Asymptomatic McArdle's disease associated with hyper-creatine kinase-emia and absence of myophosphorylase

Asymptomatic elevations of serum creatine kinase (CK) may be observed in patients undergoing routine health assessment or evaluation for an acute illness. Diverse myopathic conditions may cause asymptomatic hyper-CK-emia, including polymyositis, congenital myopathies, and mitochondrial myopathies.1 Elevations of CK are common in patients with myophosphorylase deficiency (McArdle's disease) not only during episodes of exertional myalgia and cramps, but also during rest.2 We report an asymptomatic patient with negligible muscle glycogen phosphorylase (MGP) activity and marked elevation of CK. Genetic analyses showed that the patient is heterozygous for an uncommon mutation at codon 396 of the MGP gene; the genetic defect affecting the other allele remains undetermined. Case report. A 15½-year-old girl who had extensively participated in competitive athletics and aerobics without neuro-muscular symptoms experienced an acute episode of gastrointestinal discomfort, emesis, and dehydration, unassociated with muscle cramps, myalgia, or pigmenturia, which resolved quickly with the administration of IV fluids. Abnormal laboratory studies included a serum CK of 11,649 U/L, which remained elevated for 14 days with a maximum of 41,000 U/L. Before neurologic evaluation, she refrained from athletic activities for 1 month. Results of her neurologic and general physical examinations were normal, but serum …