[Miyoshi distal myopathy: specific signs and incidence]

We report 21 French patients (12 males and 9 females), presenting a distal myopathy of Miyoshi type. The main clinical features of these patients were 1) onset in late adolescence or early adulthood (mean age: 20.3 years), 2) early and predominant involvement of the posterior compartment muscles of legs, 3) marked elevation of serum CK (from 10 to 50 times the normal value), 4) dystrophic features with a necrotic regeneration pattern without vacuole in muscle biopsy. All cases were sporadic and a consanguinity of parents was found in five cases. The clinical course was relatively mild: twelve patients could walk without aid; However four patients were severely disabled. Four patients were initially considered as having polymyositis; corticosteroids and immunosuppressive drugs were always inefficient. A genetic linkage to chromosome 2 was ascertained in five cases. In our experience the Miyoshi distal myopathy is the most common form of distal myopathy, particularly in young patients.