Muscular dystrophies - myotonic dystrophy
Description
- Multisystem AD disorder: myotonia + distal weakness + cataracts + conduction disease + endocrine failure
- Myotonia = involuntary contraction continuing after voluntary effort ceases -> impaired relaxation
- Grip myotonia (delayed handshake release); percussion myotonia (thenar eminence)
- Warms up with repetition - opposite of paramyotonia congenita (worsens with repetition + cold)
DM1 vs DM2
| DM1 (Steinert) | DM2 (PROMM) | |
|---|---|---|
| Gene / repeat | DMPK 19q13, CTG | CNBP (ZNF9) 3q21, CCTG |
| Weakness | Distal > proximal; face, neck | Proximal (hip girdle); myalgia prominent |
| Anticipation | Marked | Minimal |
| Congenital form | Yes - almost always maternal | No |
| Course | Earlier, more severe | Milder, near-normal lifespan |
- One of the few myopathies with distal-predominant weakness
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