Abstract
Synovial chondromatosis (SC) is an infrequent condition characterized by cartilaginous metaplasia of synovial articular membrane, tendinous sheaths and bursae. Hyaline cartilage nodules progressively calcify and eventually detach from synovial tissue, forming intra-articular bodies.
SC is classified in primary and secondary. Primary SC is idiopathic and its prevalence is not well established. It is thought to have a higher recurrence rate than secondary SC, which in turn, occurs after trauma, infection, local pre-existing condition or systemic disease. Secondary SC appears to have better results with surgical intervention. It may affect any synovial joint, generally depicting a monoarticular and unilateral distribution.
A 6-year-old female with juvenile psoriatic arthritis (onset 4 years) was successfully treated with sulfasalazine. She presented with de novo right knee pain and claudication, associated with effusion and loss of range of motion, which responded partially to non-steroid anti-inflammatory drugs. Laboratory tests were unremarkable, showing mildly increased erythrocyte sedimentation rate.
Over the next few weeks, elbow synovitis, dactylitis and tarsitis appeared, and the patient was switched to methotrexate and received a knee steroid intra-articular injection. Synovial fluid had inflammatory characteristics and was sterile.
All manifestations improved, except for the knee. MRI revealed findings consistent with synovial chondromatosis. The patient underwent arthroscopic debridement with partial synovectomy. Histopathology findings were compatible. The patient improved steadily and remains in clinical remission at 1.5 years of follow-up.
The authors describe an atypical presentation of synovial chondromatosis, given the occurrence in a female child. Despite its typical articular localization, the age of onset and unspecific symptoms, along with the existence of a previous rheumatologic condition, hindered the diagnosis.

Key words: Synovial chondromatosis, knee arthritis