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Differentiating Lyme Disease from Septic Arthritis
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Posted on: 11/30/1999
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Children who come to the hospital or clinic with a swollen knee in areas where Lyme disease is common must be evaluated carefully. Symptoms of Lyme arthritis are similar to septic (infectious) arthritis and the treatment for these two conditions is different.
Efforts are being made to collect data that will help physicians make an early and accurate diagnosis based on clinical presentation. If the most common signs and symptoms of each condition could be categorized, a clinical diagnosis (without accurate blood tests) might be possible. This is important because septic or infectious arthritis is often a surgical emergency to prevent joint destruction. Lyme arthritis requires treatment but it is not an emergency.
One way to gain an understanding of the differences between these two forms of knee arthritis is to take a look back at medical records. Comparing children with Lyme arthritis versus those who ended up with septic arthritis helps classify similarities and differences. This type of study is referred to as a retrospective analysis.
In this retrospective study, physicians at the Yale University School of Medicine went through all the records of children (ages up to 18 years old) admitted for knee swelling.
Anyone who had a diagnostic aspiration (removal of synovial fluid from inside the joint) was included. The patients who had a positive culture for septic arthritis (13 per cent) were put in one group. The children with Lyme arthritis (31 per cent) were part of the second group. The rest of the children had neither septic nor Lyme arthritis and were then excluded from further evaluation.
Characteristics of the patients remaining were compared using blood lab results and clinical presentation. Lab values included white blood cell count, erythrocyte sedimentation (sed) rate, C-reactive protein (CRP), Lyme titers, and joint fluid cell count. Signs and symptoms compared between the two groups included fever, refusal to put weight on the leg, and swelling and warmth of the knee.
They found two major differences between the groups: children with septic arthritis were more likely to have a significant fever (higher than 101.5 degrees Fahrenheit) and refused to put weight on the affected leg. Neither one of these symptoms was part of the clinical presentation of Lyme disease.
There was no difference between the two groups based on sed rate or C-reactive protein (indicators of inflammation). Children with septic arthritis were 3.6 times more likely to have high levels of synovial fluid cell count.
Children with septic arthritis were also four times more likely to have elevated white blood cells compared with children who had Lyme arthritis. But these tests were not used to make a definitive diagnosis because some children with Lyme disease also had high levels as well.
The researchers also took a look at which joints were affected in both groups. Everyone had a knee problem. But some children in both groups had more than one joint involved. Septic arthritis had the greatest percentage over Lyme disease for hip, ankle, elbow, and shoulder.
In summary, this Connecticut-based study (a place where Lyme disease is very common), showed that the two strongest predictors for a diagnosis of septic knee arthritis were fever and refusal to put weight on the leg.
Children with knee pain and swelling associated with Lyme disease are more likely to have lower white blood cell counts, lower joint fluid cell count, and lower body temperatures compared with children who have septic knee arthritis.
Physicians will find this information useful when trying to diagnose between septic arthritis and Lyme disease for children with knee pain and swelling. The distinction is important because septic arthritis can cause rapid destruction of knee joint cartilage and must be stopped quickly. In both cases, an accurate diagnosis is needed to direct treatment and prevent long-term complications.
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References:
Matthew D. Milewski, MD, et al. Lyme Arthritis in Children Presenting with Joint Effusions. In The Journal of Bone and Joint Surgery. February 2011. Vol. 93. No. 3. Pp. 252-260.
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*Disclaimer:*The information contained herein is compiled from a variety of sources. It may not be complete or timely. It does not cover all diseases, physical conditions, ailments or treatments. The information should NOT be used in place of visit with your healthcare provider, nor should you disregard the advice of your health care provider because of any information you read in this topic. |
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