Myotonic Dystrophy¶

VERSION: 1.1 CREATED: January 30, 2026 REVISED: January 31, 2026 STATUS: Draft - Pending Review

DIAGNOSIS: Myotonic Dystrophy (DM1 and DM2)

ICD-10: G71.11 (Myotonic muscular dystrophy, type 1 -- DM1/Steinert disease), G71.12 (Myotonic muscular dystrophy, type 2 -- DM2/PROMM), G71.19 (Other specified myotonic disorders)

SYNONYMS: Myotonic dystrophy type 1, DM1, Steinert disease, dystrophia myotonica type 1, myotonic dystrophy type 2, DM2, proximal myotonic myopathy, PROMM, myotonic muscular dystrophy, Curschmann-Steinert disease, Curschmann-Batten-Steinert syndrome

SCOPE: Evaluation and management of myotonic dystrophy type 1 (DM1) and type 2 (DM2) across care settings. Includes diagnostic workup, genetic testing, multisystem assessment (cardiac, respiratory, endocrine, GI, ophthalmologic), symptomatic management of myotonia, and chronic disease monitoring. Covers anesthesia precautions and genetic counseling. Excludes congenital myotonic dystrophy (CDM -- pediatric onset), non-dystrophic myotonias (myotonia congenita, paramyotonia congenita -- see separate plans), and other muscular dystrophies (FSHD, LGMD -- see separate plans).

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	Rationale	Target Finding	ED	HOSP	OPD	ICU
Creatine kinase (CK) (CPT 82550)	Muscle enzyme; typically mildly elevated in DM1 (1-3x ULN) and normal to mildly elevated in DM2; aids in distinguishing from inflammatory myopathies	Normal (30-200 U/L); expect mild elevation (200-600 U/L in DM1; often normal in DM2)	STAT	STAT	ROUTINE	STAT
CMP (BMP + LFTs) (CPT 80053)	Renal function baseline; hepatic function; AST/ALT may be mildly elevated from muscle source; glucose assessment given diabetes risk	Normal; mildly elevated AST/ALT may reflect muscle origin	STAT	STAT	ROUTINE	STAT
CBC with differential (CPT 85025)	Baseline blood counts; infection screen if presenting acutely; IgG deficiency and immunologic abnormalities occur in DM1	Normal; mild leukopenia possible	STAT	STAT	ROUTINE	STAT
Fasting glucose (CPT 82947)	Insulin resistance and diabetes mellitus are common in DM1 (25-75%); screening essential for multisystem management	Normal (<100 mg/dL); impaired fasting glucose or diabetes common	STAT	STAT	ROUTINE	STAT
HbA1c (CPT 83036)	Diabetes screening and monitoring; insulin resistance frequent in DM1; less common in DM2	<5.7% normal; 5.7-6.4% prediabetes; >=6.5% diabetes	URGENT	ROUTINE	ROUTINE	-
TSH (CPT 84443)	Thyroid dysfunction (hypothyroidism) occurs in myotonic dystrophy; contributes to fatigue and weakness	Normal (0.4-4.0 mIU/L)	URGENT	ROUTINE	ROUTINE	-
Free T4 (CPT 84439)	Complement TSH if abnormal; hypothyroidism common in DM1	Normal (0.8-1.8 ng/dL)	URGENT	ROUTINE	ROUTINE	-
Liver function tests (ALT, AST, ALP, bilirubin, albumin) (CPT 80076)	Hepatic involvement in DM1; fatty liver and elevated GGT common; baseline before hepatotoxic medications	Normal; mildly elevated GGT and ALT common in DM1	STAT	STAT	ROUTINE	STAT
Magnesium (CPT 83735)	Hypomagnesemia can exacerbate cardiac conduction abnormalities and myotonia	Normal (1.7-2.2 mg/dL)	STAT	STAT	ROUTINE	STAT
Calcium (CPT 82310)	Hypocalcemia/hypercalcemia can affect myotonia and cardiac conduction	Normal (8.5-10.5 mg/dL)	STAT	STAT	ROUTINE	STAT
Lipid panel (CPT 80061)	Dyslipidemia screening; metabolic syndrome common in DM1	Total cholesterol <200; LDL <130; triglycerides <150	-	ROUTINE	ROUTINE	-
Urinalysis (CPT 81001)	Baseline renal assessment; screen for myoglobinuria if acute presentation	Normal; no myoglobin	STAT	ROUTINE	ROUTINE	STAT

1B. Extended Workup (Second-line)¶

Test	Rationale	Target Finding	ED	HOSP	OPD	ICU
Genetic testing: DMPK gene CTG repeat expansion (DM1) (CPT 81401)	Definitive diagnosis of DM1; CTG trinucleotide repeat expansion on chromosome 19q13.3; normal <37 repeats; DM1 = 50 to >2000 repeats; repeat length correlates with severity and age of onset	Normal <37 CTG repeats; mild DM1 50-150; classic DM1 100-1000; congenital DM1 >1000	-	URGENT	ROUTINE	-
Genetic testing: CNBP (ZNF9) gene CCTG repeat expansion (DM2) (CPT 81401)	Definitive diagnosis of DM2; CCTG tetranucleotide repeat expansion on chromosome 3q21.3; normal <26 repeats; DM2 = 75 to >11,000 repeats; no clear genotype-phenotype correlation	Normal <26 CCTG repeats; DM2 typically 75 to >11,000 repeats	-	URGENT	ROUTINE	-
Testosterone (total and free) (CPT 84402, 84403)	Hypogonadism common in DM1 males (60-80%); testicular atrophy; contributes to fatigue, reduced muscle mass, erectile dysfunction	Normal male: total 300-1000 ng/dL; expect low or low-normal in DM1	-	ROUTINE	ROUTINE	-
FSH, LH (CPT 83001, 83002)	Evaluate hypogonadal axis; primary vs secondary hypogonadism in DM1	Normal or elevated FSH/LH (primary hypogonadism pattern in DM1)	-	ROUTINE	ROUTINE	-
Estradiol (CPT 82670)	Evaluate gonadal function in females with DM1; menstrual irregularities and early menopause	Normal for age and menstrual phase	-	ROUTINE	ROUTINE	-
Fasting insulin (CPT 83525)	Insulin resistance assessment; hyperinsulinemia precedes overt diabetes in DM1	Normal (<25 mIU/L fasting); elevated insulin with normal glucose suggests insulin resistance	-	ROUTINE	ROUTINE	-
Immunoglobulin levels (IgG, IgA, IgM) (CPT 82784, 82787)	Hypogammaglobulinemia (especially IgG) occurs in DM1; increased infection susceptibility	Normal IgG (700-1600 mg/dL); low IgG may explain recurrent infections	-	ROUTINE	ROUTINE	-
GGT (CPT 82977)	Elevated in DM1 even without alcohol use; marker of hepatic involvement; distinguish from alcohol-related elevation	Normal (<60 U/L); expect mild-moderate elevation in DM1	-	ROUTINE	ROUTINE	-
Vitamin D (25-OH) (CPT 82306)	Deficiency common; worsens weakness and fall risk; important for bone health in patients with limited mobility	>30 ng/mL	-	ROUTINE	ROUTINE	-
Iron studies (ferritin, TIBC, serum iron) (CPT 82728, 83550, 83540)	Fatigue evaluation; iron deficiency common cause of fatigue superimposed on DM-related fatigue	Normal ferritin (30-300 ng/mL); normal iron and TIBC	-	ROUTINE	ROUTINE	-
PT/INR (CPT 85610), aPTT (CPT 85730)	Coagulation baseline if muscle biopsy needed or pre-procedural	Normal	STAT	ROUTINE	-	-

