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June 1969

Myopathy of Hypokalemic Periodic Paralysis: An Electron Microscopic Study

Author Affiliations

From the Division of Neuropathology, departments of pathology (Drs. Macdonald and Rewcastle) and medicine (Dr. Humphrey), University of Toronto and the Toronto General Hospital.

Arch Neurol. 1969;20(6):565-585. doi:10.1001/archneur.1969.00480120011001

EREDITARY intermittent flaccid paralysis of skeletal muscle is at present classified into three types on the basis of the changes in the serum potassium during the paralytic attack. The hypokalemic form was the first to be clinically recognized, and is the most common of the three variants, more than 600 cases having been described in the literature by 1959.1 The clinical manifestations of this disease will not be detailed here as many reviews are available.2-5 Worthy of emphasis, however, is that permanent proximal muscle weakness may occur. This feature was first noted by Oppenheim6 in 1891 and was later thought to be a variant of spinal muscular atrophy occurring in conjunction with periodic paralysis.7 However, it has now become apparent that permanent myopathic weakness is not uncommon, and not dependent upon severe or repeated paralytic attacks.8-10

The histological appearance of the skeletal muscle in such

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