Lyme Disease Presenting as a Spontaneous Knee Effusion.

Musculoskeletal complaints, which are frequently associated with Lyme disease, often prompt patients to see a physician. In particular, transient episodes of spontaneous knee effusion are common early in the progression of Lyme disease, and, if left untreated, 60% of patients diagnosed with the disease develop Lyme arthritis. This disease is easily treated with antibiotics; therefore, inclusion of Lyme disease in the differential diagnosis as a potential cause of a spontaneous knee effusion can prevent the development of more severe symptoms associated with the disease. However, the time required to receive test results and the inconsistencies between serum and synovial tests can complicate diagnosis of the disease.