1C. Rare/Specialized (Refractory or Atypical)¶

Test	Rationale	Target Finding	ED	HOSP	OPD	ICU
Myotonia-specific genetic panel (expanded)	If DM1 and DM2 testing negative; includes CLCN1 (myotonia congenita), SCN4A (paramyotonia congenita, sodium channel myotonia), KCNJ2 (Andersen-Tawil)	Negative for DM1/DM2 mutations; may identify non-dystrophic myotonia	-	-	EXT	-
Myositis-specific antibody panel (CPT 86235)	If inflammatory myopathy in differential; elevated CK with proximal weakness and unclear genetic testing	Negative; positive suggests alternative diagnosis	-	ROUTINE	EXT	-
Acid alpha-glucosidase activity (dried blood spot) (CPT 82657)	Late-onset Pompe disease in differential if proximal weakness and respiratory insufficiency without myotonia	Normal enzyme activity; reduced suggests Pompe disease	-	ROUTINE	EXT	-
BNP or NT-proBNP (CPT 83880)	Cardiac involvement assessment; heart failure screening in symptomatic DM1 patients	Normal BNP (<100 pg/mL); elevated suggests cardiac dysfunction	STAT	ROUTINE	ROUTINE	STAT
Troponin (CPT 84484)	Acute cardiac injury evaluation if presenting with chest pain or arrhythmia	Normal; elevated suggests myocardial injury	STAT	STAT	-	STAT
Sleep study referral labs: ABG or SpO2 (CPT 82803)	Respiratory assessment if hypoventilation or excessive daytime somnolence suspected	Normal PaCO2 (35-45 mmHg); SpO2 >95%; elevated PaCO2 suggests hypoventilation	STAT	ROUTINE	ROUTINE	STAT

2. DIAGNOSTIC IMAGING & STUDIES¶

2A. Essential/First-line¶

Study	Timing	Target Finding	Contraindications	ED	HOSP	OPD	ICU
ECG (12-lead) (CPT 93000)	At presentation and annually; critical for cardiac conduction abnormality screening (leading cause of sudden death in DM1)	Normal sinus rhythm; look for first-degree AV block (PR >200ms), bundle branch block, QTc prolongation, atrial flutter/fibrillation; any conduction abnormality requires cardiology referral	None	STAT	STAT	ROUTINE	STAT
EMG/NCS (CPT 95886, 95907-95913)	During initial workup; essential for diagnosis	Myotonic discharges (waxing-and-waning "dive bomber" sound); myopathic MUAPs (short duration, low amplitude, early recruitment); fibrillations and positive sharp waves; NCS usually normal	None significant; avoid anticoagulated limbs for needle EMG	-	URGENT	ROUTINE	-
Chest X-ray (PA and lateral) (CPT 71046)	At presentation; baseline; respiratory assessment	Baseline lung fields; elevated hemidiaphragm suggests diaphragmatic weakness; aspiration pneumonia	None significant	URGENT	ROUTINE	ROUTINE	STAT
Slit-lamp ophthalmologic exam	Within first 3 months of diagnosis; annual thereafter	Posterior subcapsular cataracts (iridescent "Christmas tree" cataracts pathognomonic for DM1); found in >90% of DM1 and common in DM2	None	-	ROUTINE	ROUTINE	-

2B. Extended¶

Study	Timing	Target Finding	Contraindications	ED	HOSP	OPD	ICU
24-hour Holter monitor (CPT 93224)	At diagnosis and annually; more frequently if symptomatic or conduction abnormality on ECG	Normal rhythm; detect intermittent AV block, atrial fibrillation/flutter, ventricular tachycardia, prolonged pauses (>2.5 sec); DM1 patients at risk for sudden cardiac death	None significant	-	ROUTINE	ROUTINE	-
Echocardiogram (CPT 93306)	At diagnosis; repeat if symptoms or ECG changes	Normal LV function (EF >55%); assess for LV systolic dysfunction, diastolic dysfunction, mitral valve prolapse (common in DM1); wall motion abnormalities	None significant	URGENT	ROUTINE	ROUTINE	URGENT
Pulmonary function tests (PFTs) with DLCO (CPT 94010, 94729)	At diagnosis and annually; essential for respiratory monitoring	FVC >80% predicted; restrictive pattern (reduced FVC, normal FEV1/FVC ratio); MIP/MEP reduced (respiratory muscle weakness); DLCO usually normal	Unable to cooperate; active pneumothorax	-	ROUTINE	ROUTINE	-
Maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP) (CPT 94750)	At diagnosis and annually; sensitive for respiratory muscle weakness	MIP >60 cm H2O; MEP >40 cm H2O; reduced values indicate diaphragmatic and respiratory muscle weakness requiring intervention	Unable to cooperate	-	ROUTINE	ROUTINE	-
Polysomnography (sleep study) (CPT 95810)	If excessive daytime somnolence (very common in DM1), snoring, or FVC <70% predicted	No obstructive or central sleep apnea; DM1 patients frequently have OSA, central apnea, and/or sleep-disordered breathing; AHI <5 normal	None significant	-	ROUTINE	ROUTINE	-
MRI brain (with and without contrast) (CPT 70553)	If cognitive decline, behavioral changes, or excessive somnolence beyond expected for DM1	White matter hyperintensities (common in DM1); temporal lobe atrophy; cerebral atrophy; assess for extent of CNS involvement	Pacemaker (relative), metallic implants, severe claustrophobia, GFR <30 (gadolinium)	-	ROUTINE	EXT	-
Modified barium swallow study (MBSS) (CPT 74230)	If dysphagia symptoms present; oropharyngeal weakness common in DM1	Normal swallow mechanics; DM1 may show delayed pharyngeal transit, vallecular residue, aspiration or penetration	None significant	-	ROUTINE	ROUTINE	-
MRI thighs (bilateral, with and without contrast) (CPT 73721)	For disease monitoring or if diagnosis uncertain; assess muscle involvement pattern	DM1: preferential fatty infiltration of medial gastrocnemius, soleus, tibialis anterior (distal > proximal); DM2: preferential involvement of hip flexors, hip extensors, quadriceps (proximal > distal)	Pacemaker, metallic implants, severe claustrophobia, GFR <30 (gadolinium)	-	EXT	EXT	-

2C. Rare/Specialized¶

Study	Timing	Target Finding	Contraindications	ED	HOSP	OPD	ICU
Cardiac MRI (CPT 75561)	If echocardiogram abnormal or high clinical suspicion for myocardial fibrosis; risk stratification for sudden cardiac death	Normal myocardium; late gadolinium enhancement indicates fibrosis/scarring (predictor of arrhythmia risk); assess LV function	Pacemaker (relative -- MRI-conditional devices acceptable), metallic implants, GFR <30 (gadolinium)	-	EXT	EXT	-
Electrophysiology study (EPS) (CPT 93620)	If syncope, near-syncope, or significant conduction abnormalities; risk stratification for sudden cardiac death	Normal conduction intervals; prolonged HV interval (>70ms) predicts high-degree AV block risk and may warrant pacemaker/ICD	Active infection; coagulopathy	-	EXT	EXT	-
Muscle biopsy (CPT 20200)	Only if genetic testing inconclusive and diagnosis uncertain; rarely needed given availability of genetic testing	DM1: increased central nuclei, type 1 fiber atrophy, ring fibers, sarcoplasmic masses, pyknotic nuclear clumps; DM2: type 2 fiber atrophy (distinguishing feature), nuclear clumps	Coagulopathy; anticoagulation (hold); infection at site	-	EXT	EXT	-
Neuropsychological testing (CPT 96132)	If cognitive concerns or behavioral changes; DM1 frequently involves CNS (executive dysfunction, apathy, visuospatial deficits)	Normal for age; DM1 patients often show executive dysfunction, reduced processing speed, apathy, attention deficits, reduced motivation; DM2 milder cognitive involvement	Unable to cooperate	-	-	EXT	-
Gastric emptying study (CPT 78264)	If gastroparesis symptoms (nausea, bloating, early satiety, vomiting); GI dysmotility common in DM1	Normal gastric emptying (>90% at 4 hours); delayed emptying indicates gastroparesis	None significant	-	EXT	ROUTINE	-

