Rheumatoid Arthritis Masquerading as Fibromyalgia

Symptoms of inflammatory arthritis such as rheumatoid arthritis (RA) can overlap with fibromyalgia syndrome (FMS). Moreover, FMS and RAcan coexist. Hence, the diagnosis of low intensity, antibody-negative RAmay present a challenge. Here, we present the case of a middle-aged woman thought to have FMS, osteoarthritis and osteoporosis for 4 years prior to being diagnosed as seronegative RAon musculoskeletal ultrasound (MSKUS). Targeted therapy with etanercept led to a complete clinical response and normalization of previously elevated C-reactive protein. We conclude that MSKUS is a sensitive tool for distinguishing low-intensity inflammatory arthritis from FMS with important clinical consequences.