essential/Core Labs

Test	ED	HOSP	OPD	ICU	Rationale	Target Finding
Creatine kinase (CK) (CPT 82550)	STAT	STAT	ROUTINE	STAT	Primary biomarker of muscle inflammation; typically elevated 10-50x ULN in PM/IMNM; may be normal or mildly elevated in DM (especially amyopathic DM)	Normal (30-200 U/L); expect markedly elevated in active disease
CMP (BMP + LFTs) (CPT 80053)	STAT	STAT	ROUTINE	STAT	Renal function (rhabdomyolysis risk); hepatic function baseline for immunotherapy; AST/ALT often elevated from muscle (not liver)	Normal; expect elevated AST/ALT (muscle source)
CBC with differential (CPT 85025)	STAT	STAT	ROUTINE	STAT	Baseline before immunotherapy; infection screen; lymphopenia may suggest DM/anti-MDA5	Normal
Aldolase (CPT 82085)	URGENT	URGENT	ROUTINE	URGENT	Elevated in inflammatory myopathies; may be elevated when CK is normal (especially in DM)	Normal (<7.7 U/L); expect elevated in active disease
ESR (CPT 85652)	URGENT	ROUTINE	ROUTINE	URGENT	Inflammatory marker; often modestly elevated	Normal; mild-moderate elevation expected
CRP (CPT 86140)	URGENT	ROUTINE	ROUTINE	URGENT	Inflammatory marker; infection screen	Normal; mild-moderate elevation expected
LDH (CPT 83615)	URGENT	ROUTINE	ROUTINE	URGENT	Muscle enzyme marker; elevated in active myositis; also marker for ILD severity with anti-MDA5	Normal; elevated in active disease
AST (CPT 84450) / ALT (CPT 84460)	STAT	STAT	ROUTINE	STAT	Often elevated from skeletal muscle (not hepatic) -- correlate with CK; baseline before methotrexate/azathioprine	Normal; expect elevated (muscle source)
Blood glucose (CPT 82947)	STAT	STAT	ROUTINE	STAT	Pre-steroid baseline	Normal
HbA1c (CPT 83036)	-	ROUTINE	ROUTINE	-	Glycemic status before corticosteroid initiation	<5.7%
Urinalysis with microscopy (CPT 81001)	STAT	STAT	ROUTINE	STAT	Myoglobinuria screen (rhabdomyolysis); baseline	No myoglobin; no casts
TSH (CPT 84443)	URGENT	ROUTINE	ROUTINE	URGENT	Hypothyroid myopathy in differential; autoimmune thyroid overlap	Normal
Magnesium (CPT 83735)	STAT	STAT	ROUTINE	STAT	Baseline electrolyte; hypomagnesemia worsens weakness	Normal (1.7-2.2 mg/dL)
Phosphorus (CPT 84100)	STAT	STAT	ROUTINE	STAT	Hypophosphatemia causes weakness (mimic)	Normal (2.5-4.5 mg/dL)
PT/INR (CPT 85610), aPTT (CPT 85730)	STAT	ROUTINE	-	STAT	Coagulation baseline before procedures (muscle biopsy)	Normal
Pregnancy test (beta-hCG)	STAT	STAT	ROUTINE	STAT	Affects imaging and immunotherapy choices; methotrexate and mycophenolate contraindicated	Document result

1B. Extended Workup (Second-line)

Test	ED	HOSP	OPD	ICU	Rationale	Target Finding
Myositis-specific antibody panel (comprehensive) (CPT 86235)	-	URGENT	ROUTINE	URGENT	Identifies subtype and guides management: anti-Jo-1 (ASyS), anti-Mi-2 (classic DM, good prognosis), anti-MDA5 (amyopathic DM, rapidly progressive ILD), anti-NXP2 (calcinosis, malignancy), anti-TIF1-gamma (malignancy association), anti-SRP (necrotizing myopathy, severe), anti-HMGCR (necrotizing myopathy, statin-associated)	Negative; positive result defines clinical phenotype
Anti-Jo-1 antibody (CPT 86235)	-	URGENT	ROUTINE	URGENT	Most common anti-synthetase antibody (20-30% of myositis); anti-synthetase syndrome: myositis + ILD + mechanic's hands + arthritis + Raynaud + fever	Negative
Anti-Mi-2 antibody	-	ROUTINE	ROUTINE	-	Classic dermatomyositis phenotype (heliotrope rash, Gottron papules); generally good prognosis and steroid-responsive	Negative
Anti-MDA5 (anti-CADM-140) antibody	-	URGENT	ROUTINE	URGENT	Clinically amyopathic DM with rapidly progressive ILD (high mortality); skin ulcers; palmar papules; ferritin often markedly elevated	Negative; positive requires URGENT ILD evaluation
Anti-NXP2 (anti-MJ) antibody	-	ROUTINE	ROUTINE	-	Associated with calcinosis (especially juvenile DM); adult-onset associated with malignancy risk	Negative
Anti-TIF1-gamma (anti-p155/140) antibody	-	URGENT	ROUTINE	URGENT	Strongly associated with malignancy in adult-onset DM (up to 60% cancer risk); requires comprehensive malignancy screening	Negative; positive mandates cancer screening
Anti-SRP (signal recognition particle) antibody	-	URGENT	ROUTINE	URGENT	Immune-mediated necrotizing myopathy (IMNM); severe proximal weakness; very high CK; poor response to steroids alone; cardiac involvement risk	Negative
Anti-HMGCR antibody	-	URGENT	ROUTINE	URGENT	Immune-mediated necrotizing myopathy (IMNM); often statin-associated but can occur without statin exposure; very high CK; requires aggressive immunotherapy	Negative
Anti-PL-7 antibody	-	ROUTINE	ROUTINE	-	Anti-synthetase antibody; ILD risk; arthritis; mechanic's hands	Negative
Anti-PL-12 antibody	-	ROUTINE	ROUTINE	-	Anti-synthetase antibody; ILD-predominant phenotype	Negative
Anti-EJ antibody	-	ROUTINE	ROUTINE	-	Anti-synthetase antibody; ILD risk	Negative
Anti-OJ antibody	-	ROUTINE	ROUTINE	-	Anti-synthetase antibody; ILD risk	Negative
Anti-SAE antibody	-	ROUTINE	ROUTINE	-	Dermatomyositis-specific; dysphagia common; may initially present with skin-only disease then develop myopathy	Negative
ANA (CPT 86038)	-	ROUTINE	ROUTINE	-	Positive in 60-80% of inflammatory myopathy; connective tissue disease overlap screen	Negative or low titer
Anti-dsDNA (CPT 86255)	-	ROUTINE	ROUTINE	-	SLE overlap syndrome screen	Negative
Anti-SSA/Ro, Anti-SSB/La	-	ROUTINE	ROUTINE	-	Sjogren overlap; neonatal lupus risk if positive in pregnancy	Negative
Anti-U1 RNP	-	ROUTINE	ROUTINE	-	Mixed connective tissue disease overlap (myositis + Raynaud + swollen hands + ILD)	Negative
Anti-Scl-70 (anti-topoisomerase I)	-	ROUTINE	ROUTINE	-	Scleroderma overlap myositis	Negative
Myoglobin (serum) (CPT 83874)	STAT	STAT	-	STAT	Rhabdomyolysis assessment in acute severe myositis (CK >10,000)	Normal; elevated in rhabdomyolysis
Myoglobin (urine)	STAT	STAT	-	STAT	Myoglobinuria detection in rhabdomyolysis	Negative
Troponin I (cardiac-specific) (CPT 84484)	STAT	STAT	-	STAT	Cardiac involvement screening (myocarditis risk especially with anti-SRP); do NOT use troponin T (cross-reacts with skeletal muscle)	Normal; elevated suggests cardiac involvement
BNP/NT-proBNP (CPT 83880)	URGENT	ROUTINE	ROUTINE	URGENT	Heart failure screen; pulmonary hypertension from ILD	Normal
Ferritin (CPT 82728)	URGENT	URGENT	ROUTINE	URGENT	Markedly elevated (>1500 ng/mL) in anti-MDA5 with rapidly progressive ILD; also macrophage activation syndrome marker	Normal; markedly elevated in anti-MDA5 ILD
Hepatitis B surface antigen, anti-HBc (CPT 80074)	-	ROUTINE	ROUTINE	-	Screen before rituximab/immunosuppression (reactivation risk)	Negative
Hepatitis C antibody (CPT 80074)	-	ROUTINE	ROUTINE	-	Screen before immunosuppression; HCV-associated myositis in differential	Negative
HIV 1/2 antigen/antibody (CPT 87389)	-	ROUTINE	ROUTINE	-	HIV-associated myopathy in differential; screen before immunosuppression	Negative
Vitamin D (25-OH) (CPT 82306)	-	ROUTINE	ROUTINE	-	Deficiency common; steroid-induced osteoporosis prevention; immune modulation	>30 ng/mL
Quantitative immunoglobulins (IgG, IgA, IgM)	-	ROUTINE	ROUTINE	-	Baseline before IVIG/rituximab; monitor on immunosuppression	Normal
TB test (QuantiFERON-Gold or PPD)	-	ROUTINE	ROUTINE	-	Screen before immunosuppression	Negative