3. TREATMENT¶

3A. Acute/Emergent¶

Treatment	Route	Indication	Dosing	Contraindications	Monitoring	ED	HOSP	OPD	ICU
IV fluids (normal saline)	IV	Dehydration; fall-related injury; rhabdomyolysis (rare); aspiration pneumonia hydration support	125 mL/h :: IV :: continuous :: 125-250 mL/h NS for hydration; increase rate if CK significantly elevated; monitor for heart failure given cardiac involvement in DM	Heart failure; volume overload (common cardiac comorbidity in DM1)	Urine output; electrolytes; fluid balance; cardiac status	STAT	STAT	-	STAT
Acetaminophen	PO	Pain management for fall-related injuries; myalgia; headache	650 mg :: PO :: q6h PRN :: 650-1000 mg PO q6h PRN pain; max 4 g/day (2 g/day if hepatic impairment -- liver involvement common in DM1)	Severe liver disease; hepatic impairment (reduce dose -- GGT/ALT often elevated in DM1)	LFTs if prolonged use	STAT	STAT	ROUTINE	STAT
Aspiration pneumonia treatment: Ampicillin-sulbactam	IV	Aspiration pneumonia from DM1-related dysphagia and oropharyngeal weakness	3 g :: IV :: q6h :: 3 g (ampicillin 2 g / sulbactam 1 g) IV q6h; duration 5-7 days; transition to oral amoxicillin-clavulanate when clinically improving	Penicillin allergy; severe hepatic impairment	Temperature; WBC; chest X-ray improvement; renal function	STAT	STAT	-	STAT
Aspiration pneumonia treatment: Clindamycin (penicillin allergy alternative)	IV	Aspiration pneumonia in penicillin-allergic patients with DM-related dysphagia	600 mg :: IV :: q8h :: 600-900 mg IV q8h; duration 5-7 days; transition to oral clindamycin 300-450 mg q6h when improving	Clindamycin hypersensitivity; C. difficile history (relative -- GI dysmotility in DM increases risk)	C. difficile monitoring; LFTs; diarrhea (GI dysmotility already present)	STAT	STAT	-	STAT
DVT prophylaxis: Enoxaparin	SC	VTE prevention in immobilized patients admitted with fall-related injuries or acute deconditioning	40 mg :: SC :: daily :: 40 mg SC daily; start on admission if immobile; hold if active bleeding	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 (CrCl <30)	5000 units :: SC :: q8-12h :: 5000 units SC q8-12h	Active bleeding; HIT history	Platelets q3 days	-	ROUTINE	-	ROUTINE

3B. Symptomatic Treatments¶

Treatment	Route	Indication	Dosing	Contraindications	Monitoring	ED	HOSP	OPD	ICU
Mexiletine	PO	First-line treatment for symptomatic myotonia (grip myotonia, jaw myotonia, difficulty releasing objects); sodium channel blocker that reduces myotonic stiffness	150 mg :: PO :: BID :: Start 150 mg PO BID; increase to 150 mg TID after 1-2 weeks; may increase to 200 mg TID; max 900 mg/day; take with food to reduce GI side effects	Second- or third-degree AV block (without pacemaker); cardiogenic shock; hepatic impairment; QTc prolongation; CRITICAL: obtain ECG before starting -- cardiac conduction disease common in DM1	ECG at baseline and 1-2 weeks after dose changes; LFTs q6-12 months; CBC; heart rate; GI tolerance; cardiac symptoms	-	ROUTINE	ROUTINE	-
Modafinil	PO	Excessive daytime somnolence (EDS) and central hypersomnia in DM1 (CNS-mediated, not solely from sleep apnea); improves alertness and quality of life	100 mg :: PO :: daily :: Start 100 mg PO every morning; may increase to 200 mg daily after 1-2 weeks; max 400 mg/day; avoid afternoon dosing to prevent insomnia	Hypersensitivity; severe hepatic impairment; cardiac arrhythmia (common in DM1 -- use with caution)	BP; heart rate; mood; insomnia; hepatic function; cardiac rhythm	-	ROUTINE	ROUTINE	-
Armodafinil	PO	Excessive daytime somnolence in DM1 if modafinil not tolerated; R-enantiomer with longer half-life	150 mg :: PO :: daily :: Start 150 mg PO every morning; may increase to 250 mg daily; avoid afternoon dosing	Hypersensitivity; severe hepatic impairment; cardiac arrhythmia	BP; heart rate; mood; insomnia; hepatic function; cardiac rhythm	-	ROUTINE	ROUTINE	-
Methylphenidate	PO	Excessive daytime somnolence refractory to modafinil; also helps apathy and cognitive sluggishness in DM1	5 mg :: PO :: BID :: Start 5 mg PO BID (morning and noon); increase by 5-10 mg/day weekly; max 60 mg/day; avoid evening dosing	Cardiac arrhythmia; severe hypertension; glaucoma; agitation; concurrent MAOI; tics/Tourette	BP; heart rate; ECG at baseline (cardiac conduction disease in DM1); appetite; weight; sleep; mood	-	ROUTINE	ROUTINE	-
CPAP or BiPAP	Device	Obstructive sleep apnea (OSA) and/or central hypoventilation from respiratory muscle weakness; very common in DM1	N/A :: Device :: nightly :: Titrate via sleep study; CPAP for OSA; BiPAP (with backup rate) preferred if central apnea or respiratory muscle weakness (FVC <60% predicted); use nightly	Intolerance (mask fitting, claustrophobia); pneumothorax	Compliance monitoring; repeat sleep study after titration; overnight oximetry; PaCO2 if hypoventilation	-	ROUTINE	ROUTINE	ROUTINE
Metformin	PO	Insulin resistance and type 2 diabetes mellitus in DM1; first-line oral hypoglycemic	500 mg :: PO :: daily :: Start 500 mg PO daily with meals; increase by 500 mg weekly; target 1000 mg BID; max 2550 mg/day; take with food	eGFR <30; metabolic acidosis; acute illness with risk of lactic acidosis; hold for contrast procedures	HbA1c q3 months; renal function q6-12 months; B12 annually (long-term use); lactic acidosis symptoms	-	ROUTINE	ROUTINE	-
Levothyroxine	PO	Hypothyroidism treatment in DM1 patients with confirmed thyroid dysfunction	25 mcg :: PO :: daily :: Start 25-50 mcg PO daily (lower dose in elderly or cardiac disease); titrate by 12.5-25 mcg q6-8 weeks based on TSH; take on empty stomach 30-60 min before breakfast	Untreated adrenal insufficiency; acute MI; thyrotoxicosis	TSH q6-8 weeks during titration; then q6-12 months when stable; heart rate; cardiac symptoms (arrhythmia risk in DM1)	-	ROUTINE	ROUTINE	-
Gabapentin	PO	Neuropathic pain or painful cramps; concurrent peripheral neuropathy in older DM patients	300 mg :: PO :: qHS :: Start 300 mg PO qHS; increase by 300 mg/day every 3-5 days; target 900-1800 mg/day divided TID; max 3600 mg/day; reduce dose if CrCl <60	Severe renal impairment (dose adjust); respiratory depression risk (caution in DM1 with respiratory muscle weakness)	Sedation; dizziness; fall risk; respiratory status; renal function	-	ROUTINE	ROUTINE	-
Pregabalin	PO	Neuropathic pain or muscle cramps if gabapentin not tolerated; concurrent pain conditions	75 mg :: PO :: BID :: Start 75 mg PO BID; may increase to 150 mg BID after 1 week; max 300 mg BID; reduce dose if CrCl <60	Severe renal impairment (dose adjust); angioedema history; respiratory depression risk (caution in DM1)	Sedation; dizziness; fall risk; respiratory status; peripheral edema; weight gain; renal function	-	ROUTINE	ROUTINE	-
Sertraline	PO	Depression and anxiety (common comorbidities in chronic progressive neuromuscular disease; adjustment disorder)	25 mg :: PO :: daily :: Start 25 mg PO daily; increase to 50 mg after 1 week; may titrate by 25-50 mg q2-4 weeks; max 200 mg/day	Concurrent MAOIs (14-day washout); concurrent pimozide	Suicidality monitoring (first 4 weeks); serotonin syndrome; hyponatremia (SIADH); QTc if high dose	-	ROUTINE	ROUTINE	-
Escitalopram	PO	Depression and anxiety in DM patients; alternative to sertraline	5 mg :: PO :: daily :: Start 5 mg PO daily; increase to 10 mg after 1 week; max 20 mg/day (10 mg in age >65 per FDA)	Concurrent MAOIs; QTc prolongation (particularly relevant given cardiac conduction risk in DM1)	QTc monitoring (essential in DM1); hyponatremia; suicidality monitoring	-	ROUTINE	ROUTINE	-
Docusate sodium	PO	Constipation prevention (GI dysmotility common in DM1; reduced activity; smooth muscle involvement)	100 mg :: PO :: BID :: 100 mg PO BID	GI obstruction	Bowel function	-	ROUTINE	ROUTINE	-
Polyethylene glycol (MiraLAX)	PO	Constipation (GI dysmotility from smooth muscle involvement in DM1; reduced physical activity)	17 g :: PO :: daily :: 17 g (1 capful) dissolved in 8 oz liquid PO daily; adjust frequency based on response	GI obstruction; bowel perforation	Bowel function; hydration status	-	ROUTINE	ROUTINE	-
Metoclopramide	PO	Gastroparesis and GI dysmotility in DM1; promotes gastric emptying	5 mg :: PO :: TID :: 5-10 mg PO 30 minutes before meals and at bedtime; max 40 mg/day; limit use to <12 weeks due to tardive dyskinesia risk	Parkinsonian symptoms; seizure disorder; GI obstruction; pheochromocytoma; concurrent use of drugs causing EPS	Tardive dyskinesia (limit duration); EPS; prolactin elevation; QTc prolongation	-	ROUTINE	ROUTINE	-
Trazodone	PO	Insomnia (sleep disruption common in DM1 from central mechanisms, pain, and respiratory issues)	25 mg :: PO :: qHS :: Start 25-50 mg PO qHS; may increase to 100 mg qHS; max 200 mg for insomnia	Concurrent MAOIs; QTc prolongation (cardiac conduction disease in DM1)	Sedation; orthostatic hypotension (fall risk); QTc monitoring; priapism (rare)	-	ROUTINE	ROUTINE	-
Testosterone cypionate (males)	IM	Symptomatic hypogonadism in DM1 males (fatigue, reduced libido, muscle wasting, osteoporosis); confirmed by low testosterone levels	200 mg :: IM :: q2 weeks :: Testosterone cypionate 200 mg IM q2 weeks; adjust dose based on trough levels; target total testosterone 400-700 ng/dL	Prostate cancer; breast cancer; polycythemia (Hct >54%); severe BPH; untreated sleep apnea (caution -- OSA common in DM1)	PSA and DRE at baseline and annually; hematocrit q3-6 months (polycythemia risk); testosterone trough levels; lipids; LFTs; bone density; sleep apnea symptoms	-	-	ROUTINE	-
Testosterone gel 1% (males)	TOP	Symptomatic hypogonadism in DM1 males (fatigue, reduced libido, muscle wasting, osteoporosis); alternative to IM injection; confirmed by low testosterone levels	50 mg :: TOP :: daily :: Testosterone gel 1% (50 mg) applied topically to shoulders/upper arms daily; avoid skin-to-skin transfer; adjust dose based on testosterone levels	Prostate cancer; breast cancer; polycythemia (Hct >54%); severe BPH; untreated sleep apnea (caution -- OSA common in DM1); skin-to-skin transfer risk to women/children	PSA and DRE at baseline and annually; hematocrit q3-6 months (polycythemia risk); testosterone levels; lipids; LFTs; bone density; sleep apnea symptoms; application site reactions	-	-	ROUTINE	-
Calcium carbonate + Vitamin D	PO	Bone health in DM patients at fall risk; vitamin D deficiency common and worsens muscle weakness; osteoporosis prevention	1000 mg Ca + 1000 IU D :: PO :: daily :: Calcium 1000-1200 mg + Vitamin D 1000-2000 IU PO daily; higher vitamin D doses if deficient (50,000 IU weekly x 8 weeks then maintenance)	Hypercalcemia; hyperparathyroidism; renal stones (relative)	Serum calcium; vitamin D level q3-6 months until replete; then annually	-	ROUTINE	ROUTINE	-

