Unilateral knee effusion in an elderly patient: an unusual presentation of rheumatoid arthritis.

Unilateral atraumatic knee effusion is a relatively common presenting complaint among geriatric patients in primary care and musculoskeletal speciality clinics. Gout, pseudogout, degenerative joint diseases and reactive arthritis are the most common causes of the atraumatic knee effusions. Rheumatoid arthritis very rarely presents as arthritis of one or two large joints. Arthrocentesis, plain radiography and screening blood tests should be performed to help narrow the differential diagnosis. In some cases, advanced imaging modalities such as MRI may be indicated. This study reports a case of rheumatoid arthritis in a 75-year-old gentleman with oligoarthropathy of two large joints as the presenting symptoms.