1C. Rare/Specialized (Refractory or Atypical)

Test	ED	HOSP	OPD	ICU	Rationale	Target Finding
Anti-cN1A (anti-NT5C1A) antibody	-	EXT	EXT	-	Inclusion body myositis marker; if clinical features suggest IBM (distal weakness, finger flexor/quad weakness, refractory to immunotherapy)	Negative (positive suggests IBM)
Paraneoplastic antibody panel (serum) (CPT 86255)	-	EXT	EXT	-	Paraneoplastic myopathy screen if malignancy workup negative but clinical suspicion high	Negative
Anti-HMGCR antibody (if not in initial panel)	-	EXT	ROUTINE	-	If statin exposure history and necrotizing myopathy pattern on biopsy	Negative
Complement C3, C4 (CPT 86160, 86161)	-	ROUTINE	ROUTINE	-	Baseline before complement-modulating therapy; SLE overlap	Normal
SPEP with immunofixation (CPT 86334)	-	ROUTINE	EXT	-	Paraproteinemia screen; some myopathies associated with monoclonal gammopathy	Normal
Anti-PM-Scl antibody	-	EXT	EXT	-	Overlap myositis-scleroderma phenotype	Negative
Anti-Ku antibody	-	EXT	EXT	-	Overlap syndrome (SLE/scleroderma/myositis)	Negative
Muscle enzyme panel: AST, ALT, LDH, aldolase, CK (serial)	-	ROUTINE	ROUTINE	ROUTINE	Trending response to immunotherapy; all may be elevated from muscle source	Declining toward normal with treatment
IL-18 level	-	EXT	EXT	-	Markedly elevated in anti-MDA5 rapidly progressive ILD; prognostic marker	Normal
KL-6 (Krebs von den Lungen-6)	-	EXT	EXT	-	ILD biomarker; elevated in active ILD; may guide treatment response	Normal
Genetic testing (hereditary myopathy panel)	-	-	EXT	-	If inflammatory myopathy treatment-refractory and biopsy atypical; consider limb-girdle muscular dystrophy, dysferlinopathy (which can mimic PM)	Normal

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2. DIAGNOSTIC IMAGING & STUDIES

2A. Essential/First-line

Study	ED	HOSP	OPD	ICU	Timing	Target Finding	Contraindications
MRI thighs with and without contrast (bilateral) (CPT 73721)	-	URGENT	ROUTINE	-	Within first week of evaluation; guides biopsy site	Muscle edema (T2/STIR hyperintensity) indicating active inflammation; fatty infiltration indicating chronic damage; patterns help distinguish DM vs PM vs IMNM	Pacemaker, metallic implants, severe claustrophobia, GFR <30 (gadolinium)
Chest X-ray (PA and lateral) (CPT 71046)	URGENT	ROUTINE	ROUTINE	URGENT	At presentation	Interstitial lung disease screening; aspiration pneumonia; baseline	None significant
CT chest high-resolution (HRCT) without contrast (CPT 71250)	URGENT	URGENT	ROUTINE	URGENT	Within 1-2 weeks of diagnosis; URGENT if anti-MDA5, anti-Jo-1, or respiratory symptoms	ILD pattern: NSIP (most common), UIP, organizing pneumonia, DAD (anti-MDA5); ground-glass opacities; basilar predominant	Pregnancy (relative)
ECG (12-lead) (CPT 93000)	URGENT	ROUTINE	ROUTINE	URGENT	At presentation	Conduction abnormalities; arrhythmias (myocarditis screen, especially anti-SRP)	None
Pulmonary function tests (PFTs) with DLCO (CPT 94010, 94729)	-	ROUTINE	ROUTINE	-	Within first 2 weeks of diagnosis; baseline for ILD monitoring	FVC >80% predicted; DLCO >80% predicted; restrictive pattern suggests ILD or respiratory muscle weakness	Unable to cooperate; active pneumothorax
Echocardiogram (CPT 93306)	-	ROUTINE	ROUTINE	URGENT	Within first 2 weeks; URGENT if cardiac symptoms or anti-SRP positive	Normal LV/RV function; no pericardial effusion; PASP <35 mmHg (screen for pulmonary HTN from ILD)	None significant

2B. Extended

Study	ED	HOSP	OPD	ICU	Timing	Target Finding	Contraindications
EMG/NCS (CPT 95886, 95907-95913)	-	URGENT	ROUTINE	-	During initial workup; helps confirm myopathic process and guide biopsy	Myopathic pattern: short-duration, low-amplitude, polyphasic MUAPs; fibrillations and positive sharp waves (active inflammation); increased insertional activity; normal NCS (unless overlap neuropathy)	None significant; avoid anticoagulated limbs for needle EMG
MRI pelvis and proximal upper extremities (CPT 73221)	-	ROUTINE	ROUTINE	-	If thigh MRI insufficient or upper extremity involvement prominent	Muscle edema pattern; guide biopsy site; assess disease extent	Pacemaker, metallic implants, severe claustrophobia, GFR <30 (gadolinium)
CT chest/abdomen/pelvis with contrast (CPT 74177)	-	ROUTINE	ROUTINE	-	Within 1 month of diagnosis for malignancy screening; URGENT if anti-TIF1-gamma positive	No occult malignancy	Contrast allergy; renal insufficiency
PET/CT (FDG) (CPT 78816)	-	ROUTINE	ROUTINE	-	If anti-TIF1-gamma positive or age >40 with DM; comprehensive malignancy screen	No FDG-avid malignancy; may also show active myositis	Uncontrolled diabetes (affects FDG uptake); pregnancy
Cardiac MRI with contrast (CPT 75561)	-	ROUTINE	ROUTINE	-	If troponin elevated or echocardiogram abnormal; especially with anti-SRP	No myocarditis; no late gadolinium enhancement	Pacemaker; GFR <30
Whole-body MRI (WB-MRI)	-	EXT	EXT	-	Comprehensive assessment of muscle involvement if considering multiple biopsy sites	Map of active inflammation vs chronic damage across all muscle groups	Pacemaker, metallic implants, severe claustrophobia, GFR <30 (gadolinium)
Barium swallow / Modified barium swallow (CPT 74220)	-	ROUTINE	ROUTINE	-	If dysphagia present; cricopharyngeal involvement common in inflammatory myopathy	Normal swallow mechanics; no aspiration; no cricopharyngeal bar	None significant
Esophageal manometry (CPT 91010)	-	EXT	ROUTINE	-	If dysphagia without structural cause; proximal esophageal dysmotility	Normal esophageal motility; abnormal proximal striated muscle segment suggests myositis	Unable to cooperate

