High serum levels of creatine kinase: asymptomatic prelude to distal myopathy.

Two brothers and an unrelated man had serum creatine kinase values of 3000-8000 units when they were asymptomatic, and there was no weakness on examination. EMG and muscle biopsy showed changes indicative of myopathy. Years later, all three developed weakness that was limited to the gastrocnemius. Because siblings were affected, the disorder can be regarded as a form of muscular dystrophy. The distribution of weakness, serum enzyme changes, and histologic changes resembled an autosomal recessive distal myopathy first described by Miyoshi and differed from many other reported cases of distal myopathy. Our cases also indicate that myopathy may be asymptomatic.