Myotonia Congenita

A form of nondystrophic myotonia

Synonyms:

a.k.a. Thomsen’s disease

Clinical features:

1st and 2nd decade
When infant: inability to open eyes after face is washed, peculiar cry
Muscular hypertrophy (generalized), myotonia (worse in cold),
No weakness
Warm up phenomenon: improved strength and movement after warm up

Genetics:

  • Autosomal dominant
  • Genetic analysis: chloride channel CLCN1 gene mutations on chromosome 7. Different mutations for each.

Muscle biopsy:

  • Variation in fibre size. Rare centronucleation. Type 2A fibre hypertrophy. Type 2B fibres may be absent.

Findings on investigations:

EMG:

  • Myotonia

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