2C. Rare/Specialized

Study	ED	HOSP	OPD	ICU	Timing	Target Finding	Contraindications
Muscle biopsy (open or needle) (CPT 20200, 20206)	-	ROUTINE	ROUTINE	-	After MRI guidance; within 2-4 weeks of diagnosis; biopsy inflamed (not fatty) muscle; avoid recently EMG'd muscle on ipsilateral side	DM: perifascicular atrophy, perivascular inflammation (CD4+/B cells), MAC deposition on capillaries. PM: endomysial inflammation with CD8+ T-cell invasion of non-necrotic fibers. IMNM: necrotic and regenerating fibers with minimal inflammation, MAC deposition on muscle fibers	Coagulopathy; anticoagulation (hold); infection at site
Skin biopsy (if DM rash atypical)	-	ROUTINE	ROUTINE	-	If DM rash uncertain; distinguish from SLE, psoriasis, eczema	Interface dermatitis; mucin deposition; perivascular lymphocytic infiltrate	Infection at site
Mammography and/or breast MRI (CPT 77067)	-	ROUTINE	ROUTINE	-	Malignancy screening in DM (especially anti-TIF1-gamma); age-appropriate or if DM diagnosed	No malignancy	Pregnancy (for mammography; MRI alternative)
Colonoscopy (CPT 45378)	-	ROUTINE	ROUTINE	-	Malignancy screening if anti-TIF1-gamma positive or age >50 with any DM/PM	No malignancy	Active GI bleeding; bowel perforation
Pelvic ultrasound (female patients) (CPT 76856)	-	ROUTINE	ROUTINE	-	Ovarian cancer screening in female DM patients (especially anti-TIF1-gamma)	No ovarian mass	None significant
PSA (male patients) (CPT 84153)	-	ROUTINE	ROUTINE	-	Prostate cancer screening in male DM patients	Normal (<4 ng/mL)	None
Nailfold capillaroscopy	-	ROUTINE	ROUTINE	-	DM-specific microvascular assessment; correlates with disease activity; enlarged capillaries, dropout, hemorrhages	Normal capillary architecture	None
Right heart catheterization (CPT 93451)	-	EXT	EXT	EXT	If echocardiogram suggests pulmonary hypertension (PASP >40); especially with chronic ILD	mPAP <20 mmHg	Coagulopathy; active infection

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3. TREATMENT

3A. Acute/Emergent

Treatment	Route	Indication	Dosing	Contraindications	Monitoring	ED	HOSP	OPD	ICU
Methylprednisolone IV (pulse therapy) (CPT 96365)	IV	Severe active myositis; rapidly progressive ILD (anti-MDA5); dysphagia with aspiration risk; respiratory failure from ILD	1000 mg :: IV :: daily x 3-5 days :: 1000 mg IV daily for 3-5 days; infuse over 60-90 min; followed by oral prednisone taper	Active untreated infection; uncontrolled diabetes; psychosis; GI bleeding	Glucose q6h (target <180); BP; mood/sleep; cardiac monitoring during infusion; GI prophylaxis	STAT	STAT	-	STAT
Prednisone (high-dose oral)	PO	Active inflammatory myopathy; transition from IV pulse therapy	1 mg/kg :: PO :: daily :: 1 mg/kg/day (max 80 mg) as single morning dose; maintain 4-8 weeks until CK normalizes and strength improves, then taper	Active untreated infection; uncontrolled diabetes; psychosis	Glucose, BP, weight, mood weekly inpatient; bone density baseline; GI prophylaxis	-	STAT	ROUTINE	STAT
IVIG (intravenous immunoglobulin) (CPT 96365)	IV	Moderate-severe DM (ProDERM trial); dysphagia; steroid-refractory myositis; bridge therapy during steroid-sparing agent onset	2 g/kg :: IV :: over 2-5 days :: 2 g/kg total divided over 2-5 days (e.g., 0.4 g/kg/day x 5 days); then 2 g/kg every 4 weeks as maintenance; start infusion slow and increase per protocol	IgA deficiency (use IgA-depleted product); acute renal failure; recent thrombotic event	Vital signs q15min during first infusion; renal function (BUN, Cr); headache (aseptic meningitis); thrombotic events; hemolysis (haptoglobin, LDH, direct Coombs)	-	STAT	ROUTINE	STAT
Plasmapheresis (PLEX) (CPT 36514)	Extracorporeal	Severe/refractory myositis not responding to steroids/IVIG; anti-SRP IMNM; acute respiratory failure from ILD	5 exchanges :: Extracorporeal :: every other day x 10-14 days :: 5 exchanges over 10-14 days (every other day); each exchange 1-1.5 plasma volumes; albumin replacement	Hemodynamic instability; sepsis; active bleeding; poor vascular access	BP continuous during exchange; calcium (citrate toxicity); fibrinogen; CBC; electrolytes; line infection	-	URGENT	-	URGENT
Omeprazole (GI prophylaxis during steroids)	PO	GI protection during high-dose corticosteroids	20-40 mg :: PO :: daily :: 20-40 mg PO daily while on steroids	PPI allergy	None routine	STAT	STAT	ROUTINE	STAT
Insulin sliding scale (steroid-induced hyperglycemia)	SC	Glucose management during high-dose steroids	Per protocol :: SC :: PRN glucose >180 :: Per institutional sliding scale protocol if glucose >180 mg/dL	Hypoglycemia risk	Glucose q6h minimum during pulse steroids	STAT	STAT	-	STAT
DVT prophylaxis: Enoxaparin	SC	VTE prevention in immobilized patients with myositis	40 mg :: SC :: daily :: 40 mg SC daily; start on admission	Active bleeding; platelets <50K; CrCl <30 (use UFH)	Platelets q3 days; anti-Xa if renal impairment	-	ROUTINE	-	ROUTINE
DVT prophylaxis: Heparin SC (alternative)	SC	VTE prevention if enoxaparin contraindicated	5000 units :: SC :: q8-12h :: 5000 units SC q8-12h	Active bleeding; HIT history	Platelets q3 days	-	ROUTINE	-	ROUTINE
Aggressive IV hydration (rhabdomyolysis)	IV	Rhabdomyolysis prevention/treatment if CK >10,000; myoglobinuria	200-300 mL/h NS :: IV :: continuous :: 200-300 mL/hr normal saline; target urine output >200 mL/h; consider sodium bicarbonate drip to alkalinize urine (target pH >6.5)	Heart failure; volume overload	Urine output hourly; serum CK q6-12h; electrolytes q6h (hyperkalemia risk); renal function; urine pH	STAT	STAT	-	STAT

3B. Symptomatic Treatments

Treatment	Route	Indication	Dosing	Contraindications	Monitoring	ED	HOSP	OPD	ICU
Acetaminophen	PO	Myalgia and arthralgia pain relief	650-1000 mg :: PO :: q6h PRN :: 650-1000 mg PO q6h PRN; max 4 g/day (2 g if hepatic impairment)	Severe liver disease	LFTs if prolonged use	STAT	ROUTINE	ROUTINE	STAT
Ibuprofen	PO	Arthralgia (anti-synthetase syndrome); mild myalgia	400-600 mg :: PO :: q6-8h PRN :: 400-600 mg PO q6-8h PRN with food; max 2400 mg/day; use lowest effective dose for shortest duration	Active GI bleeding; renal impairment; concurrent anticoagulation	Renal function; GI symptoms	-	ROUTINE	ROUTINE	-
Hydroxychloroquine (Plaquenil)	PO	DM skin disease (rash, photosensitivity); anti-synthetase syndrome arthritis; adjunctive immunomodulation	200 mg :: PO :: BID :: 200 mg PO BID (max 5 mg/kg/day based on actual body weight); onset 2-3 months for skin benefit	Retinal disease; G6PD deficiency; QTc prolongation	Baseline ophthalmologic exam; annual retinal screening after 5 years (or 1 year if high risk); ECG baseline	-	ROUTINE	ROUTINE	-
Sunscreen and sun protection	TOP	DM skin disease management; photosensitivity is hallmark of DM	SPF 50+ :: TOP :: daily :: Apply broad-spectrum SPF 50+ to all exposed areas daily; reapply q2h with sun exposure; photoprotective clothing	None	Skin exam; rash activity	-	ROUTINE	ROUTINE	-
Topical corticosteroid (triamcinolone 0.1%)	TOP	DM skin rash (Gottron papules, heliotrope, V-sign, shawl sign)	Thin layer :: TOP :: BID :: Apply thin layer to affected skin BID; avoid face for prolonged use (use hydrocortisone 1% or tacrolimus on face)	Skin infection at site; skin atrophy	Skin atrophy; telangiectasia; infection	-	ROUTINE	ROUTINE	-
Topical tacrolimus 0.1% (Protopic)	TOP	DM facial rash (heliotrope rash); steroid-sparing for facial skin	Thin layer :: TOP :: BID :: Apply thin layer to affected facial skin BID; onset 2-4 weeks	Skin infection; immunosuppression concern	Burning sensation (transient); skin infection	-	ROUTINE	ROUTINE	-
Calcium carbonate + Vitamin D (bone protection)	PO	Osteoporosis prevention during chronic corticosteroid therapy	1000-1200 mg Ca + 1000-2000 IU D :: PO :: daily :: Calcium 1000-1200 mg + Vitamin D 1000-2000 IU PO daily while on chronic steroids	Hypercalcemia; hyperparathyroidism	Serum calcium; vitamin D level; DEXA if steroids >3 months	-	ROUTINE	ROUTINE	-
Alendronate (bone protection)	PO	Osteoporosis prevention if chronic steroids anticipated >3 months	70 mg :: PO :: weekly :: 70 mg PO weekly on empty stomach; remain upright 30 min after	GFR <35; esophageal disorders; inability to remain upright 30 min	DEXA at baseline and q2 years; renal function; dental exam (ONJ risk)	-	-	ROUTINE	-
Trimethoprim-sulfamethoxazole (PCP prophylaxis)	PO	PCP prevention if prednisone >=20 mg for >=4 weeks or concurrent immunosuppressants	1 DS tablet (160/800 mg) :: PO :: daily or 3x/week :: 1 DS tablet (160/800 mg) PO daily or 3 times per week	Sulfonamide allergy; severe renal impairment	CBC; renal function; use dapsone or atovaquone if allergic	-	ROUTINE	ROUTINE	-
Docusate sodium	PO	Constipation (immobility + opioid use)	100 mg :: PO :: BID :: 100 mg PO BID	GI obstruction	Bowel function	-	ROUTINE	ROUTINE	-
Melatonin	PO	Insomnia (steroid-induced)	3-5 mg :: PO :: qHS :: 3-5 mg PO qHS	None significant	Sleep quality	-	ROUTINE	ROUTINE	-
Gabapentin	PO	Neuropathic pain or myalgia not responsive to simple analgesics	300 mg :: PO :: qHS :: Start 300 mg PO qHS; increase by 300 mg/day every 1-3 days; target 900-1800 mg TID; max 3600 mg/day	Severe renal impairment (dose adjust)	Sedation, dizziness; renal function	-	ROUTINE	ROUTINE	-

