Periodic paralysis is a rare disease, characterized by transient weakness associated with abnormal levels of serum potassium. Muscle biopsy may show a wide range of abnormalities, vacuoles being more specifically linked to the disease. We analysed 17 muscle biopsies from 14 patients with periodic paralysis (14 hypokalemic, 2 hyperkalemic). All of them showed at least one histological abnormality. Fourteen specimens showed vacuoles that were peripheral, single, frequent and preferentially found in type I fibers. Frequency or severity of attacks did not correlate with the presence of vacuoles but those were more easily found in patients with long term disease. Ten biopsies showed tubular aggregates, specially on the patients with frequent crises or long term disease. A second biopsy was done in three patients and in two we observed a worsening of the histopathologic picture. One patient manifested interictal weakness with evident myopathic changes on the muscle biopsy. Nonspecific changes were found in variable degrees in 15 biopsies. Our study shows that vacuoles and tubular aggregates are frequent changes in periodic paralysis and therefore helpful for the diagnosis. Important myopathic findings in the muscle biopsy suggest a permanent myopathy which probably develops after severe crises or long term disease.
periodic paralysis; biopsy; skeletal muscle; vacuoles; tubular aggregates