Protracted febrile myalgia syndrome as the first manifestation of familial Mediterranean fever in children: case-based review

Protracted febrile myalgia syndrome (PFMS) is one of the rare conditions characterized by long standing severe myalgia and fever in familial Mediterranean fever (FMF) patients. Laboratory studies show elevated values of inflammatory markers and normal creatinine phosphokinase (CPK) levels. Rarely, PFMS may be the first manifestation of FMF and this makes the diagnosis of FMF and PFMS challenging. The aim of this report was to describe case series of PFMS patients without previous diagnosis of FMF and discuss with other pediatric PFMS cases described in the literature. Six patients with PFMS as the first manifestation of FMF from two Pediatric Rheumatology clinics were presented. The male: female ratio was 1:1. The median (min-max) age at diagnosis was 7.05 (5.5-15.5) years. All patients had severe myalgia. No fever was detected in two patients. Only one patient had rash. Markedly elevated acute phase reactants were observed in all patients. CPK levels were normal in all patients. Also, we searched the PubMed/MEDLINE, Google Scholar, Web of Science and Scopus databases from inception to May 2020, using the keywords 'familial Mediterranean fever, protracted febrile myalgia, child' and 52 pediatric PFMS were found. In the literature, three patients did not have fever, and nineteen patients were not previously diagnosed with FMF as our patients. As a conclusion, PFMS may be the first manifestation of FMF. It should be suspected in cases with prolonged severe myalgia with or without fever, and high acute phase reactants.