MYOSITIS ASSOCIATED WITH INFLUENZA B INFECTIONS

An epidemic of acute myositis affecting children occurred in Seattle during March-May, 1973, with most pediatricians seeing several cases. The disease was characterized by a prodrome of upper respiratory symptoms, fever, and headache, followed in several days by sudden onset of refusal to walk or abnormal gait with toe-walking. Gastrocnemius-soleus muscles were chiefly affected, being tender, swollen and painful. Muscle symptoms, although dramatic, resolved completely within 3-7 days without special therapy. Transient elevations of serum CPK or SCOT were noted in 16 of 17 patients tested. Influenza B virus was isolated from throat swabs of 11 of the 17 patients studied. One of the isolates was characterized, and was antigenically “intermediate” between the 1967-71 isolates and B/Hong Kong/5/72. Paired sera from 12 patients were tested for HI antibodies to strain B/Hawaii/3/73 (an “intermediate”); (4 patients had a greater than 4-fold titer rise, and 4 had detectable but lesser titer rises. No titer rises by CF testing were detected for 8 other respiratory agents. This unusual complication of influenza has been previously reported in Stockholm (1955), Toronto (1969-70) and Boston (1972). The distinctive clinical picture of dramatic but self-limited calf muscle myositis following a flu-like illness makes this a clearly recognizable syndrome which should not be confused with dermatomyositis.