[McArdle's disease in a 14-year-old girl with fatigability and raised muscle enzymes].

INTRODUCTION: McArdle's disease is a disorder of muscle energy metabolism caused by a deficit of muscle phosphorylase. The typical form presents with fatigability muscle cramps and pains triggered by physical exercise. Some cases have few symptoms. We report the case of a 14 year old girl diagnosed on finding a significantly raised CPK, studied following her complaint of fatigability. CLINICAL CASE: A 14 year old girl presented with a CPK of 1,243 UI/l (normal 10-32) which had been requested in view of her fatigability. She had never had cramps, muscle pains or dark urine. Neurological examination was normal. The levels of CPK after intense exercise on the previous days were 7,459 UI/l, and after rest for one week were 283 UI/l (normal 25-230). The ischemic exercise test showed that she was unable to finish the test, with flat lactate and pyruvate curves and markedly raised ammonia (basal 89 and maximum 571 micrograms/dl). On muscle biopsy, the morphology of the striated muscle was seen to be normal and staining for myophosphorylase was negative. CONCLUSIONS: The fluctuations of muscle enzyme levels in relation to exercise orientate the diagnosis towards a disorder of muscle energy metabolism. To detect this, the investigation should be carried out following severe exercise for several days and then compared with a further test after some days of rest. The ischemic exercise test permits identification of defects of glycogenolysis, orientating the choice of suitable histochemical, enzymatic or molecular biological tests.