Introduction: McArdle disease is a glycogenosis (type V) due to an inherited myophosphorylase, deficit manifested by exercise intolerance and occasionally by rhabdomyolysis. In about 2/3,  diagnosis is made in the adult age, with a prior long-lasting symptomatology. Due to low suspicion level and presence of mild symptoms in several cases, the prevalence of this disease is probably underestimated.

Clinical reports: Case 1: 10-year-old girl complaining from an early age of aching limbs, cramps and weakness after exercise, sometimes associated with increased heart rate and thoracic pain. Complaints were more frequent during the first minutes of exercising. She had one previous episode of dark urine which resolved spontaneously. Family history was unremarkable. Physical examination was normal. Laboratory results revealed elevated serum level of total creatine kinase (hyperCKaemia). The 'classic' forearm test revealed no increase in lactate levels and molecular studies confirmed the diagnosis. Case 2: 15-year-old male referred to the paediatric neurology clinic for persistent hyperCKaemia. He had no complaints of fatigue or exercise intolerance. Physical examination revealed mild weakness mostly in proximal limb muscles, with no other abnormalities. Muscle biopsy was suggestive of metabolic myopathy and molecular studies confirmed the diagnosis.

Comments/Discussion: As clinical manifestations can be subtle and non-specific, McArdle disease should be considered in every child with fatigue and exercise intolerance coupled with hyperCKemia. A regular low-moderate aerobic exercise and pre-exercise carbohydrates can ameliorate the clinical manifestations. We would like to emphasize the importance of an early diagnosis to prevent progressive muscle weakness and renal complications.