McArdle's disease is a hereditary deficiency of myophosphorylase, the enzyme that converts glycogen to glucose-1-phosphate.
Onset is usually in the pediatric age group, but a late onset in adulthood may also occur.
Clinical features:
(1) exercise intolerance
(2) myalgias and muscle cramps
(3) asymmetric proximal muscle weakness
(4) recurrent episodes of rhabdomyolysis
(5) repeated episodes of acute renal failure
Laboratory findings:
(1) elevated serum creatine kinase and myoglobinuria during rhabdomyolysis
(2) absence of a rise in serum lactate after ischemic exercise testing of the forearm.
A skeletal muscle biopsy will show a vacuolar myopathy. Enzymatic staining shows an absence of myophosphorylase activity.
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Specialty: Surgery, orthopedic
ICD-10: ,