3C. Second-line/Refractory

Treatment	Route	Indication	Dosing	Contraindications	Monitoring	ED	HOSP	OPD	ICU
Rituximab (Rituxan) (CPT 96365)	IV	Refractory DM/PM not responding to conventional immunosuppressants; anti-SRP IMNM; anti-synthetase syndrome refractory to first-line	375 mg/m2 or 1000 mg :: IV :: weekly x 4 or 2 doses 14 days apart :: 375 mg/m2 IV weekly x 4 weeks; OR 1000 mg IV x 2 doses 14 days apart; re-dose based on CD19/CD20 recovery and clinical response; onset 3-6 months	Active hepatitis B; active severe infection; severe immunodeficiency	HBV serology before; CD19/CD20 counts q3-6 months; immunoglobulins q6 months; PML risk (very rare); premedicate with acetaminophen, diphenhydramine, methylprednisolone	-	ROUTINE	ROUTINE	-
Tofacitinib (Xeljanz)	PO	Refractory DM (especially skin disease); anti-MDA5 DM with ILD (emerging evidence); refractory anti-synthetase syndrome	5 mg :: PO :: BID :: 5 mg PO BID; may increase to 11 mg daily (XR formulation); onset 1-3 months	Active serious infection; lymphopenia <500; current or history of DVT/PE (FDA black box); malignancy history	CBC q4-8 weeks; lipids at 4-8 weeks; LFTs; renal function; infection screen; VTE risk assessment; TB screening	-	EXT	ROUTINE	-
Ruxolitinib (Jakafi)	PO	Refractory DM skin disease; refractory anti-MDA5 ILD (emerging evidence)	5 mg :: PO :: BID :: Start 5 mg PO BID; may increase to 10 mg BID based on response and tolerability	Severe hepatic impairment; severe renal impairment; concurrent strong CYP3A4 inhibitors (reduce dose)	CBC weekly x 4 weeks then q2-4 weeks; lipids; LFTs; infection; VTE risk	-	EXT	EXT	-
Calcineurin inhibitor: Tacrolimus (rescue for anti-MDA5 ILD)	PO	Anti-MDA5 rapidly progressive ILD (combined with steroids and cyclophosphamide as triple therapy)	1 mg :: PO :: BID :: Start 1 mg PO BID; titrate to trough level 5-10 ng/mL; onset 2-4 weeks; used in Japanese triple-therapy protocol	Uncontrolled hypertension; renal impairment	Trough levels q1-2 weeks during titration; renal function; electrolytes (K, Mg); glucose; BP; tremor; nephrotoxicity	-	URGENT	ROUTINE	URGENT
Cyclophosphamide (CPT 96365)	IV	Rapidly progressive ILD (especially anti-MDA5); severe refractory myositis; anti-synthetase syndrome with progressive ILD	500-1000 mg/m2 :: IV :: monthly x 6 months :: IV pulse: 500-1000 mg/m2 monthly x 6 months; OR low-dose Euro-Lupus protocol: 500 mg IV every 2 weeks x 6 doses; MESNA prophylaxis with each dose	Pregnancy; active infection; bone marrow suppression; hemorrhagic cystitis	CBC weekly; urinalysis (hemorrhagic cystitis); fertility counseling; malignancy risk; MESNA with IV dosing; aggressive hydration	-	URGENT	EXT	URGENT
Combination therapy for anti-MDA5 ILD: Methylprednisolone + Tacrolimus + Cyclophosphamide	IV/PO	Rapidly progressive ILD with anti-MDA5 antibody (Tsuji triple-therapy protocol; high mortality without aggressive treatment)	Methylpred 1000 mg IV x 3d + tacrolimus 1 mg BID + CYC 500-750 mg/m2 :: IV/PO :: per protocol :: Pulse methylprednisolone 1000 mg IV x 3 days then prednisone 1 mg/kg + tacrolimus (trough 5-10 ng/mL) + IV cyclophosphamide 500-750 mg/m2 monthly; early combination improves survival	Active untreated infection; pregnancy; bone marrow suppression; hemorrhagic cystitis; uncontrolled diabetes; uncontrolled hypertension; renal impairment	Glucose q6h during pulse steroids; tacrolimus trough q1-2 weeks; CBC weekly; urinalysis (hemorrhagic cystitis); renal function; electrolytes; BP; combined immunosuppression toxicity; infection prophylaxis critical	-	STAT	-	STAT
Second course IVIG	IV	DM/PM with incomplete response to initial IVIG course; relapse during taper	2 g/kg :: IV :: over 2-5 days :: 2 g/kg total divided over 2-5 days; repeat q4 weeks as maintenance	IgA deficiency (use IgA-depleted product); acute renal failure; recent thrombotic event	Vital signs q15min during infusion; renal function (BUN, Cr); headache (aseptic meningitis); thrombotic events; hemolysis (haptoglobin, LDH, direct Coombs)	-	URGENT	ROUTINE	URGENT

