Familial Mediterranean fever mimicking septic arthritis.

We report the case of a young Lebanese female who presented with recurrent episodes of left knee and calf swelling and a synovial fluid leucocyte count suggestive of septic arthritis, however bacteriologic cultures were negative. Familial Mediterranean fever (FMF) was suspected in view of a positive family history and genetic analysis for the mutations in the pyrin/marenostrin (MEFV) gene revealing a homozygote mutation at methionine-694-valine. The arthritis was controlled with prophylactic colchicine therapy. FMF should be considered in the differential diagnosis of acute monoarticular arthritis with elevated synovial fluid white blood cells counts in regions with high incidence of FMF.