Benigne Myositis nach Influenzainfektion

The clinical course of a 5.5-year-old boy is presented; he suddenly complained of severe calf pain 11 days after the start of an airway infection accompanied by cough, cold, and fever. Due to the pain, he was no longer able to walk. Furthermore, the boy exhibited fever around 39°C despite the continuous administration of antipyretic drugs and antibiotics. Comprehensive diagnostics were performed (laboratory analyses, magnetic resonance imaging of the skeletal muscle, bone marrow puncture, x-ray, autoimmunological analyses, exclusion of muscle dystrophy, ultrasonic surveys, search for pathogenic agents via serology and nasopharyngeal secretions, electrocardiography, echocardiography, metabolic analyses). Finally, based on all clinical findings and laboratory results, the patient was diagnosed with benign acute childhood myositis. A connection with a previous influenza infection was likely, based on relevant laboratory findings (leucopenia, no increase in C-reactive protein, no evidence for further inflammation mediators) and positive influenza serology. The patient recovered completely despite the prolonged process. A new aspect of this form of myositis, first described in 1957 by Lundberg, was established in the form of a clearly increased number of circulating immune complexes with complementary factors C3 and C1. To the author’s knowledge, this has not been previously described.