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.
Last reviewed 01/2018