3C. Second-line/Refractory¶

Treatment	Route	Indication	Dosing	Contraindications	Monitoring	ED	HOSP	OPD	ICU
Carbamazepine	PO	Second-line for myotonia if mexiletine not tolerated or contraindicated; sodium channel blocker	100 mg :: PO :: BID :: Start 100 mg PO BID; increase by 100-200 mg/week; target 400-600 mg/day divided BID-TID; max 1200 mg/day	AV block (without pacemaker); bone marrow suppression; concurrent use with MAOIs; HLA-B*1502 positive (Stevens-Johnson risk in Southeast Asian descent)	CBC q2-4 weeks x 3 months then q3-6 months (agranulocytosis risk); LFTs; sodium (hyponatremia common); carbamazepine level (therapeutic 4-12 mcg/mL); ECG (cardiac conduction in DM1)	-	ROUTINE	ROUTINE	-
Phenytoin	PO	Second-line for myotonia if mexiletine and carbamazepine not tolerated; sodium channel blocker with antimyotonic properties	100 mg :: PO :: TID :: Start 100 mg PO TID; adjust based on levels; target level 10-20 mcg/mL; extended-release: 200-300 mg daily	AV block (without pacemaker); hypersensitivity; porphyria; cardiac conduction disease in DM1 (use with extreme caution)	Phenytoin level (therapeutic 10-20 mcg/mL); CBC; LFTs; calcium/vitamin D (chronic use depletes); ECG; gingival health; drug interactions (potent enzyme inducer)	-	EXT	EXT	-
Lamotrigine	PO	Alternative for myotonia refractory to mexiletine; limited evidence but sodium channel blocking mechanism	25 mg :: PO :: daily :: Start 25 mg PO daily x 2 weeks; then 50 mg daily x 2 weeks; then 100 mg daily; max 200-400 mg/day divided BID; SLOW titration to avoid SJS/TEN	Hypersensitivity; concurrent valproate (halve dose due to interaction); rash history with AEDs	Rash (Stevens-Johnson/TEN risk -- educate patient to stop immediately if rash develops); LFTs; renal function; suicidality monitoring	-	EXT	EXT	-
Acetazolamide	PO	Myotonia refractory to first-line agents; may improve myotonia through carbonic anhydrase inhibition; limited evidence	250 mg :: PO :: BID :: Start 250 mg PO BID; may increase to 250 mg TID; max 1000 mg/day	Severe hepatic or renal impairment; sulfonamide allergy; hyponatremia; hypokalemia; adrenal insufficiency	Electrolytes (hypokalemia, metabolic acidosis); renal function; paresthesias (common, benign); renal stones risk; CBC	-	EXT	EXT	-
Pacemaker or ICD implantation	Procedure	Cardiac conduction disease with symptomatic bradycardia, high-degree AV block, prolonged HV interval (>70 ms), or ventricular arrhythmia; lower threshold for device in DM1 given progressive conduction disease	N/A :: Procedure :: once :: Pacemaker for symptomatic bradycardia or high-degree AV block; ICD if sustained VT, VF, or high-risk features; cardiology-driven decision with lower threshold than general population given progressive conduction disease in DM1	Active infection; coagulopathy; patient refusal	Device interrogation q6-12 months; remote monitoring preferred; ECG annually; continued Holter monitoring as needed	-	URGENT	ROUTINE	-
Cataract surgery (phacoemulsification)	Surgical	Visually significant posterior subcapsular cataracts causing functional impairment; pathognomonic "Christmas tree" cataracts in DM1	N/A :: Surgical :: once per eye :: Phacoemulsification with IOL implant by ophthalmology; CRITICAL: anesthesia team must be aware of DM diagnosis -- malignant hyperthermia-like risk, avoid succinylcholine, prolonged recovery from sedation	Anesthesia risk (see anesthesia precautions); active ocular infection	Visual acuity post-operatively; IOP; posterior capsule opacification (higher rate in DM1); anesthesia recovery monitoring	-	ROUTINE	ROUTINE	-

