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