[Acute myositis associated with influenza].

Benign acute myositis associated with influenza is reported from all over the world. The characteristics of this disorder is calf pain and difficulty walking during a viral illness (3-8 days) and creatine kinase levels are mildly or moderately elevated. Recovery occurred within 1 week. Midchildhood (mean age: 6-8 years) is most commonly affected and boys are more commonly than girls and its ratio is 2.4 : 1 by Shimizu in Japan (1993). Elderly patients are also reported. Viral studies show that influenza B is more commonly than influenza A and the ratio is 6 : 1 by Hu in Taiwan (2004), 2.4 : 1 by Shimizu in Japan (1993). Muscle histology revealed isolated segmental muscle degeneration and necrosis without frank myositis. A direct role of influenza virus in its genesis is not clear. An age-related response and occurrence primarily on boys may reflect a genetic predisposition.