Case Diagnosis: Lyme Arthritis

Case Description: Patient 1 is a 26 year old male who presented in March with severe right knee pain and swelling for two weeks. He had a similar episode a month prior, but it resolved. The second episode progressed with pain from knee to foot and numbness on top of the foot. He had no known history of tick bites, travel, or trauma, but endorsed contact with a dog. On physical exam, he had a right knee effusion with limited ROM, diffuse joint line tenderness, positive McMurray’s, and pain with ligamentous testing. Synovial fluid of the joint showed WBC count 44,467 and was positive for Lyme. He was treated with doxycycline. MRI findings were limited to ACL laxity and inflammation.

Patient 2 is a 24 year old male who presented in December with progressive right knee and calf pain for one week. He had been fishing in the woods a few weeks prior with no trauma. Joint aspiration showed a positive Lyme PCR and WBC count 37,520, and he was treated with doxycycline. Aspiration was repeated for recurrent effusion, and an MRI was done due to persistent pain. MRI showed bone contusion, ACL laxity, and inflammation.

Discussions: Lyme disease is transmitted by Ixodes scapularis ticks, which appear in late spring and early summer; however,Lyme arthritis may occur during any season. Ticks infected with the spirochete B. burgdorferi are primarily found in the Northeastern and upper Midwestern US. B. burgdorferi strains of Lyme often disseminate to joints, tendons, or bursae early in infection.Lyme arthritis presents later, with an adaptive immune response that results in spirochetal killing.

Conclusions: Lyme arthritis can present at any time of year, and clinical suspicion in endemic regions should remain high even without a known history of tick exposure or erythema migrans rash.