Protracted Febrile Myalgia Associated with Fever of Unknown Origin

Fever of unknown origin (FUO) is considered in children as fever >38.3°C (101°F) at least once a day for 8 days and more without any apparent diagnosis. There are lots of underlying factors for fever of unknown origin and the three most common etiologic categories in children are infectious diseases, connective tissue diseases, and neoplasms. In this article, we have presented a 15-year-old girl admitted with normal physical, and biochemical examination findings except fever and an elevated acute phase reactant. She was diagnosed with protracted febrile myalgia syndrome (PFMS) when severe myalgia was added to her complaints although she denied previously experienced periodic fever, abdominal pain, arthralgia or chest pain. We presented our case to emphasize that protracted febrile myalgia syndrome, one of the atypical clinical manifestations of Familial Mediterranean fever, may be the presenting symptom of Familial Mediterranean fever as well as an underlying cause of fever of unknown origin.