Benign Acute Childhood Myositis During Influenza B Outbreak

Benign acute childhood myositis (BACM) is a syndrome classically occurring in children during the convalescent phase from a febrile upper respiratory tract infection, most commonly after influenza B. BACM can cause difficulty walking due to severe calf pain. Laboratory results show increased serum creatinine kinase and AST. Although alarming, BACM is self-limiting with symptoms disappearing within a week. Herein, we described a case series of BCAM in children in two cities in Poland during the influenza outbreaks in 2012/2013 and 2014/2015. We discussed the presentation and the clinical workup and examinations of the myositic syndrome. In addition, we evaluated the association of BACM with influenza B. We detected specific IgG against influenza B virus in 83% of the children diagnosed with BCAM. Reports from the National Institute of Public Health - National Institute of Hygiene in Warsaw, Poland confirmed a high rate of influenza B cases during both epidemic seasons in question.