Rheumatoid nodule presenting as an indeterminate soft tissue mass in the sole of the foot

A 64-year-old lady with a background of rheumatoid arthritis presented to the foot and ankle clinic with lump underneath the sole of her foot causing significant discomfort. Examination revealed she had a swelling of the first and the second metatarsophalangeal joints. Magnetic resonance imaging revealed abnormal soft tissue thickening between the second and the third metatarsal and a single large encapsulating indeterminate soft tissue mass with a peripheral inflammatory rim. The appearance was suggestive of a malignant sarcoma rather than a rheumatoid nodule or rheumatoid tenosynovitis. The patient was referred to the regional sarcoma unit where the scans were reviewed, and a sarcoma was ruled out. The patient then underwent excision of the indeterminate soft tissue mass. Histology revealed granulomatous infiltration suggestive of a rheumatoid nodule. This has not been described previously in the literature.