Atypical Familial Mediterranean Fever Complicated with Gastrointestinal Amyloidosis Diagnosed due to Paroxysmal Arthralgia and Intractable Diarrhea, Successfully Treated with Tocilizumab

A 53-year-old man with recurrent episodes of large joint pain and a low-grade fever at irregular intervals for 16 years developed right knee and ankle arthralgia, watery diarrhea, and abdominal pain. Following an ileum and colon biopsy, he was diagnosed with gastrointestinal amyloidosis. We suspected familial Mediterranean fever (FMF) based on his history and administered colchicine; his symptoms subsequently improved. Thus, he was diagnosed with atypical FMF. After tocilizumab administration, the amyloid deposits disappeared. This case suggests that physicians should consider FMF even in cases with atypical symptoms in order to prevent the progression of amyloidosis and that amyloid deposits can be eliminated by interleukin (IL)-6 inhibition.