EpistemisMyotonia
Specialty: Neurology.
Why it occurs
- Myotonic dystrophy type 1 (Steinert disease, autosomal dominant)
- Myotonic dystrophy type 2 (PROMM or proximal myotonic myopathy)
- Myotonia congenita (Thomsen or Becker disease, chloride channelopathies)
- Paramyotonia congenita (cold-sensitive sodium channelopathy)
- Myotonia induced by drugs or toxic substances (statin-type cholesterol in rare cases with genetic predisposition)
Initial workup
Clinical evidence of grip myotonia (inability of the patient to open the hand quickly after a firm grip) and percussion myotonia (contraction and persistence of the muscular labrum after hitting the thenar eminence or tongue with the hammer); electromyography (EMG) to objectify characteristic myotonic discharges ("dive bomber" sound in the EMG speaker); genetic study to confirm nucleotide expansion (CTG in the DMPK gene for Steinert); electrocardiogram and 24-hour Holter.
red flags
Presence of myotonia associated with severe cardiac arrhythmias (complete atrioventricular block, ventricular tachyarrhythmias), progressive restrictive respiratory failure or severe dysphagia with frequent episodes of choking, typical of the systemic progression of Steinert Dystrophy.
Standard management
- Mexiletine — 150-600 mg/day, sodium channel blocker, considered the treatment of choice to reduce the myotonic phenomenon, contraindicated in the presence of cardiac conduction blocks
- Carbamazepine — 200-600 mg/day
- Phenytoin
- Preventive cardiac pacing if significant conduction disorders are detected in the electrocardiogram.
Educational guidance for study. It is NOT a prescription recommendation. The actual choice depends on the cause, the patient, and current guidelines.
- Area
- Neurology
- Listed causes
- 5
- Treatment options
- 4