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Myotonic dystrophy
Myotonic dystrophy type 1 is a multisystem genetic disease (CTG repeat expansion in the DMPK gene) that combines distal and facial weakness with myotonia — difficulty releasing a grip — plus cataract, cardiac conduction disease, insulin resistance and sensitivity to anaesthetic drugs.
Why it matters in the exam
The classic scenario is a young adult with a long thin face, drooping lids, frontal balding, hand weakness and a grip he cannot release after a handshake. The tests check inheritance (autosomal dominant with anticipation, and especially a severe congenital form when the mother transmits it), cardiac involvement (conduction disease and sudden death, so regular ECG and sometimes a pacemaker), cataract, anaesthetic implications (sensitivity to opioids and sedatives, avoiding suxamethonium), and the EMG with myotonic discharges. Common distractors are thinking of myasthenia because of the ptosis, or forgetting that the heart, eyes and endocrine system are part of the disease. Type 2 is milder, proximal, and has no congenital form. Relatives without obvious symptoms may also carry the disease.
Key points
- Myotonic dystrophy type 1 is caused by CTG repeat expansion in DMPK and is dominantly inherited with anticipation.
- Distal and facial weakness with myotonia — difficulty releasing a grip.
- The heart is involved with conduction disease and sudden death: ECG at least once a year.
- Cataract, insulin resistance, hypogonadism and sleepiness are part of the disease.
- Sensitivity to anaesthetic drugs; the congenital form is passed mainly from the mother.
Summary table
| System | Feature | What to do |
|---|---|---|
| Muscles | Distal, facial and neck weakness; grip and percussion myotonia | Mexiletine for troublesome myotonia; EMG with myotonic discharges |
| Heart | Conduction disease, arrhythmias and sudden death | ECG at least once a year, Holter; pacemaker or defibrillator according to findings |
| Eyes and endocrine | Posterior subcapsular cataract, insulin resistance, hypogonadism, frontal balding | Regular eye and glucose checks |
| Breathing, swallowing and sleep | Respiratory muscle weakness, swallowing difficulty, excessive daytime sleepiness | Respiratory follow-up; non-invasive ventilation as needed |
| Genetics and pregnancy | Autosomal dominant with anticipation; maternal transmission — congenital form with a floppy newborn; polyhydramnios | Genetic counselling; high-risk pregnancy care |
| Anaesthesia | Sensitivity to opioids, benzodiazepines and anaesthetics; risk of respiratory failure after surgery | Avoid suxamethonium; prolonged post-operative monitoring |
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Sources
- Consensus-Based Care Recommendations for Adults With Myotonic Dystrophy Type 1 (Ashizawa et al., Neurology: Clinical Practice), 2018 — Cardiac, respiratory, anaesthetic and ocular care
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.