Myopathic evolution of an exertional muscle pain syndrome with phosphorylase b kinase deficiency

The symptoms of a myopathy permanently affecting limb girdle muscles are reported in a 31-year-old woman who has been presenting an exertional muscle pain syndrome with myoglobinuria for 20 years. Investigations revealed a slightly decreased utilization of glycogen in muscle, while its storage affected only rare type 2 fibers. Active phosphorylase was undetectable and phosphorylase b kinase activity was clearly decreased in muscle cells, but normal in erythocytes, lymphocytes and cultured fibroblasts.