The hands are first affected with weakness of finger extensor muscles. In the lower extremity it is mainly the anterior tibial muscle that is affected. Cardiac involvement is never seen. Progression rate is very slow, anticipation is not detected and life-span is not shortened. Histopathological changes in muscle biopsies are mainly of myopathic type and include rimmed vacuoles.
Neurophysiological findings are of both myopathic and neuropathic type.
The clinical features of the disorder were analysed with patient examinations, quantitative sensory testing, histopathology, neurophysiology and magnetic resonance imaging of the musculature. This presents as a sensory dysfunction in the distal parts of upper and lower extremities. In early cases of WDM, muscle biopsies were normal and neurophysiological examination revealed a myopathic pattern in half of the subjects. The strict distal distribution in manifest and heterozygous cases was confirmed in with magnetic resonance imaging, where also affection of posterior muscle groups of the lower extremity was demonstrated. Distinct clinical and histological features distinguishes WDM from Miyoshi myopathy and the distal myopathy described by Laing.