Late-onset distal muscular dystrophy affecting the posterior calves.

Miyoshi myopathy, caused by mutations in the membrane protein dysferlin, is the most common muscular dystrophy that presents in the posterior calves. Its onset is before the age of 30 years and it is associated with marked elevations of serum creatine kinase (CK). In contrast, little is known about calf myopathies with onset after the age of 30, and it is not clear whether such patients have a dysferlinopathy. We describe five patients with a myopathy predominantly affecting the calf muscles, with onset after the age of 30. Muscle tissue was analyzed by immunoblot for dystrophin and dysferlin. All five had normal dysferlin but one had a dystrophinopathy. Serum CK levels ranged from 3 to 15 times the upper limit of normal. In contrast, all of 13 patients presenting before age 30 with calf weakness had a dysferlinopathy. Thus, isolated calf atrophy and weakness with onset after age 30, and associated with serum CK levels that are only moderately elevated, represents a distinct myopathy phenotype. Most of these cases are sporadic, although the overall phenotype appears genetically heterogeneous and dysferlinopathy is uncommon.