Diagnostic and Therapeutic Challenge of Metatarsalgia in a Patient With Rheumatoid Arthritis.

A 63-year-old female patient, with a past history of rheumatoid arthritis, presented with insidious pain on the left foot second and third metatarsophalangeal joints, associated with swelling and morning stiffness (mean time: four hours). Physical examination evidenced a tender and soft nodularity in the third intermetatarsal space, along with sharp pain, consistent with Morton's neuroma. Foot ultrasound suggested Morton's neuroma, but not excluding the possibility of rheumatoid arthritis involvement. Foot magnetic resonance imaging suggested the possibility of extensive synovitis of the third metatarsophalangeal joint, but not excluding the coexistence of Morton's neuroma because of the mass effect. Finally, the patient underwent an ultrasound-guided needle biopsy of the nodule, which confirmed metatarsophalangeal joint synovitis. The foot is a common location of rheumatoid arthritis manifestation, and metatarsophalangeal joint synovitis can mimic Morton's neuroma. After a definite diagnosis, the patient recovered lower limb functional impairment after introducing adalimumab and a rehabilitation program. This case highlights the importance of an accurate differential diagnosis, pharmacological rheumatoid arthritis control, and physical medicine and rehabilitation programs to optimal clinical and functional improvement.