3D. Disease-Modifying or Chronic Therapies

Treatment	Route	Indication	Dosing	Pre-Treatment Requirements	Contraindications	Monitoring	ED	HOSP	OPD	ICU
Methotrexate	PO/SC	First-line steroid-sparing agent for PM and DM; anti-synthetase syndrome arthritis; onset 3-6 months	10-15 mg :: PO/SC :: weekly :: Start 10-15 mg PO/SC once weekly; increase by 5 mg every 4 weeks to target 20-25 mg/week; folic acid 1 mg PO daily (except methotrexate day) mandatory	CBC, LFTs, renal function, hepatitis B/C serology, chest X-ray; TB screening	Pregnancy (Category X); hepatic disease; renal impairment (CrCl <30); active infection; pulmonary fibrosis (caution -- methotrexate pneumonitis vs ILD); concurrent TMP-SMX (increases toxicity)	CBC q2-4 weeks during titration then q8-12 weeks; LFTs q8-12 weeks; renal function; pulmonary symptoms (methotrexate pneumonitis); folic acid compliance	-	ROUTINE	ROUTINE	-
Azathioprine (Imuran)	PO	Steroid-sparing agent for PM and DM; maintenance therapy; onset 6-12 months	50 mg :: PO :: daily :: Start 50 mg PO daily; increase by 50 mg every 1-2 weeks to target 2-3 mg/kg/day (typically 150-250 mg/day)	TPMT genotype/activity BEFORE starting (mandatory); CBC; LFTs; hepatitis B/C serology; TB screening	TPMT deficiency (homozygous); concurrent allopurinol (reduce azathioprine dose by 75%); pregnancy (relative -- discuss risk/benefit)	TPMT before starting; CBC q1-2 weeks during titration then monthly; LFTs q4-8 weeks; lymphocyte count target 600-1000; amylase/lipase if abdominal pain	-	ROUTINE	ROUTINE	-
Mycophenolate mofetil (CellCept)	PO	Steroid-sparing agent for DM and PM; ILD associated with anti-synthetase syndrome; onset 3-6 months	500 mg :: PO :: BID :: Start 500 mg PO BID; increase to 1000 mg BID after 2 weeks; target 2000-3000 mg/day in divided doses	CBC, LFTs, renal function; hepatitis B/C serology; TB screening; pregnancy test (females)	Pregnancy (Category D -- teratogenic); concurrent azathioprine; active infection	CBC q2 weeks x 3 months then monthly; LFTs; GI side effects (diarrhea, nausea); lymphopenia; REMS pregnancy prevention	-	ROUTINE	ROUTINE	-
Tacrolimus	PO	Steroid-sparing agent; particularly effective for anti-synthetase syndrome and ILD; faster onset than azathioprine/mycophenolate (2-3 months)	1 mg :: PO :: BID :: Start 1 mg PO BID; titrate to trough level 5-10 ng/mL; onset 2-3 months	CBC, LFTs, renal function; electrolytes; glucose; BP; hepatitis B/C serology	Uncontrolled hypertension; renal impairment; concurrent strong CYP3A4 inhibitors	Trough levels q1-2 weeks during titration then q1-3 months; renal function; electrolytes (K, Mg); glucose; BP; tremor; nephrotoxicity	-	-	ROUTINE	-
Prednisone (chronic taper)	PO	Long-term immunosuppression taper; target lowest effective dose with steroid-sparing agent	5-10 mg :: PO :: daily :: Once stable on target dose with steroid-sparing agent for 4-8 weeks: decrease by 5-10 mg every 2-4 weeks until 20 mg, then 2.5-5 mg monthly; target <10 mg daily or off; many patients require long-term low-dose (5-10 mg)	Stable on steroid-sparing agent at target dose for 4-8 weeks before initiating taper	Do NOT stop abruptly if >2 weeks of therapy; active infection	Adrenal insufficiency symptoms; disease flare; cortisol level if concerns about adrenal suppression	-	ROUTINE	ROUTINE	-
IVIG (maintenance)	IV	Maintenance immunomodulation for DM (FDA evidence from ProDERM); steroid-sparing; refractory disease	2 g/kg :: IV :: q4 weeks :: 2 g/kg IV divided over 2-5 days every 4 weeks; may reduce frequency to q6-8 weeks if stable	IgA level, renal function, CBC; hepatitis B serology	IgA deficiency; renal failure; recent thrombotic event	Pre-infusion renal function; vital signs during infusion; headache; thrombosis risk; renal function trending	-	ROUTINE	ROUTINE	-
Subcutaneous immunoglobulin (SCIg)	SC	Alternative to IVIG for maintenance; patient self-administration; fewer systemic side effects	Weight-based :: SC :: weekly :: Equivalent monthly dose to IVIG divided into weekly SC infusions; multiple sites simultaneously; onset immediate (conversion from IVIG)	IgA level; renal function; adequate SC tissue assessment	IgA deficiency (use IgA-depleted product); acute renal failure; recent thrombotic event; inadequate SC tissue	Local infusion site reactions; IgG trough levels; renal function; thrombotic events	-	-	ROUTINE	-

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4. OTHER RECOMMENDATIONS

4A. Referrals & Consults

Recommendation	ED	HOSP	OPD	ICU
Neurology/Neuromuscular specialist for diagnostic confirmation, antibody interpretation, and immunotherapy guidance	URGENT	URGENT	ROUTINE	URGENT
Rheumatology co-management for overlap connective tissue disease, shared immunotherapy decisions, and skin disease management	-	ROUTINE	ROUTINE	-
Pulmonology for ILD evaluation, PFT interpretation, and respiratory management (mandatory if anti-Jo-1, anti-MDA5, or any respiratory symptoms)	URGENT	URGENT	ROUTINE	URGENT
Dermatology for DM rash management, skin biopsy if needed, and photosensitivity counseling	-	ROUTINE	ROUTINE	-
Oncology referral for malignancy screening and management (mandatory if anti-TIF1-gamma positive or age >40 with new DM)	-	URGENT	ROUTINE	-
Speech-language pathology for swallow evaluation given dysphagia risk (cricopharyngeal and proximal esophageal involvement common in inflammatory myopathy)	URGENT	URGENT	ROUTINE	URGENT
Physical therapy for proximal weakness rehabilitation, fall prevention, and graded exercise program (avoid eccentric exercise during active inflammation)	-	ROUTINE	ROUTINE	-
Occupational therapy for ADL adaptation, energy conservation, and upper extremity function given proximal weakness	-	ROUTINE	ROUTINE	-
Cardiology if elevated troponin, arrhythmia, or anti-SRP antibody positive (myocarditis risk)	URGENT	URGENT	ROUTINE	URGENT
Gastroenterology for dysphagia evaluation (esophageal manometry, EGD) and malignancy screening (colonoscopy)	-	ROUTINE	ROUTINE	-
Gynecology for ovarian cancer screening in female DM patients (especially anti-TIF1-gamma positive)	-	ROUTINE	ROUTINE	-
Social work for disability evaluation, insurance navigation for biologic therapies, and community resources	-	ROUTINE	ROUTINE	-
Infusion center coordination for IVIG, rituximab, or cyclophosphamide infusion scheduling	-	ROUTINE	ROUTINE	-
Pain management if refractory myalgia or arthralgia not responding to standard analgesics and immunotherapy	-	-	EXT	-
Psychiatry/Psychology for adjustment to chronic illness, depression screening, and steroid-induced mood disturbance	-	ROUTINE	ROUTINE	-
Nutrition/Dietetics for dysphagia diet modification, weight management on steroids, and nutritional optimization for muscle recovery	-	ROUTINE	ROUTINE	-
Palliative care for severely refractory disease with significant symptom burden and goals of care discussion	-	-	EXT	-

4B. Patient Instructions

Recommendation	ED	HOSP	OPD
Return to ED immediately if worsening difficulty breathing or new shortness of breath (may indicate ILD progression or respiratory muscle failure)	STAT	STAT	ROUTINE
Return to ED if worsening difficulty swallowing, choking on food or liquids, or new voice changes (aspiration risk)	STAT	STAT	ROUTINE
Return to ED if dark brown or cola-colored urine (may indicate rhabdomyolysis requiring urgent IV fluids)	STAT	STAT	ROUTINE
Return to ED if new chest pain or palpitations (may indicate myocarditis or cardiac involvement)	STAT	STAT	ROUTINE
Report any new rash or worsening skin changes to neurology/rheumatology (may indicate disease flare or new DM diagnosis)	-	ROUTINE	ROUTINE
Do NOT stop prednisone or immunosuppressant abruptly (adrenal crisis risk; disease flare risk)	-	ROUTINE	ROUTINE
Monitor and report progressive difficulty climbing stairs, rising from chairs, reaching overhead, or lifting head from pillow (proximal weakness worsening)	-	ROUTINE	ROUTINE
Avoid sun exposure and use broad-spectrum SPF 50+ sunscreen daily for DM skin disease (UV light worsens DM rash)	-	ROUTINE	ROUTINE
Report any fever or signs of infection immediately to treating physician (immunosuppression increases infection risk)	-	ROUTINE	ROUTINE
Take medications as prescribed; bring complete medication list to ALL healthcare visits	-	ROUTINE	ROUTINE
Attend all scheduled follow-up appointments (CK monitoring and strength assessment are essential to guide treatment)	-	ROUTINE	ROUTINE
Do not drive if significant proximal weakness limits ability to safely operate vehicle pedals or steering	-	ROUTINE	ROUTINE
Use fall precautions including grab bars, non-slip mats, and assistive devices as recommended by PT/OT given proximal weakness	-	ROUTINE	ROUTINE
Rest before meals if dysphagia present; eat smaller, more frequent meals; sit upright for 30 min after eating	-	ROUTINE	ROUTINE
Report any new lump, unexplained weight loss, blood in stool/urine, or persistent pain (malignancy screening is important in myositis)	-	ROUTINE	ROUTINE

