(Kiosk 2) Bilateral Knee Effusions as an Uncommon Presentation of Reactive Arthritis

Case Diagnosis: Bilateral Knee Pain and Effusions Secondary to Reactive Arthritis

Case Description or Program Description: A previously healthy 37-year-old female presented with 6 weeks of bilateral, non-radiating knee pain and swelling. Endorsed fatigue, morning stiffness, and jaw pain. Had viral respiratory illness 2 months prior. No trauma or prior knee injuries. No history of rheumatological conditions, but sister recently diagnosed with rheumatoid arthritis. Knee exam showed bilateral effusions and tenderness. No warmth or erythema. Range of motion limited. Sensation and strength preserved.

Setting: Outpatient physiatry clinic

Assessment/Results: No osseous abnormalities on knee radiographs. Bilateral ultrasound demonstrated suprapatellar recess effusions with complex fluid and significant synovial hypertrophy. Ultrasound-guided knee arthrocentesis and fluid analysis notable for WBC of 13,000 and 3,000 of right and left knee, respectively. No crystals or bacteria seen. Rheumatological studies: negative rheumatoid factor, negative CCP, positive HLA-B27, weakly positive ANA titer, mild ESR/CRP elevations. Patient seen by Rheumatology and diagnosed with HLA-B27 positive spondyloarthritis, reactive vs. psoriatic. She was started on a prednisone taper, methotrexate, tizanidine, and meloxicam.

Discussion (relevance): Bilateral knee pain and effusions in a young, otherwise-healthy patient necessitates a broad differential diagnosis, including infectious, inflammatory, and auto-immune causes. In this case, reactive arthritis was most likely given the synovial fluid analysis and patient’s recent viral illness and lack of psoriatic signs. Bilateral knee effusions are an uncommon presentation of reactive arthritis, which is typically asymmetrical. Ultrasound is a quick and inexpensive way to evaluate for a complex joint effusion and synovial hypertrophy as seen in reactive arthritis, and can assist with knee arthrocentesis and synovial fluid analysis for confirmatory diagnosis.

Conclusions: Reactive arthritis can present as bilateral knee pain and effusions. Ultrasound is an effective tool to confirm the diagnosis of reactive arthritis.