Clinical spectrum of McArdle disease: three cases with unusual expression

Three cases of myophosphorylase deficiency with unusual clinical expression are presented. The 1st had clinical characteristics suggesting a mild congenital myopathy, and the patient never experienced cramps or myalgias. The 2nd had a slowly progressive myopathy without cramps or myoglobinuria which was detected by chance. The 3rd presented with myoglobinuria and acute renal failure, unrelated to a triggering effort, and with permanent weakness and wasting. In all cases, muscle biopsy demonstrated a vacuolar myopathy with free glycogen increase and absence of myophosphorylase activity, confirmed by biochemical assays. The cases confirm the wide clinical spectrum of McArdle disease.