3D. Disease-Modifying or Chronic Therapies¶

Treatment	Route	Indication	Dosing	Pre-Treatment Requirements	Contraindications	Monitoring	ED	HOSP	OPD	ICU
No proven disease-modifying therapy for DM1 or DM2	N/A	No FDA-approved disease-modifying treatment exists; multiple clinical trials ongoing (antisense oligonucleotides targeting DMPK mRNA, small molecules, CRISPR-based approaches); management is entirely supportive and symptomatic	N/A :: N/A :: N/A :: No disease-modifying therapy available; focus on multisystem monitoring, symptomatic management, cardiac surveillance, respiratory support, and rehabilitation	N/A	N/A	Monitor for emerging clinical trial opportunities; annual reassessment of functional status; reassess trial eligibility at each visit	-	-	ROUTINE	-

4. OTHER RECOMMENDATIONS¶

4A. Referrals & Consults¶

Recommendation	ED	HOSP	OPD	ICU
Neuromuscular specialist for diagnostic confirmation, genetic testing coordination, multisystem disease management, and longitudinal monitoring of DM1/DM2	URGENT	URGENT	ROUTINE	-
Cardiology for cardiac conduction abnormality assessment, annual ECG/Holter monitoring, pacemaker/ICD evaluation, and arrhythmia management (leading cause of sudden death in DM1)	URGENT	URGENT	ROUTINE	-
Pulmonology for respiratory function monitoring, sleep-disordered breathing evaluation, non-invasive ventilation titration, and management of respiratory muscle weakness	URGENT	ROUTINE	ROUTINE	URGENT
Ophthalmology for annual slit-lamp examination to monitor posterior subcapsular cataracts (>90% prevalence in DM1) and surgical planning when visually significant	-	ROUTINE	ROUTINE	-
Endocrinology for diabetes mellitus management, thyroid dysfunction treatment, hypogonadism evaluation and testosterone replacement, and metabolic syndrome optimization	-	ROUTINE	ROUTINE	-
Genetic counseling for autosomal dominant inheritance education, anticipation phenomenon explanation (earlier onset and increased severity in successive generations), family member testing, and reproductive planning	-	ROUTINE	ROUTINE	-
Speech-language pathology for swallow evaluation given oropharyngeal weakness and dysarthria risk in DM1; aspiration prevention strategies	URGENT	ROUTINE	ROUTINE	URGENT
Physical therapy for individualized exercise program (low-to-moderate intensity), gait training, fall prevention, and assistive device fitting given progressive weakness	-	ROUTINE	ROUTINE	-
Occupational therapy for ADL adaptation, hand function optimization (grip myotonia management), energy conservation, and home modification assessment	-	ROUTINE	ROUTINE	-
Anesthesiology pre-operative consultation REQUIRED before any surgical procedure; DM patients at high risk for malignant hyperthermia-like reactions, cardiac arrhythmias, prolonged recovery, respiratory failure; succinylcholine is CONTRAINDICATED	URGENT	URGENT	ROUTINE	URGENT
Gastroenterology for GI dysmotility evaluation, gastroparesis management, pseudo-obstruction assessment, and gallbladder disease screening (cholelithiasis common in DM1)	-	ROUTINE	ROUTINE	-
Psychiatry/Psychology for cognitive-behavioral assessment, depression/anxiety treatment, apathy management, and neuropsychological testing in DM1 (CNS involvement causes executive dysfunction and personality changes)	-	ROUTINE	ROUTINE	-
Social work for disability evaluation assistance, insurance navigation, community resources, vocational rehabilitation, and caregiver support	-	ROUTINE	ROUTINE	-
Physiatry (PM&R) for comprehensive rehabilitation planning, durable medical equipment prescription, orthotic fitting (AFOs for foot drop), and disability evaluation	-	ROUTINE	ROUTINE	-
Sleep medicine for excessive daytime somnolence evaluation, polysomnography interpretation, CPAP/BiPAP titration, and central hypersomnia management	-	ROUTINE	ROUTINE	-
Palliative care for goals of care discussion, symptom management optimization, advance care planning, and quality of life support in advanced disease	-	-	EXT	-

4B. Patient Instructions¶

Recommendation	ED	HOSP	OPD
Return to ED immediately if palpitations, lightheadedness, syncope, or near-syncope (may indicate cardiac arrhythmia or heart block -- leading cause of sudden death in DM1)	STAT	STAT	ROUTINE
Return to ED if new difficulty breathing, worsening shortness of breath, or morning headaches (may indicate respiratory muscle weakness or hypoventilation requiring ventilatory support)	STAT	STAT	ROUTINE
Return to ED if fall with head injury, inability to get up, or new severe pain (progressive weakness increases fall risk)	STAT	STAT	ROUTINE
Return to ED if choking during eating or drinking, inability to swallow medications, or recurrent coughing with meals (aspiration risk from oropharyngeal weakness)	STAT	STAT	ROUTINE
Return to ED if fever with cough or difficulty breathing (may indicate aspiration pneumonia given dysphagia risk)	STAT	STAT	ROUTINE
CRITICAL: Inform ALL healthcare providers and anesthesiologists of myotonic dystrophy diagnosis before ANY surgical or dental procedure; succinylcholine is CONTRAINDICATED; risk of malignant hyperthermia-like reaction, cardiac arrhythmia, and prolonged recovery from anesthesia	STAT	STAT	ROUTINE
Carry a medical alert bracelet or card identifying myotonic dystrophy diagnosis and "No Succinylcholine" warning for emergency situations	-	ROUTINE	ROUTINE
Use assistive devices as recommended by PT/OT (AFOs for foot drop, cane, walker) to prevent falls; early adoption improves safety	-	ROUTINE	ROUTINE
Expect slow but progressive weakness over years; DM is a chronic condition without cure, but proactive multisystem monitoring significantly improves quality of life and prevents complications	-	ROUTINE	ROUTINE
Attend annual cardiac monitoring (ECG and Holter) even if asymptomatic; conduction abnormalities can develop without symptoms and cause sudden cardiac death	-	ROUTINE	ROUTINE
Report new or worsening daytime sleepiness, snoring, or morning headaches to neurology (may indicate sleep apnea or hypoventilation requiring CPAP/BiPAP)	-	ROUTINE	ROUTINE
Do not drive if excessive daytime somnolence or cardiac arrhythmia is present; discuss driving safety with neurology	-	ROUTINE	ROUTINE
Inform family members that myotonic dystrophy is inherited (autosomal dominant); children have a 50% chance of inheriting the condition; genetic counseling available for family planning	-	ROUTINE	ROUTINE
Be aware of anticipation: children (especially those inheriting from mother) may develop more severe, earlier-onset disease; genetic counseling and prenatal testing are available	-	ROUTINE	ROUTINE