4C. Lifestyle & Prevention

Recommendation	ED	HOSP	OPD
Graded exercise program supervised by physical therapist -- low-impact aerobic exercise (walking, swimming, stationary bike) is safe and beneficial even during active disease; avoid eccentric/high-resistance exercise during active inflammation	-	ROUTINE	ROUTINE
Strict sun protection for all DM patients: broad-spectrum SPF 50+ daily, photoprotective clothing, wide-brimmed hat, avoid peak UV hours (10am-4pm)	-	ROUTINE	ROUTINE
Smoking cessation as smoking worsens ILD and impairs immune function	-	ROUTINE	ROUTINE
Balanced high-protein diet to support muscle recovery (1.2-1.5 g/kg/day protein); adequate calcium and vitamin D intake for bone health on steroids	-	ROUTINE	ROUTINE
Low-sodium diet to reduce fluid retention and blood pressure elevation on corticosteroids	-	ROUTINE	ROUTINE
Influenza vaccination (inactivated) annually; pneumococcal vaccination per schedule; avoid live vaccines during immunosuppression	-	ROUTINE	ROUTINE
Shingles vaccination (Shingrix -- non-live recombinant vaccine) if age >=50 or immunosuppressed	-	-	ROUTINE
Complete all vaccinations before starting immunosuppression when possible (ideally 4-6 weeks before rituximab)	-	ROUTINE	ROUTINE
Annual dermatologic exam for skin cancer screening given immunosuppression and DM skin disease	-	-	ROUTINE
Annual age-appropriate malignancy screening for 3-5 years after DM diagnosis (highest cancer risk in first 3 years)	-	-	ROUTINE
Energy conservation techniques: prioritize tasks, use adaptive equipment, plan rest periods throughout the day	-	ROUTINE	ROUTINE
Home safety evaluation to remove fall hazards given proximal weakness and fall risk	-	ROUTINE	ROUTINE
Alcohol limitation as alcohol interacts with methotrexate (hepatotoxicity) and immunosuppressants	-	ROUTINE	ROUTINE
Adequate sleep (7-9 hours) to promote immune health and muscle recovery	-	ROUTINE	ROUTINE

═══════════════════════════════════════════════════════════════ SECTION B: REFERENCE (Expand as Needed) ═══════════════════════════════════════════════════════════════

5. DIFFERENTIAL DIAGNOSIS

Alternative Diagnosis	Key Distinguishing Features	Tests to Differentiate
Inclusion body myositis (IBM)	Age >50; insidious onset; distal weakness (finger flexors, wrist flexors, quadriceps); asymmetric; refractory to immunotherapy; CK mildly elevated or normal	Muscle biopsy (rimmed vacuoles, eosinophilic inclusions, congophilic amyloid deposits); anti-cN1A antibody; EMG (mixed myopathic + neurogenic pattern)
Hypothyroid myopathy	Proximal weakness with fatigue; elevated CK (mild); hypothyroid symptoms (weight gain, cold intolerance, constipation); delayed relaxation of reflexes	TSH (elevated); free T4 (low); CK normalizes with thyroid replacement
Drug-induced myopathy (statins, colchicine, steroids)	Temporal correlation with drug initiation; statin myopathy most common; steroid myopathy causes proximal weakness without CK elevation	Drug history; CK may or may not be elevated (statin); improvement after drug discontinuation; EMG may be normal or myopathic; biopsy shows type 2 fiber atrophy (steroid myopathy)
Muscular dystrophy (limb-girdle, dystrophinopathy)	Earlier onset (variable); family history; progressive without remission; specific pattern of weakness; no rash	Genetic testing; CK elevated; muscle biopsy (dystrophic changes, absent/reduced protein on immunostaining); no inflammation or perifascicular atrophy
Motor neuron disease (ALS)	Fasciculations; upper motor neuron signs (hyperreflexia, Babinski); mixed UMN/LMN pattern; bulbar onset may mimic dysphagia; no rash; no CK elevation or mild only	EMG (widespread active denervation, fasciculations); normal muscle enzymes or mildly elevated CK; no myositis antibodies
Myasthenia gravis	Fatigable weakness (worse with repetitive use, improves with rest); ocular involvement (ptosis, diplopia); normal CK; intact reflexes	AChR/MuSK antibodies; RNS (decremental response); SFEMG (increased jitter); normal CK; ice pack test
Lambert-Eaton myasthenic syndrome (LEMS)	Proximal weakness with facilitation (improvement after brief exercise); autonomic dysfunction; often paraneoplastic (SCLC)	VGCC antibody; RNS (incremental response at high rate); CT chest for malignancy
Polymyalgia rheumatica (PMR)	Age >50; proximal pain/stiffness more than weakness; elevated ESR/CRP; rapid response to low-dose prednisone (15-20 mg); normal CK; normal strength on exam	ESR/CRP markedly elevated; CK normal; EMG normal; dramatic response to low-dose prednisone; PET/CT may show bursitis/synovitis
Endocrine myopathy (Cushing, Addison, hyperparathyroidism)	Associated endocrine symptoms; steroid myopathy presents with proximal weakness but normal CK; insidious onset	Cortisol, ACTH, calcium, PTH; CK normal in steroid myopathy; EMG may be normal; biopsy shows type 2 fiber atrophy
Metabolic myopathy (McArdle, Pompe, mitochondrial)	Exercise intolerance; second wind phenomenon (McArdle); ptosis and ophthalmoparesis (mitochondrial); infantile or late-onset forms (Pompe)	Acid alpha-glucosidase activity (Pompe); myophosphorylase activity (McArdle); lactate/pyruvate ratio; genetic testing; muscle biopsy (ragged red fibers, vacuoles)
Viral myositis (influenza, HIV, HTLV-1)	Acute onset with viral prodrome; self-limited in influenza; HIV/HTLV-1 chronic	Viral serology; self-limited course (influenza); HIV testing; biopsy if persistent
Sarcoidosis (muscular)	Granulomatous myopathy; systemic involvement (lungs, skin, eyes, lymph nodes); elevated ACE level	ACE level; chest CT (hilar lymphadenopathy); muscle biopsy (non-caseating granulomas); gallium scan or PET/CT
Parasitic myositis (trichinosis, toxoplasmosis)	Eosinophilia; travel/exposure history; periorbital edema (trichinosis); fever	Eosinophil count; serology; muscle biopsy (larvae/cysts)
Overlap myositis (SLE, scleroderma, Sjogren, MCTD)	Features of multiple autoimmune diseases; Raynaud phenomenon; sclerodactyly; sicca symptoms; malar rash	ANA, anti-dsDNA, anti-Scl-70, anti-U1 RNP, anti-SSA/SSB; specific overlap antibodies (anti-PM-Scl, anti-Ku)

