Which histologic findings are characteristic of periodic paralyses (PP)?

Updated: Apr 30, 2018
  • Author: Naganand Sripathi, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Muscle biopsy is abnormal, more typically in patients with hypokalemic periodic paralysis (PP) than in patients with hyperkalemic periodic paralysis (PP). Histologic findings in hypokalemic PP include the following:

  • The most characteristic abnormality is the presence of vacuoles in the muscle fibers. Sometimes, they fill the muscle fibers, and in some patients, groups of vacuoles may be noted. These changes are more marked in hypokalemic PP than in hyperkalemic PP. In the latter, the vacuoles are small and peripherally located. Reports of muscle biopsy findings in PC are few and the vacuolar changes are less frequent.

  • Signs of myopathy include muscle fiber size variability, split fibers, and internal nuclei. Muscle fiber atrophy may be present in clinically affected muscles.

  • Tubular aggregates may be seen in some patients. Tubular aggregates are seen in type II fibers. They are subsarcolemmal in location. This abnormality is seen only in hypokalemic PP.

  • Muscle fiber necrosis is rare.

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