4C. Lifestyle & Prevention¶

Recommendation	ED	HOSP	OPD
Low-to-moderate intensity exercise program (walking, swimming, stationary cycling) 3-5 days per week to maintain cardiovascular fitness and slow deconditioning; avoid extreme exertion which may worsen weakness	-	ROUTINE	ROUTINE
High-protein diet (1.0-1.5 g/kg/day protein) to support muscle preservation; adequate caloric intake to prevent weight loss from dysphagia or GI dysmotility	-	ROUTINE	ROUTINE
Home safety evaluation by OT to remove fall hazards, install grab bars, raised toilet seat, shower bench, stair rails, and adequate lighting given progressive weakness and fall risk	-	ROUTINE	ROUTINE
Annual influenza vaccination (inactivated) and pneumococcal vaccination per guidelines given respiratory muscle weakness and aspiration risk	-	ROUTINE	ROUTINE
Strict glycemic control (HbA1c <7%) to prevent diabetic complications and neuropathy progression in DM patients with insulin resistance or diabetes	-	ROUTINE	ROUTINE
Alcohol limitation as alcohol worsens respiratory depression, increases fall risk, exacerbates hepatic dysfunction, and interacts with CNS-depressant medications	-	ROUTINE	ROUTINE
Smoking cessation to reduce respiratory infection risk and improve pulmonary function (already compromised by respiratory muscle weakness)	-	ROUTINE	ROUTINE
CPAP/BiPAP compliance essential for patients with sleep-disordered breathing to prevent nocturnal hypoxia, morning headaches, and daytime somnolence	-	ROUTINE	ROUTINE
Adequate sleep hygiene (consistent schedule, 7-9 hours) to manage DM1-related hypersomnia; avoid sedating medications when possible	-	ROUTINE	ROUTINE
Weight management to reduce metabolic burden and improve mobility; obesity worsens insulin resistance and respiratory function in DM	-	ROUTINE	ROUTINE
Vitamin D supplementation to maintain level >30 ng/mL for muscle and bone health; higher dose repletion if deficient	-	ROUTINE	ROUTINE
Fall prevention program including balance exercises, home modifications, medication review for fall-risk-increasing medications, and vision correction (cataracts)	-	ROUTINE	ROUTINE
Advance care planning discussion including code status, ventilatory support preferences, and goals of care early in disease course while patient can fully participate in decision-making	-	ROUTINE	ROUTINE

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

5. DIFFERENTIAL DIAGNOSIS¶

Alternative Diagnosis	Key Distinguishing Features	Tests to Differentiate
Myotonia congenita (Thomsen/Becker disease)	Non-dystrophic myotonia; pure myotonia WITHOUT progressive weakness or systemic features; onset in childhood; muscle hypertrophy rather than atrophy; no cardiac involvement; no cataracts; CLCN1 gene mutation	Genetic testing (CLCN1 mutation; negative DMPK/CNBP); EMG (myotonic discharges but no myopathic MUAPs); no systemic features; normal cardiac evaluation
Paramyotonia congenita	Cold-induced myotonia (paradoxical -- worsens with repeated activity unlike classic myotonia); episodic weakness; SCN4A gene mutation; no progressive weakness or systemic involvement	Genetic testing (SCN4A mutation); cold provocation test; EMG with cooling; no systemic features; no cataracts; normal cardiac evaluation
Polymyositis	Symmetric proximal weakness; subacute onset; higher CK (10-50x ULN); NO myotonia; responsive to immunotherapy; no cataracts; no cardiac conduction disease; no genetic basis	CK (much higher); EMG (irritable myopathy WITHOUT myotonic discharges); muscle biopsy (endomysial CD8+ invasion without rimmed vacuoles); myositis-specific antibodies; steroid response
Inclusion body myositis (IBM)	Onset >50 years; finger flexor and quadriceps weakness pattern; NO myotonia; poor response to immunotherapy; rimmed vacuoles on biopsy; anti-cN1A antibody	EMG (mixed myopathic/neurogenic WITHOUT myotonic discharges); anti-cN1A antibody; muscle biopsy (rimmed vacuoles, amyloid deposits); no genetic trinucleotide repeat expansion
Limb-girdle muscular dystrophy (LGMD)	Progressive proximal weakness; NO myotonia; variable CK elevation; no systemic features (no cataracts, no cardiac conduction disease, no diabetes); specific genetic subtypes	Genetic testing panel (>30 subtypes); no myotonic discharges on EMG; no trinucleotide repeat expansion; muscle biopsy (dystrophic changes, specific protein deficiencies)
Motor neuron disease (ALS)	Upper AND lower motor neuron signs; fasciculations; NO myotonia; no systemic features; rapid progression; bulbar onset with dysarthria common	EMG (widespread denervation, fasciculations, NO myotonic discharges); no cardiac or endocrine involvement; no cataracts; no genetic trinucleotide repeat
Hypothyroid myopathy	Proximal weakness; fatigue; delayed relaxation of reflexes (may mimic myotonia clinically); elevated CK; reversible with thyroid replacement; no true electrical myotonia on EMG	TSH (elevated); free T4 (low); EMG (no myotonic discharges -- delayed relaxation is not electrical myotonia); CK normalizes with treatment; no genetic testing needed
Drug-induced myotonia (statins, colchicine, chloroquine)	Temporal correlation with drug exposure; myalgia and weakness; may have myotonic features on EMG; improves with drug discontinuation; no systemic features	Medication history; improvement after drug withdrawal; negative genetic testing for DM1/DM2; no cataracts or cardiac conduction disease
Schwartz-Jampel syndrome	Childhood onset; continuous muscle stiffness (not true myotonia); short stature; blepharospasm; skeletal abnormalities; HSPG2 gene mutation	Genetic testing (HSPG2); childhood onset; skeletal features; EMG (high-frequency discharges but not classic myotonic discharges); no systemic features of DM
Brody myopathy	Exercise-induced muscle stiffness (silent contractures -- no electrical activity on EMG); ATP2A1 gene mutation; no percussion myotonia; no systemic features	EMG (electrically silent contractures -- NO myotonic discharges); genetic testing (ATP2A1); no cataracts; no cardiac conduction disease
Late-onset Pompe disease	Proximal weakness; respiratory muscle weakness disproportionate to limb weakness; mildly elevated CK; NO myotonia; autosomal recessive	Acid alpha-glucosidase activity (reduced); GAA gene testing; EMG (myopathic without myotonic discharges in most -- some rare cases show myotonic discharges); no cardiac conduction disease