6. MONITORING PARAMETERS

Parameter	ED	HOSP	OPD	ICU	Frequency	Target/Threshold	Action if Abnormal
Creatine kinase (CK)	STAT	STAT	ROUTINE	STAT	q24-48h inpatient during acute phase; q2-4 weeks outpatient during treatment; q3 months when stable	Declining toward normal with treatment; CK normalization expected in 6-12 weeks	If CK rising or not declining: reassess immunotherapy intensity; check compliance; consider refractory disease or alternative diagnosis
Muscle strength (MMT)	STAT	STAT	ROUTINE	STAT	Each visit; standardized manual muscle testing of proximal groups (deltoid, hip flexors, neck flexors)	MRC grade 4+/5 or better in proximal muscles	If worsening: increase immunotherapy; reassess diagnosis; consider biopsy if not done
FVC and DLCO (PFTs)	-	ROUTINE	ROUTINE	-	Baseline then q3-6 months; q1-2 months if ILD present or anti-MDA5/anti-Jo-1 positive	FVC >80% predicted; DLCO >80% predicted; stable or improving	If declining >10% FVC or >15% DLCO: escalate ILD treatment; pulmonology referral; repeat HRCT
HRCT chest	-	ROUTINE	ROUTINE	-	Baseline; repeat q6-12 months if ILD present; sooner if symptoms worsen	Stable or improving ILD findings	If progressive: escalate immunotherapy (cyclophosphamide, rituximab, JAK inhibitor); consider lung transplant referral if refractory
Blood glucose	STAT	STAT	ROUTINE	STAT	q6h during pulse steroids; daily during high-dose oral; HbA1c q3 months on chronic steroids	Glucose <180 inpatient; HbA1c <7%	Insulin sliding scale; endocrine consult if persistent hyperglycemia; attempt steroid taper
CBC with differential	-	ROUTINE	ROUTINE	-	q2-4 weeks during immunosuppressant titration; then q4-8 weeks when stable	WBC >3000; ANC >1500; lymphocytes >500; platelets >100K	Hold/reduce immunosuppressant if cytopenic; G-CSF if severe neutropenia; infection evaluation if febrile
LFTs (AST, ALT, ALP, bilirubin)	-	ROUTINE	ROUTINE	-	q2-4 weeks during methotrexate/azathioprine titration; then q8-12 weeks	AST/ALT <3x ULN (distinguish muscle vs hepatic source by correlating with CK)	If hepatic transaminases rising (disproportionate to CK): hold offending agent; hepatology referral; consider alternative steroid-sparing agent
Renal function (BUN, Cr)	STAT	STAT	ROUTINE	STAT	q24h during rhabdomyolysis; q1-3 months on tacrolimus; q3 months otherwise	Normal eGFR; stable creatinine	If declining: aggressive hydration during rhabdomyolysis; dose-adjust nephrotoxic agents; nephrology referral
TPMT genotype/activity (before azathioprine)	-	ROUTINE	ROUTINE	-	Once before starting azathioprine	Normal activity (heterozygous: reduce dose 50%; homozygous deficient: contraindicated)	Adjust or avoid azathioprine based on TPMT status
Tacrolimus trough level	-	ROUTINE	ROUTINE	-	q1-2 weeks during titration; then q1-3 months	5-10 ng/mL	Dose adjustment based on level and clinical response
CD19/CD20 B-cell counts (if on rituximab)	-	ROUTINE	ROUTINE	-	q3-6 months	Depleted B-cells (therapeutic)	Redose rituximab when B-cells recover and symptoms worsen
Immunoglobulin levels (IgG, IgA, IgM)	-	ROUTINE	ROUTINE	-	q6 months if on rituximab or chronic immunosuppression	IgG >400 mg/dL	IVIG replacement if symptomatic hypogammaglobulinemia with recurrent infections
Swallowing function	URGENT	STAT	ROUTINE	STAT	Daily if dysphagia present; each clinic visit	Safe oral intake	NPO if aspiration risk; SLP reevaluation; may need NG tube or PEG
DEXA scan (bone density)	-	-	ROUTINE	-	Baseline if starting chronic steroids; repeat q2 years	T-score >-1.0	Bisphosphonate; calcium/vitamin D; endocrine referral
Ophthalmologic exam (if on HCQ)	-	-	ROUTINE	-	Baseline; annual after 5 years (or 1 year if high risk)	Normal retina; no HCQ toxicity	Discontinue HCQ if retinal toxicity detected
Malignancy screening (DM patients)	-	ROUTINE	ROUTINE	-	At diagnosis; annually for 3-5 years after DM diagnosis; comprehensive if anti-TIF1-gamma positive	No malignancy	Oncology referral if malignancy identified
Cardiac monitoring (troponin, ECG, echo)	URGENT	ROUTINE	ROUTINE	URGENT	Baseline; repeat if symptoms; annually if anti-SRP positive	Normal cardiac function	Cardiology referral; cardiac MRI if troponin elevated
Urine output and urine color	STAT	STAT	-	STAT	Hourly during rhabdomyolysis; daily inpatient otherwise	>0.5 mL/kg/h; clear urine	Aggressive IV hydration; consider bicarbonate drip; nephrology if oliguric

7. DISPOSITION CRITERIA

Disposition	Criteria
Discharge home	Mild myositis with preserved functional ability (able to rise from chair, climb stairs, lift arms overhead); stable CK and trending down; adequate oral intake and safe swallow; oral medications tolerated; no ILD or stable ILD; reliable outpatient follow-up within 1-2 weeks; understands return precautions
Admit to floor	Moderate-severe proximal weakness (unable to rise from chair or climb stairs without assistance); CK >5000 or rising; new diagnosis requiring expedited workup including muscle biopsy; dysphagia requiring diet modification; ILD requiring monitoring; IVIG infusion; steroid initiation with monitoring needs
Admit to ICU	Rhabdomyolysis with CK >10,000 and myoglobinuria (renal failure risk); respiratory failure from ILD (especially anti-MDA5 rapidly progressive ILD); severe dysphagia with aspiration pneumonia; cardiac involvement (myocarditis, arrhythmia); hemodynamic instability during PLEX
Transfer to higher level of care	Need for PLEX not available on-site; need for muscle biopsy with neuromuscular pathology expertise; neuromuscular specialist not available; rapidly progressive ILD requiring advanced respiratory support; consideration for lung transplant evaluation
Inpatient rehabilitation	Significant proximal weakness limiting ADLs (unable to walk independently); able to participate in 3h/day therapy; medically stable; oral medications established; no active rhabdomyolysis
Skilled nursing facility	Unable to tolerate intensive rehabilitation; requires ongoing nursing care; severe deconditioning; chronic high-level care needs

8. EVIDENCE & REFERENCES

Recommendation	Evidence Level	Source
IVIG for dermatomyositis (ProDERM trial)	Class I, Level A	Aggarwal R et al. NEJM 2022
Myositis-specific antibody classification and clinical significance	Class II, Level B	Betteridge Z et al. Nat Rev Rheumatol 2020
Anti-TIF1-gamma association with malignancy in DM	Class II, Level B	Trallero-Araguas E et al. Rheumatology 2012; Oldroyd A et al. Rheumatology 2019
Anti-MDA5 and rapidly progressive ILD	Class II, Level B	Sato S et al. Arthritis Rheum 2009; Moghadam-Kia S et al. Chest 2016
Anti-SRP and immune-mediated necrotizing myopathy	Class II, Level B	Hengstman GJ et al. Ann Neurol 2006; Allenbach Y et al. Neurology 2014
Anti-HMGCR necrotizing myopathy	Class II, Level B	Mammen AL et al. N Engl J Med 2011
High-dose corticosteroids as first-line treatment	Class II, Level B	Expert consensus; Oddis CV, Aggarwal R. Nat Rev Rheumatol 2018
Methotrexate as steroid-sparing agent	Class II, Level B	Bunch TW et al. Medicine 1980
Azathioprine as steroid-sparing agent	Class II, Level B	Bunch TW et al. Medicine 1980
Mycophenolate for inflammatory myopathy	Class II, Level B	Rowin J et al. Neurology 2006; Pisoni CN et al. Rheumatology 2007
Rituximab for refractory inflammatory myopathy (RIM trial)	Class I, Level B	Oddis CV et al. Arthritis Rheum 2013
Cyclophosphamide for ILD in anti-synthetase syndrome	Class II, Level C	Fischer A et al. J Rheumatol 2006
Triple therapy (steroids + tacrolimus + cyclophosphamide) for anti-MDA5 ILD	Class II, Level C	Tsuji H et al. Rheumatology 2020
JAK inhibitors (tofacitinib) for refractory DM	Class III (case series)	Chen Z et al. Clin Rheumatol 2021; Paik JJ et al. Brain 2021
Hydroxychloroquine for DM skin disease	Class II, Level C	Ang GC, Werth VP. Curr Rheumatol Rep 2005
ENMC classification of inflammatory myopathies	Expert consensus	Hoogendijk JE et al. Neuromuscul Disord 2004
ACR/EULAR classification criteria for idiopathic inflammatory myopathies	Class I	Lundberg IE et al. Ann Rheum Dis 2017
Muscle biopsy findings in DM vs PM vs IMNM	Class II	Dalakas MC. NEJM 2015
Malignancy screening in dermatomyositis	Class II, Level B	Hill CL et al. Lancet 2001; Olazagasti JM et al. Arthritis Care Res 2015
MRI for guiding muscle biopsy site selection	Class II, Level B	Tomasova Studynkova J et al. Rheumatology 2007
Exercise safety and benefit in inflammatory myopathy	Class I, Level B	Alemo Munters L et al. Arthritis Res Ther 2013
Anti-synthetase syndrome clinical spectrum	Class II	Connors GR et al. Semin Respir Crit Care Med 2010
DVT prophylaxis in immobilized patients	Class I, Level C	Standard of care for immobilized patients
PCP prophylaxis during immunosuppression	Class II, Level C	Expert consensus; standard infectious disease practice
Rhabdomyolysis management with aggressive IV hydration	Class II, Level B	Bosch X et al. NEJM 2009
Dysphagia management in inflammatory myopathy	Class II, Level C	Oh TH et al. Semin Arthritis Rheum 2007

