McArdle Disease

McArdle disease, or glycogen storage disease type V, is an autosomal recessive disorder caused by myophosphorylase deficiency. Clinical features include exercise-induced muscle cramps, fatigue, myoglobinuria, and second-wind phenomenon. Pathophysiology involves impaired glycogenolysis in skeletal muscle, leading to energy deficits during exertion. Diagnosis is based on clinical history, elevated CK, genetic testing, and muscle biopsy. Management includes tailored exercise programs, carbohydrate supplementation, and avoidance of strenuous activity; prognosis is generally good with lifestyle adaptation.