Friday 15 October 2010

MRCP revision battle 30.3: Myotonic Dystrophy

Myotonic dystrophy is an autosomal dominant condition in which there is muscle weakness and myotonia.  It is a trinucleotide repeat disorder.

Onset tends to be in the 30s.


There are 2 types:


Dystrophia myotonica (=DM) 1
  • 98% of cases
  • more severe
  • distal muscle weakness
  • chromosome 19
Dystrophia myotonica 2:
  • 2% of cases
  • less severe
  • proximal muscle weakness
  • chromosome 3

Features associated with myotonic dystrophy include:
  • long faces
  • frontal baldness
  • myotonia and weakness
  • testicular/ovarian atrophy
  • bilateral ptosis
  • cateract
  • cardiomyopathy
  • diabetes
  • miotic pupils 
  • mildly decreased IQ

It is incurable but phenytoin can improve the myotonia.


Lets move on to consider an overview of trinucleotide repeat disorders