According to research published in The Journal of the American Academy of Orthopaedic Surgeons, spontaneous knee effusion can be a primary symptom of Lyme disease even without the presence of a “bull’s eye” rash. 

A literature review conducted by researchers from Harvard Medical School, found that early diagnosis and antibiotic therapy can prevent the development of more severe symptoms of Lyme disease. If symptoms have been present for <14 days, the Lyme disease test may need to be repeated as the test can be negative for the first two weeks of an infection, explained Elizabeth Matzkin, MD, the study’s lead author. 

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Currently, a two-tier blood test is the standard care for diagnosing Lyme disease. Treatment with antibiotics is successful in 99% of patients who are diagnosed early, and in 90% of patients who are diagnosed later. Over half of the patients left untreated can develop Lyme arthritis with an increased risk of permanent joint damage. 

Knee effusions caused by Lyme disease are often “very large, not activity-related, and mostly pain-free,” compared to septic or arthritic knees that present with significant pain, explained Dr. Matzkin. Clinicians should always consider whether a spontaneous knee effusion might be caused by Lyme disease and test as needed in areas where Lyme disease is common. In areas where Lyme disease is not prevalent, the clinician should ask if the patient has traveled to such an area prior to diagnosis.

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