The patient is a 57 year-old woman with a 10 year history of morning stiffness, bilateral wrist swelling, and fatigue. She was diagnosed with seronegative RA based on her symptoms, and was treated with NSAIDs and Plaquenil. She developed some mild right hip pain 1 month ago, and presented to clinic for consultation. On exam, there was mild pain and limitation of motion in the right hip. Radiographs were obtained.
Plain films of the hip demonstrate a large periarticular intraosseous cyst and/or erosion.(Film 1) There is mild global joint space narrowing as well. The CT scan confirms the presence of a large cyst with smaller erosions of the intracapsular portion of the femoral neck.(Film 2)
Correct Diagnosis: Cystic Rheumatoid Arthritis
Approximately 10% of patients with rheumatoid arthritis have the cystic form. Cystic RA is characterized by the presence of symmetric periarticular intraosseous cysts without conspicuous erosions, and is generally felt to have a more benign course than classic RA. Cysts are also seen in patients with rheumatoid nodulosis (RN), a rare condition characterized by rheumatoid nodules, rheumatoid factor positivity, and intermittent arthritis.
- Lycklamaa Nijeholt G, Gubler FM, Scholten RJ, Dinant HJ. Comparison of cystic rheumatoid arthritis and erosive rheumatoid arthritis. J Rheumatol 23(3):447-52, 1996.
- Gubler FM, Maas M, Dijkstra PF, de Jongh HR. Cystic rheumatoid arthritis: description of a nonerosive form. Radiology 177(3):829-34, 1990.