[Arthritis revealing an osteoid osteoma in a patient with spondylarthropathy].

Intra-articular osteoid osteoma is rare and difficult to diagnose. We report a 38-year-old woman who presented with an inflammatory monoarticular arthritis in the right ankle in the context of a spondylarthropathy, otherwise well-controlled by leflunomide. This monoarthritis was resistant to all types of treatment. Investigations led to the diagnosis of an intra-articular osteoid osteoma. This original observation is the first description of an osteoid osteoma developing in a patient already known to have inflammatory rheumatism. All previous reported cases were monoarthritis consecutive to the osteoid osteoma itself and interpreted as incipient inflammatory rheumatism.