6. MONITORING PARAMETERS¶

Parameter	Frequency	Target/Threshold	Action if Abnormal	ED	HOSP	OPD	ICU
ECG (12-lead)	Annually minimum; more frequently if conduction abnormalities present; at any new cardiac symptom	Normal sinus rhythm; PR <200ms; QRS <120ms; no bundle branch block; no atrial fibrillation	If new conduction abnormality: urgent cardiology referral; Holter monitor; consider EPS; pacemaker/ICD evaluation; PR >240ms or HV >70ms warrants device consideration	STAT	STAT	ROUTINE	STAT
24-hour Holter monitor	Annually in DM1; q2-3 years in DM2 if asymptomatic; more frequently if abnormal	Normal rhythm; no pauses >2.5 sec; no high-degree AV block; no VT; no symptomatic arrhythmia	If significant arrhythmia: electrophysiology study; pacemaker/ICD evaluation; antiarrhythmic consideration (but most are contraindicated in DM1)	-	ROUTINE	ROUTINE	-
Pulmonary function tests (FVC, MIP, MEP)	Annually; q6 months if FVC <70% predicted or symptoms	FVC >80% predicted; MIP >60 cm H2O; MEP >40 cm H2O	If FVC declining or <60%: pulmonology referral; sleep study; BiPAP initiation; discuss advance care planning if FVC <40%	-	ROUTINE	ROUTINE	-
Slit-lamp ophthalmologic exam	Annually	No visually significant cataracts	If cataracts progressing and visually significant: ophthalmology surgical planning with anesthesia precautions; correct refractive error	-	-	ROUTINE	-
HbA1c	Annually if normal; q3-6 months if diabetic or prediabetic	<5.7% (normal); <7.0% (diabetic target)	If prediabetes: lifestyle modification, metformin consideration; if diabetes: initiate or optimize treatment; endocrinology referral	-	ROUTINE	ROUTINE	-
TSH	Annually	0.4-4.0 mIU/L	If elevated: confirm with free T4; initiate levothyroxine; recheck q6-8 weeks; endocrinology referral if complex	-	ROUTINE	ROUTINE	-
Testosterone (males)	Annually in symptomatic males; at diagnosis	Total testosterone >300 ng/dL	If low with symptoms: endocrinology referral; testosterone replacement; monitor PSA and hematocrit	-	ROUTINE	ROUTINE	-
Liver function tests (ALT, GGT)	Annually; q6 months if on hepatotoxic medications	Normal or stable mild elevation; GGT often elevated in DM1 at baseline	If progressive elevation: hepatology referral; abdominal ultrasound; reassess medications; fatty liver common in DM1	-	ROUTINE	ROUTINE	-
Muscle strength (MMT) and functional assessment	Every clinic visit; q6-12 months formal assessment	Stable or slowly declining; document MRC grades for key muscles; timed tests (6MWT, TUG)	If accelerated decline: reassess for superimposed conditions; optimize rehabilitation; adjust assistive devices	-	ROUTINE	ROUTINE	-
Swallowing function	Each clinic visit clinical screening; MBSS if symptomatic	Safe oral intake; no aspiration	If worsening dysphagia: SLP re-evaluation; diet modification; MBSS; aspiration precautions; consider PEG if severe	URGENT	ROUTINE	ROUTINE	URGENT
Depression/anxiety screening (PHQ-9)	Annually minimum; more frequently if concerns	PHQ-9 score <5 (minimal)	If PHQ-9 >=10: assess safety; initiate antidepressant; psychology/psychiatry referral	-	ROUTINE	ROUTINE	-
Sleep quality assessment (Epworth Sleepiness Scale)	Annually; more frequently if EDS or OSA present	ESS score <10 (normal)	If ESS >=10: sleep study; CPAP/BiPAP evaluation; modafinil consideration; sleep hygiene review	-	ROUTINE	ROUTINE	-
Bone density (DEXA)	Baseline; q2 years; sooner if fracture or steroid exposure	T-score >-1.0 (normal); >-2.5 (osteopenia acceptable)	If T-score <-2.5: bisphosphonate; calcium/vitamin D optimization; endocrine referral; fall prevention critical	-	-	ROUTINE	-
Weight and nutritional status	Each clinic visit	Stable weight; BMI 18.5-30; adequate caloric and protein intake	If weight loss >5% in 6 months: reassess dysphagia; nutrition consultation; calorie supplementation; GI evaluation	-	ROUTINE	ROUTINE	-

7. DISPOSITION CRITERIA¶

Disposition	Criteria
Discharge home	Ambulatory (with or without assistive device); safe swallow; adequate oral intake; cardiac rhythm stable (no new conduction abnormality requiring monitoring); pain controlled; respiratory status stable; outpatient neuromuscular and cardiology follow-up arranged; home safety adequate; understands return precautions and anesthesia warnings
Admit to floor	Fall-related injury requiring monitoring (fracture, head injury); aspiration pneumonia requiring IV antibiotics; new cardiac conduction abnormality requiring telemetry monitoring; new diagnosis requiring expedited inpatient workup; severe dehydration or malnutrition from dysphagia; respiratory decompensation not requiring ICU; pre-operative optimization for urgent surgery
Admit to ICU	Respiratory failure from aspiration pneumonia or respiratory muscle weakness requiring mechanical ventilation or non-invasive ventilation; hemodynamically significant arrhythmia (complete heart block, sustained VT); post-anesthesia prolonged respiratory depression or malignant hyperthermia-like reaction; cardiac arrest from conduction disease
Transfer to higher level of care	Need for neuromuscular specialist not available locally; electrophysiology study and pacemaker/ICD implantation not available on-site; cardiac MRI not available; genetic counseling services unavailable
Inpatient rehabilitation	Significant functional decline with deconditioning; post-fall with functional decline; able to participate in 3 hours/day therapy; medically stable; benefit expected from intensive PT/OT

8. EVIDENCE & REFERENCES¶

Recommendation	Evidence Level	Source
Myotonic dystrophy clinical practice guidelines (comprehensive)	Expert consensus	Ashizawa T et al. Neurology 2018 (AAN Practice Guideline)
DM1 genetics: CTG trinucleotide repeat expansion on DMPK gene (chromosome 19)	Class II, Level A	Brook JD et al. Cell 1992
DM2 genetics: CCTG tetranucleotide repeat expansion on CNBP/ZNF9 gene (chromosome 3)	Class II, Level A	Liquori CL et al. Science 2001
Anticipation in DM1: progressive expansion of CTG repeats across generations with earlier onset and greater severity	Class II, Level B	Harley HG et al. Nature 1993
Cardiac conduction abnormalities as leading cause of mortality in DM1	Class II, Level B	Groh WJ et al. NEJM 2008
ECG abnormalities predict sudden cardiac death in DM1; PR >200ms and QRS >100ms identify high-risk patients	Class II, Level B	Groh WJ et al. NEJM 2008
Prophylactic pacemaker implantation in DM1 with conduction abnormalities	Class III, Level C	Wahbi K et al. JAMA 2012
Mexiletine for myotonia in DM1 and non-dystrophic myotonia	Class I, Level B	Logigian EL et al. Neurology 2010
Mexiletine reduces myotonia in myotonic dystrophy: randomized controlled trial	Class I, Level B	Stunnenberg BC et al. Brain 2018 (MYOMEX trial)
Modafinil for excessive daytime somnolence in DM1	Class II, Level B	Talbot K et al. Neurology 2003
Respiratory involvement in myotonic dystrophy: diaphragmatic weakness, restrictive pattern, sleep-disordered breathing	Class II, Level B	Boussaid G et al. Neuromuscul Disord 2020
Sleep-disordered breathing and central hypersomnia in DM1	Class II, Level C	Laberge L et al. Neurology 2013
Insulin resistance and diabetes in DM1	Class II, Level B	Moxley RT et al. J Clin Invest 1984
Gastrointestinal dysmotility in myotonic dystrophy	Class II, Level C	Hilbert JE et al. Curr Gastroenterol Rep 2017
Anesthesia complications in myotonic dystrophy: malignant hyperthermia-like reactions, succinylcholine contraindicated	Class II, Level C	Mathieu J et al. Can J Anaesth 1997
Posterior subcapsular cataracts in myotonic dystrophy: pathognomonic "Christmas tree" cataracts	Class II, Level B	Baig KM et al. Saudi J Ophthalmol 2020
Cognitive and behavioral involvement in DM1: executive dysfunction, apathy, social cognition deficits	Class II, Level B	Minnerop M et al. Neurology 2011
DM2 (PROMM): clinical features, proximal weakness predominance, milder phenotype than DM1	Class II, Level B	Day JW et al. Neurology 2003
Myotonic dystrophy multisystem management consensus recommendations	Expert consensus	Bird TD. GeneReviews. University of Washington 2021
Natural history of DM1: functional decline and survival data	Class II, Level B	Mathieu J et al. Neurology 1999
Exercise safety and modest benefit in myotonic dystrophy	Class II, Level C	Orngreen MC et al. Neurology 2005
Hypogonadism in DM1 males: testicular atrophy, reduced testosterone, infertility	Class II, Level B	Peric S et al. Acta Myol 2018
Genetic counseling and anticipation in autosomal dominant myotonic dystrophy	Expert consensus	Harper PS. Myotonic Dystrophy. 3rd ed. WB Saunders 2001
Carbamazepine and phenytoin as second-line agents for myotonia	Class III, Level C	Trip J et al. Brain 2006

