Abstract
An electron microscopic study of the flexor carpi radialis muscle from 2 patients with MeArdleʼs disease is presented. Glycogen accumulation occurred primarily in the intermyofibrillar space of the I band and under the sarcolemma. Increased amounts of glycogen were also noted between the thin filaments within the I band and. occasionally, between filaments in the A band.The most significant alteration in the muscle fiber, in terms of muscle fiber function, was disorganization of the myofibrils at the level of the I band. This was due to compression of the myofibrils by excess glycogen in the inter-myofibrillar space and displacement or replacement of thin filaments within the myofibrils by glycogen deposits.It is suggested that these alterations in myofibril structure, due to glycogen deposition, may lie one of the causes of the permanent weakness that has been observed in the later stages of McArdleʼs disease.The distribution of excels glycogen in McArdleʼs disease may provide indirect evidence for tile localization of skeletal muscle phosphorylase.Electron microscopic study of phosphorylase deficient muscle in physiological contracture, removed 30 minutes after the onset of ischemic exercise, revealed mitochondrial alterations and dilatation of portions of the sarco-plasmic reticulum.