[Muscle carnitine deficiency associated with myalgia and rhabdomyolysis following exercise]

A case of 16-year-old female with myalgia and myoglobinuria following prolonged exercise was reported. Neurological examination revealed mild weakness of proximal muscle in the lower extremities. Serum CK, LDH, myoglobin were significantly increased during the attacks. On biopsy, the muscle fibers contained myriad lipid-filled vacuoles, in predominantly type 1 fibers. Electron microscope examinations revealed numerous lipid droplets adjacent to mitochondria and glycogen particles. Carnitine level in the patient's muscle was markedly reduced (under 5% of control), but the serum carnitine concentration was normal. The muscle carnitine palmityl transferase level was not depressed. A forearm ischemic test resulted in normal lactate production. On exercise tolerance test by a bicycle ergometer, mild exercise (15-30 watts for 15 minutes) induced myalgia and marked elevation in serum CK, lactate and pyruvate, while severe exercise showed no increase in serum CK level. The findings suggest that the energy production system in the skeletal muscle was impaired. However, the enzyme activities of NADH oxidation in mitochondria and the anaerobic glycolysis pathway were within normal limits. During fasting (36 hours), there was a normal production of ketone bodies, suggesting that hepatic metabolism of lipids was normal. She showed good response to L-carnitine therapy.