Acute myositis associated with influenza B infection.

An epidemic of acute myositis affecting children occurred in association with influenza B infections. The myositis followed the initial influenza-like episode, and almost exclusively involved the gastrocnemius and soleus muscles. Patients improved without specific treatment and made a complete recovery in four to five days. Laboratory studies characteristically showed elevated CPK, SGOT values, and a low peripheral white blood cell count. Influenza B virus was isolated from 11 of the 17 patients studied. This influenza-associated acute myositis of childhood is a recognized syndrome that should not be confused with dermatomyositis.