Atypical Familial Mediterranean Fever Presenting with Recurrent Upper Back Pain: A Case Report.

Familial Mediterranean fever (FMF) is a genetic autoinflammatory disease that is characterized by recurrent episodes of fever, serositis, and synovitis. FMF synovitis attacks resemble the clinical presentation of acute monoarthritis with pain and hydrarthrosis, which always resolve spontaneously. In most cases, colchicine will prevent these painful arthritis attacks in FMF. However, distinguishing these arthritis episodes from other febrile attacks with various clinical manifestations, including serositis, is important. We describe a Japanese patient with FMF who presented a febrile attack with severe abdominal and upper back pain (peri-scapula lesion), without any other joint involvement. A 44-year-old female patient presented with recurrent episodes of fever with abdominal and back pain. She carried heterozygous variants in exon 3 of the MEFV gene (P369S/R408Q). She was diagnosed with FMF according to Tel-Hashomer's diagnostic criteria for FMF. Colchicine treatment improved her febrile attcks with peritonitis, however, severe back pain was sustained. This unique aspect of severe pain attack was successfully resolved by canakinumab treatment, which is a specific interleukin-1β monoclonal antibody, and was finally diagnosed as FMF-related shoulder joint synovitis. Further investigations were needed to evaluate the effectiveness of interleukin-1 antagonists against colchicine-resistant arthritis in FMF patients.