Synonyms:
a.k.a. Dystrophia myotonica a.k.a. DM a.k.a. DM1 a.k.a. Steinert disease
Diagnosis:
Clinical +EMG +consistent labs
Clinical features:
Early frontal baldness,
Wasting of temporalis (hatchet face), massester and sternocleidomastoid (swan neck),
Ptosis, facial weakness. Weakness and atrophy of distal arms and finger flexors, and quadriceps and tibialis anterior (foot drop)
Decreased reflexes
Myotonia: difficulty releasing hand grip, percussion myotonia,
+cataracts
Findings on investigations:
CK: normal or slightly high
EMG:
- Evidence of myotonia
ECG:
- Conduction abnormalities
Muscle Biopsy:
Non-grouped Atrophy, nuclear bags. Centronucleation. NADH: Striated annulets ‘ringbinden’. Ring fibres. Usually no or mild necrosis or excess connective tissue. Atrophy of type 1 fibres
Electron microscopy: myofibrils at the periphery perpendicular to the central portion
Genetics:
CTG repeat expansion in DM protein kinase DMPK on chromosome 19
Treatment:
Treat cardiac conduction abnormalities
Symptomatic for myotonia with:
- 1st line: Phenytoin PHT
- 2nd line: may worsen conduction abnormalities quinine sulphate tid, procainamide qid
Orthoses
Genetic counselling