An atypical “arthritis” in a patient with rheumatoid arthritis

A 42-year-old woman presented inflammatory monoarticulararthritis of the proximal interphalangeal joint of the left ring fin-ger with a previous history of rheumatoid arthritis well controlledby abatacept. This mono-arthritis was resistant to non-steroidalanti-inflammatory drugs.Biologicalevaluationswerenormal.Plainradiograph (Fig. 1A), completed by transverse CT scan (Fig. 1B) andcoronal T2-weighted fat-suppressed magnetic resonance imag-ing (Fig. 1C) showed a small, radiolucent, eccentric lesion withinternal ossification on the radial side of the second phalanx ofthe 4th finger with cortex thickening (arrow), edema within andaround the bone but without periosteal bone formation and prox-imal interphalangeal joint involvement with erosion (arrowhead).Histopathological examination confirmed the diagnosis of osteoidosteoma. CT-guided percutaneous radiofrequency thermal abla-tion was refused by the patient, who preferred to wait given the