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CHANGE LOG

v1.1 (January 30, 2026) - Standardized structured dosing format across all treatment sections (3A, 3B, 3C, 3D) to use [dose] :: [route] :: [frequency] :: [full_instructions] pattern - Eliminated all cross-references: replaced "Same as initial IVIG" in Second course IVIG row with full contraindications and monitoring content - Eliminated all cross-references: replaced "See individual agents above" in anti-MDA5 triple therapy row with complete contraindications and monitoring details - Fixed Prednisone (chronic taper) row in 3D: added missing Pre-Treatment Requirements column - Fixed SCIg row in 3D: added missing Pre-Treatment Requirements column - Fixed Plasmapheresis route column from "-" to "Extracorporeal" - Added structured dosing format to sunscreen row (was missing :: delimiters) - Eliminated cross-references in Section 2B/2C imaging: replaced "Same as thigh MRI" and "Same as standard MRI" with full contraindication lists - Updated version to 1.1

v1.0 (January 30, 2026) - Initial template creation - Section 1: 50+ laboratory tests across 3 tiers - 1A: 17 core labs (CK, CMP, aldolase, LDH, AST/ALT, inflammatory markers) - 1B: 30 extended labs (comprehensive myositis-specific antibody panel: anti-Jo-1, anti-Mi-2, anti-MDA5, anti-NXP2, anti-TIF1-gamma, anti-SRP, anti-HMGCR, anti-PL-7, anti-PL-12, anti-EJ, anti-OJ, anti-SAE; CTD overlap antibodies; troponin; ferritin; infection screen) - 1C: 11 rare/specialized (anti-cN1A, IL-18, KL-6, genetic testing for hereditary myopathy mimics) - Section 2: Imaging and studies across 3 tiers - 2A: MRI thighs, CXR, HRCT chest (ILD screening), ECG, PFTs with DLCO, echocardiogram - 2B: EMG/NCS, CT chest/abdomen/pelvis (malignancy), PET/CT, cardiac MRI, barium swallow - 2C: Muscle biopsy, skin biopsy, mammography, colonoscopy, nailfold capillaroscopy, RHC - Section 3: Treatment across 4 subsections - 3A: Acute/emergent (9 items: IV methylprednisolone pulse, prednisone, IVIG, PLEX, GI prophylaxis, DVT prophylaxis, rhabdomyolysis management) - 3B: Symptomatic (12 items: analgesics, HCQ, skin treatments, bone protection, PCP prophylaxis, gabapentin) - 3C: Second-line/refractory (7 items: rituximab, JAK inhibitors, tacrolimus rescue, cyclophosphamide, anti-MDA5 triple therapy) - 3D: Disease-modifying chronic therapies (7 items: methotrexate, azathioprine, mycophenolate, tacrolimus, chronic prednisone taper, IVIG maintenance, SCIg) - Section 4: Recommendations across 3 subsections - 4A: 17 referrals (neuromuscular, rheumatology, pulmonology, dermatology, oncology, SLP, PT, OT, cardiology, GI, gynecology, social work, infusion center, pain management, psychiatry, nutrition, palliative care) - 4B: 15 patient instructions - 4C: 14 lifestyle/prevention recommendations - Section 5: 14 differential diagnoses (IBM, hypothyroid, drug-induced, LGMD, ALS, MG, LEMS, PMR, endocrine, metabolic, viral, sarcoid, parasitic, overlap) - Section 6: 18 monitoring parameters with venue-specific coverage - Section 7: 6 disposition criteria levels - Section 8: 26 evidence citations with PubMed links

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APPENDIX A: MYOSITIS-SPECIFIC ANTIBODY QUICK REFERENCE

Antibody	Disease Subtype	Key Clinical Features	Malignancy Risk	ILD Risk	Prognosis
Anti-Jo-1	Anti-synthetase syndrome	Myositis + ILD + mechanic's hands + arthritis + Raynaud + fever	Low-moderate	HIGH (50-70%)	Moderate; ILD determines outcome
Anti-PL-7	Anti-synthetase syndrome	ILD-predominant; less severe myositis	Low	HIGH	Moderate
Anti-PL-12	Anti-synthetase syndrome	ILD-predominant; minimal myositis	Low	HIGH	Moderate
Anti-EJ	Anti-synthetase syndrome	Myositis + ILD	Low	HIGH	Moderate
Anti-OJ	Anti-synthetase syndrome	ILD + myositis	Low	HIGH	Moderate
Anti-Mi-2	Classic DM	Heliotrope rash, Gottron papules, V-sign; good steroid response	Low	Low	Good
Anti-MDA5 (CADM-140)	Amyopathic DM	Rapidly progressive ILD (HIGH MORTALITY); skin ulcers; palmar papules; minimal myositis; high ferritin	Low	VERY HIGH (fatal if untreated)	Poor without aggressive treatment
Anti-TIF1-gamma (p155/140)	DM with malignancy	Classic DM rash; up to 60% malignancy risk in adults >40	VERY HIGH	Low	Depends on malignancy; DM may remit with cancer treatment
Anti-NXP2 (MJ)	DM with calcinosis	Calcinosis (especially juvenile); peripheral edema; severe weakness	Moderate (adults)	Low	Variable
Anti-SAE	DM	Initial skin-predominant then develops myopathy; dysphagia common	Low-moderate	Low	Moderate
Anti-SRP	IMNM	Severe proximal weakness; very high CK; cardiac involvement; poor steroid response; requires aggressive immunotherapy	Low	Low	Poor without combination therapy
Anti-HMGCR	IMNM	Often statin-associated (but can occur without statins); very high CK; severe proximal weakness; requires aggressive immunotherapy	Low	Low	Moderate-poor without combination therapy

APPENDIX B: ACR/EULAR CLASSIFICATION CRITERIA (2017)

Probability-based classification for idiopathic inflammatory myopathies (IIM):

Variable	Without Biopsy	With Biopsy
Age at onset >=18 and <40	1.3	1.5
Age at onset >=40	2.1	2.2
Male sex	0.0	0.0
Female sex	0.0	0.0
Muscle weakness (upper extremities proximal)	0.7	0.7
Muscle weakness (lower extremities proximal)	0.5	0.5
Neck flexor weakness	1.9	1.9
Objective symmetric weakness (proximal upper > distal)	0.6	0.6
Dysphagia	0.7	0.7
Heliotrope rash	3.1	3.2
Gottron papules	2.1	2.7
Gottron sign	3.3	3.5
Elevated CK or LDH or AST or ALT	1.3	1.4
Anti-Jo-1 positive	3.9	3.8
Muscle biopsy: endomysial inflammation	-	1.7
Muscle biopsy: perimysial/perivascular inflammation	-	1.2
Muscle biopsy: perifascicular atrophy	-	1.9
Muscle biopsy: rimmed vacuoles	-	3.1

Score Interpretation: - Definite IIM: aggregate score >=7.5 (without biopsy) or >=8.7 (with biopsy) - Probable IIM: aggregate score >=5.5 (without biopsy) or >=6.7 (with biopsy) - Possible IIM: aggregate score >=5.3 (without biopsy) or >=6.5 (with biopsy)

Subclassification: Once classified as IIM, further classified into DM, PM, IBM, amyopathic DM, or juvenile DM based on specific criteria including rash, biopsy findings, and antibody status.

APPENDIX C: MALIGNANCY SCREENING PROTOCOL FOR DERMATOMYOSITIS

Risk stratification:

Risk Factor	Screening Level
Anti-TIF1-gamma positive + age >40	Comprehensive (highest risk)
Any adult-onset DM, age >40	Enhanced
DM age 18-40	Standard age-appropriate
PM or IMNM without DM features	Standard age-appropriate
Juvenile DM	Standard pediatric

Comprehensive malignancy screening (high-risk DM):

Screening Test	Timing	Repeat
CT chest/abdomen/pelvis with contrast	At diagnosis	Annually x 3 years
PET/CT (FDG)	At diagnosis if CT negative	As clinically indicated
Mammography (female)	At diagnosis	Annually x 3 years
Pelvic ultrasound (female)	At diagnosis	Annually x 3 years
CA-125 (female)	At diagnosis	Annually x 3 years
PSA (male)	At diagnosis	Annually x 3 years
Colonoscopy	At diagnosis (if age >45 or symptoms)	Per gastroenterology
Upper endoscopy	If symptoms or nasopharyngeal carcinoma risk (Asian descent)	As indicated
Urinalysis with cytology	At diagnosis	Annually x 3 years
Complete blood count with differential	At diagnosis	q3-6 months
Age-appropriate cancer screening	Per guidelines	Per guidelines

Key points: - Highest cancer risk is within first 3 years of DM diagnosis - Most common malignancies: ovarian, lung, breast, GI, pancreatic, nasopharyngeal (geographic variation) - DM may be a paraneoplastic syndrome; treating underlying malignancy may improve myositis - Anti-TIF1-gamma negative predictive value is high; absence significantly reduces cancer risk - Annual screening recommended for minimum 3-5 years after DM diagnosis