Dystrophia myotonica

Myotonic dystrophy is the most common muscular dystrophy and is characterised by myotonia and muscular atrophy.

Inheritance is autosomal dominant. The incidence is 5 per 100 000 with onset between 15 and 40 years, although it may present as early as birth. The causal gene is on chromosome 19.

The disease is slowly progressive and is characterised by cataract formation, hypogonadism, frontal balding and cardiac disorders. There is weakness, wasting and myotonia of involved muscles. Wasting of the stenocleidomastoids produces the classical swan-necked appearance.

The condition reduces longevity.

Notes:

• the prevalence of myotonic dystrophy varies with respect to different populations. However, in a study of neuromuscular disease in Northern Ireland, myotonic dystrophy was found to have the highest prevalence (1)

Reference:

1. Hicks MI et al. The prevalence of inherited neuromuscular disease in Northern Ireland.Neuromuscul Disord. 1996 Jan;6(1):69-73.