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September 1968

The Myopathy of Hyperkalemic Periodic Paralysis: An Electron Microscopic Study

Author Affiliations

From the Division of Neuropathology, Department of Pathology (Drs. Macdonald and Rewcastle), and the Department of Medicine (Dr. Humphrey), University of Toronto and the Toronto General Hospital.

Arch Neurol. 1968;19(3):274-283. doi:10.1001/archneur.1968.00480030052005

HYPERKALEMIC periodic paralysis has been recognized as a distinct disorder only since 1951 when several generations of a family were described suffering from episodes of periodic paralysis without an accompanying fall in the serum potassium.1 Gamstorp further elucidated the main clinical features of the disease and established that the serum potassium was elevated during the paralytic attack.2,3 Later reports emphasized the common occurrence of myotonic features4,5 and that permanent myopathic weakness involving the abdominal and proximal limb girdle muscles may occur.6,7 Early muscle biopsies failed to reveal significant histopathological alterations.8,9 However, more recent reports have demonstrated infrequent central vacuolation of minor proportions with some nonspecific myopathic features7,10; these changes are similar to, but less marked, than those in hypokalemic periodic paralysis. Publications on the fine structure of skeletal muscle in this condition have shown few abnormalities11 or vacuoles possibly arising from the

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