Proximal spinal muscular atrophy.

It has been known for some time that cases of muscular atrophy can occur in young people which clinically resemble limb girdle muscular dystrophy but which electromyographically and histologically can be shown to be due to damage to the spinal motor neurone. Investigation of the family frequently reveals further cases, and the course and prognosis is often benign and relatively non-progressive and similar in many ways to the course of limb-girdle muscular dystrophy. Similar cases occurring in a slightly older age group are likely to be confused with motor neurone disease, and thus given an unnecessarily poor prognosis. It is not until they are seen to survive much longer than would be expected and their disorder remain confined to the lower motor neurone, that it becomes evident that one may be dealing with a different condition. Three cases are recorded here which have many similarities clinically, electromyographically, and histologically; the first two started in late adolescence and were initially thought to have the clinical features of muscular dystrophy, and the third case started in middle age and was for many years thought to be motor neurone disease.