[A patient with serious viral myositis following flu].

A 16-year-old girl presented at the emergency unit with myalgia following a flu-like episode. Laboratory tests indicated severe rhabdomyolysis and nephritis. Autoimmune-induced myositis was excluded on the basis of negative tests for antinuclear antibodies; prednisolone treatment was discontinued 1 week later. The patient recovered gradually and was discharged with physiotherapy 2 weeks later. High positive titres of complement-binding antibody against influenza B virus were found, i.e. 1:125 and 1:250 on days to and 25 of illness, respectively. Viral myositis is an uncommon disease entity that occurs following a viral infection, especially with influenza virus, that has been experienced for the first time. It usually runs a benign course: children often present with calf tenderness that resolves within a few days. There are cases, however, with a more serious course involving severe rhabdomyolysis and acute renal failure that can be sometimes fatal.