Myopathic causes of exercise intolerance with rhabdomyolysis

We review the muscular dystrophies and metabolic myopathies associated with myalgia and rhabdomyolysis together with some less well‐recognized associations based upon the personal practice of the authors. A careful history and clinical examination will direct investigation towards an accurate molecular diagnosis. Non‐specific exercise‐induced myalgia in the presence of muscle hypertrophy and a high creatine kinase will point towards a muscular dystrophy. Symptoms occurring within minutes of exercise and with isometric contraction, especially with a history of a ‘second wind’ phenomenon, suggest a disorder of glycogen metabolism. In those patients in whom symptoms occur after prolonged exercise, infections, fasting, stress, and cold, a disorder of fatty acid oxidation should be considered. Heat‐induced rhabdomyolysis caused by exercising in hot and humid climates should lead the clinician to suspect a mutation in RYR1 . Serum creatine kinase level should be a checked in all children presenting with leg pains. A careful history and examination and laboratory confirmation of myoglobinuria will target investigations leading to a correct molecular diagnosis.