Peripheral nerve and vasculature involvement in myophosphorylase deficiency (McArdle's disease)

A 60 year old white male presented with atypical chest pain and exercise-induced myalgia. Physical examination revealed slight proximal limb muscle weakness and wasting. Serum creatine phosphokinase levels were persistently elevated and electromyography showed changes consistent with a mild myopathy. Light microscopic and ultrastructural study revealed excess free glycogen within skeletal muscle, and histochemical staining showed absence of myophosphorylase activity. Biochemical quantitation confirmed the diagnosis of McArdle's disease by demonstrating absent phosphorylase activity in skeletal muscle with increased glycogen. In addition, increased amounts of free and membrane-bound glycogen were found within axons, Schwann cells, fibroblasts and occasional vascular smooth muscle and endothelial cells that had been included within the skeletal muscle biopsy. This case demonstrates more widespread glycogen accumulation than has been previously reported in McArdle's disease.