Water on the Knee' Could Be a Sign of This Disease

The bull's-eye rash that develops after a tick bite might be the most common, well-known sign of a Lyme disease infection, but one study is reminding doctors of a more obscure thing to watch out for.

"Water on the knee," or "spontaneous knee effusion" as they called it, could present itself in a Lyme disease case even without the more traditional bull's-eye rash. The researchers are saying that this swelling around the knee joint could be used to help identify a case of Lyme disease and begin treatment before more serious symptoms develop.

"It is important to catch and treat Lyme disease early because the symptoms get progressively worse over time," Dr. Elizabeth Matzkin, assistant professor of orthopaedic surgery at Harvard Medical School, said in a statement. "However, the lab tests used to diagnose Lyme disease can take time to process, and there are certain circumstances in which immediate antibiotic treatment may be recommended before the lab results are complete."

The study suggests doctors consider testing for Lyme disease when they diagnose knee effusion, especially if they are in areas with ticks carrying the bacteria are common. (Photo credit: Shutterstock)

"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," Matzkin, lead author of the literature review published in the Journal of the American Academy of Orthopaedic Surgeons, continued. "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."

The study authors suggest that doctors keep Lyme disease in mind as a possible cause of spontaneous knee effusion when they are issuing such a diagnosis and test for it accordingly.

According to the Centers for Disease Control and Prevention, there are about 30,000 Lyme disease cases reported each year, but it believes over 300,000 cases are diagnosed in the country. Lyme disease is a bacterial infection caused, most commonly, by Borrelia burgdorferi, which is transmitted by ticks. It can cause "fever, chills, headache, fatigue, muscle and joint aches, and swollen lymph nodes."

If not treated early on, more severe symptoms of the disease range include rashes, severe joint pain, inflammation of the brain and spinal cord, heart problems and more.

In addition to the bull's-eye rash and swollen knees, the CDC says facial palsy, or paralysis of facial muscles, could be a sign as well.

Possible signs of Lyme disease. (Image source: CDC)

In most cases, Lyme disease can be treated successfully with antibiotics.