'Water on the knee' could be early sign of Lyme disease

November 1, 2015, American Academy of Orthopaedic Surgeons

Spontaneous knee effusion, also known as "water on the knee," can be a primary symptom of Lyme disease, even when patients do not exhibit a "bull's eye" rash, another common Lyme disease symptom. According to a literature review appearing in the November issue of The Journal of the American Academy of Orthopaedic Surgeons (JAAOS), early diagnosis and antibiotic treatment can prevent the development of Lyme disease's more severe symptoms.

Lyme borreliosis, or Lyme disease—the most common vector-borne illness transmitted by insects—is prevalent in the Northeast and upper Midwest regions of the United States. Over 30,000 cases are reported to the Centers for Disease Control and Prevention (CDC) each year and likely over 300,000 new cases occur but go unreported.

"It is important to catch and treat Lyme disease early because the symptoms get progressively worse over time," said Elizabeth Matzkin, MD, lead study author and assistant professor of orthopaedic surgery at Harvard Medical School. "However, the lab tests used to diagnose Lyme disease can take time to process, and there are certain circumstances in which immediate may be recommended before the lab results are complete." If symptoms have been present for less than two weeks, the Lyme test may need to be repeated as the test can remain negative the first two weeks of an infection.

The current standard of care for the diagnosis of Lyme disease is a two-tier blood test. Antibiotic treatments are successful in 99 percent of patients who are diagnosed early and in 90 percent of patients who are diagnosed later. If left untreated, 60 percent of patients eventually develop Lyme arthritis, with the most severe cases having higher risks of permanent joint damage.

"Half of patients do not recall a tick bite or observe a rash, and early symptoms are not always detected when a physician diagnoses a knee effusion," said Dr. Matzkin. "One of the most notable differentiating factors is, while septic or arthritic knees usually come with significant pain, knee effusions caused by Lyme disease are often very large, not activity-related, and mostly pain-free."

Early symptoms of Lyme disease, which include fatigue, chills, fever, headache, muscle and joint aches, and swollen lymph nodes, occur three to 30 days after exposure and are not always present.

In areas where Lyme disease is common, physicians should always consider whether a spontaneous knee effusion might be caused by the and test accordingly. In areas of low prevalence, the clinician should ask if the patient has traveled to such an area before making a diagnosis.

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