CHANGE LOG¶

v1.1 (January 31, 2026) - Standardized all structured dosing to 4-field :: format (dose :: route :: frequency :: full_instructions) across Sections 3A, 3B, 3C for clickable order sentences - Fixed starting dose in field 1 to single dose (not multiple dose levels) for all medications - Added ICU setting to frontmatter (was missing despite ICU-relevant content in Section 7) - Added ICU coverage to Section 1A core labs (CK, CMP, CBC, glucose, LFTs, Mg, Ca, UA) for ICU-admitted patients - Added ICU coverage to Section 1C specialized labs (BNP, troponin, ABG/SpO2) - Added ICU coverage to Section 2A imaging (ECG, CXR) and 2B (echocardiogram) - Added ICU coverage to Section 3A acute treatments (IV fluids, acetaminophen, antibiotics, DVT prophylaxis) for patients admitted to ICU with respiratory failure or post-anesthesia complications - Added ICU coverage to CPAP/BiPAP in Section 3B - Split testosterone replacement into two separate rows (testosterone cypionate IM and testosterone gel 1% topical) for distinct order sentences - Fixed acetaminophen structured dosing (was missing frequency field) - Fixed sertraline dosing field 1 to reflect starting dose (25 mg, not 50 mg) - Fixed escitalopram dosing field 1 to reflect starting dose (5 mg, not 10 mg) - Fixed trazodone dosing field 1 to reflect starting dose (25 mg, not 50 mg) - Added ICU to Section 4A referrals: Pulmonology (URGENT), SLP (URGENT), Anesthesiology (URGENT) - Added ICU coverage to Section 6 monitoring: ECG (STAT), swallowing function (URGENT) - Added DVT prophylaxis ICU coverage (ROUTINE) for immobilized ICU patients

v1.0 (January 30, 2026) - Initial template creation - Section 1: 29 laboratory tests across 3 tiers - 1A: 12 core labs (CK, CMP, CBC, glucose, HbA1c, TSH, free T4, LFTs, magnesium, calcium, lipids, UA) - 1B: 11 extended labs (genetic testing DM1/DM2, testosterone, FSH/LH, estradiol, insulin, immunoglobulins, GGT, vitamin D, iron studies, coagulation) - 1C: 6 rare/specialized (expanded myotonia genetic panel, myositis antibodies, Pompe enzyme, BNP, troponin, ABG/SpO2) - Section 2: Imaging and studies across 3 tiers - 2A: ECG, EMG/NCS, CXR, slit-lamp exam - 2B: Holter monitor, echocardiogram, PFTs, MIP/MEP, polysomnography, MRI brain, MBSS, MRI thighs - 2C: Cardiac MRI, EPS, muscle biopsy, neuropsychological testing, gastric emptying study - Section 3: Treatment across 4 subsections - 3A: 6 acute/emergent items (IV fluids, acetaminophen, aspiration pneumonia antibiotics, DVT prophylaxis) - 3B: 18 symptomatic treatments (mexiletine, modafinil, armodafinil, methylphenidate, CPAP/BiPAP, metformin, levothyroxine, gabapentin, pregabalin, sertraline, escitalopram, docusate, MiraLAX, metoclopramide, trazodone, testosterone, calcium/vitamin D) - 3C: 6 second-line/refractory (carbamazepine, phenytoin, lamotrigine, acetazolamide, pacemaker/ICD, cataract surgery) - 3D: No proven disease-modifying therapy acknowledgment - Section 4: Recommendations across 3 subsections - 4A: 16 referrals (neuromuscular, cardiology, pulmonology, ophthalmology, endocrinology, genetic counseling, SLP, PT, OT, anesthesiology, GI, psychiatry, social work, physiatry, sleep medicine, palliative care) - 4B: 14 patient instructions (return precautions, anesthesia warnings, medical alert, anticipation counseling) - 4C: 13 lifestyle/prevention recommendations - Section 5: 11 differential diagnoses (myotonia congenita, paramyotonia congenita, PM, IBM, LGMD, ALS, hypothyroid, drug-induced, Schwartz-Jampel, Brody myopathy, Pompe) - Section 6: 15 monitoring parameters with venue-specific coverage - Section 7: 5 disposition criteria levels - Section 8: 24 evidence citations with PubMed links

APPENDIX A: ANESTHESIA PRECAUTIONS IN MYOTONIC DYSTROPHY¶

CRITICAL SAFETY INFORMATION -- Share with ALL anesthesia and surgical teams

Contraindicated Agents¶

Agent	Risk	Alternative
Succinylcholine	CONTRAINDICATED -- causes severe, prolonged myotonic contracture unresponsive to neuromuscular blockade reversal; may cause masseter spasm and impossible intubation; hyperkalemia risk	Non-depolarizing agents (rocuronium, vecuronium, cisatracurium) at reduced doses
Volatile anesthetics (halothane, sevoflurane, isoflurane, desflurane)	Malignant hyperthermia-LIKE reactions (not true MH but clinically similar); prolonged recovery; respiratory depression; cardiac arrhythmia	Total intravenous anesthesia (TIVA) with propofol and remifentanil preferred
Neostigmine (high dose)	Anticholinesterase reversal agents can precipitate myotonic crisis and profound bradycardia in DM1	Sugammadex for rocuronium reversal (preferred); minimal neostigmine if absolutely necessary

Perioperative Management¶

Phase	Key Considerations
Pre-operative	ECG and cardiac clearance; PFTs if not recent; anesthesia consult mandatory; discuss ventilatory support plan; document genetic type (DM1 vs DM2 -- DM1 higher risk)
Intra-operative	Avoid succinylcholine; TIVA preferred; reduced doses of non-depolarizing agents; temperature monitoring; avoid hypothermia (worsens myotonia); cardiac monitoring throughout
Post-operative	Prolonged PACU monitoring (minimum 24-48 hours for major surgery); delayed extubation is common; respiratory monitoring (pulse oximetry, capnography); avoid opioids or use minimal doses with close monitoring; aspiration precautions

Emergency Situations¶

If malignant hyperthermia-like reaction: treat per MH protocol (dantrolene 2.5 mg/kg IV, cooling measures) even though not true MH
If myotonic crisis (sustained myotonic contracture): IV mexiletine if available; warm IV fluids; avoid triggering agents; supportive care
If cardiac arrest: standard ACLS protocol; be aware that standard antiarrhythmics may be less effective; early pacing for bradycardia

APPENDIX B: DM1 vs DM2 COMPARISON¶

Feature	DM1 (Steinert Disease)	DM2 (PROMM)
Genetics	CTG repeat expansion, DMPK gene, chromosome 19q13.3	CCTG repeat expansion, CNBP (ZNF9) gene, chromosome 3q21.3
Inheritance	Autosomal dominant with anticipation	Autosomal dominant; minimal or no anticipation
Congenital form	Yes (severe, maternal transmission)	No congenital form
Weakness pattern	Distal > proximal (grip, ankle dorsiflexion, facial, neck flexors)	Proximal > distal (hip flexors, quadriceps, neck flexors)
Myotonia	Prominent (grip, percussion, jaw)	Variable; often milder; pain more prominent than stiffness
Cardiac	Severe conduction disease; arrhythmias; sudden death risk (25-30% of deaths)	Less severe; conduction abnormalities occur but less frequent
Cataracts	>90%; posterior subcapsular "Christmas tree"	Common; posterior subcapsular but less distinctive
CNS involvement	Significant: executive dysfunction, apathy, hypersomnia, white matter changes	Milder cognitive involvement
Diabetes/insulin resistance	25-75%	Present but less common
GI involvement	Significant dysmotility, dysphagia, pseudo-obstruction	Milder GI involvement
Respiratory	Diaphragmatic weakness; central + obstructive sleep apnea; hypoventilation	Less severe respiratory involvement
Severity	Generally more severe; earlier onset with larger repeats	Generally milder; later onset (mean 40-50 years)
Life expectancy	Reduced (mean 50-60 years in classic DM1)	Near-normal in many patients
Myalgia	Less prominent	More prominent (can be presenting symptom)