McArdle's disease with late-onset symptoms is an unusual cause for muscle disease in older patients. The case of a patient with McArdle's disease whose symptoms began at 60 years of age is presented, and seven previous cases of late-onset McArdle's disease reported since 1963 are discussed. In five of the eight patients, the clinical presentation was similar to the early onset disorder with exercise intolerance, cramps, and myoglobinuria. In contrast, the remaining three patients presented with fixed proximal limb and bulbar weakness. Electromyography confirmed a myopathic process in four of four patients. Results of the forearm ischaemic exercise test were positive in seven of seven patients with complete myophosphorylase deficiency; results of muscle biopsies were diagnostic in all patients. McArdle's disease with late-onset symptoms is rare and clinically more variable than the early onset disorder.
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