The authors of this Level-II study have presented us with the largest review to date in which Lyme disease-induced joint effusions were compared with septic arthritis. However, this contribution is more than just a comparison of two disease entities; it is an in-depth analysis of the effects of the increasing presence of Lyme disease in the endemic areas of North America. The reason why this analysis is important is that Lyme disease, since its discovery by Steere et al. in 1977, is caused by the spirochete Borrelia burgdorferi and is now the most common tick-borne disease in the United States. As the spirochete can be effectively treated with antibiotic administration, the accurate diagnosis of Lyme disease becomes more important to avoid an unnecessary surgical arthrotomy for the child.
Although the authors tried to definitively distinguish between Lyme disease and septic arthritis with the goal of creating a reliable algorithm in order to enable us all to have a gold standard to differentiate the two, they were unable to do so. In their quest to do so, however, they demonstrated that a diagnosis of septic arthritis is more probable in children presenting with an inability to bear weight, a fever of >101.5°F (>38.6°C), an elevated peripheral white blood cell count of >10.3 × 1000/µL, and a synovial fluid nucleated cell count of >100,000 cells/mm3. However, there is still an overlapping gray zone where the only diagnostic test that will separate the two similar clinical presentations is serological testing of the synovial fluid aspirate for Lyme disease.
Herein lies another important contribution of this paper. In endemic areas in the Northeast, Upper Midwest, and Pacific Northwest of the United States, all children with unexplained, nontraumatic joint effusions should have a joint aspiration followed by serological testing for Lyme disease. Why? Because in these areas, the incidence of Lyme disease has risen 101% over the last fifteen years. Also, once Lyme disease has been diagnosed, antibiotic treatment with use of amoxicillin for patients with an age of less than eight years and with use of doxycycline for those with an age of eight years or more is curative. As synovial involvement is a late manifestation of the disease, morbidity resulting from the involvement of other organs, especially chronic encephalopathy and keratitis, should be ruled out. The authors also reported that 31% of all children who had a joint aspiration were found to have Lyme disease on the basis of serological testing. This high percentage in itself emphasizes the importance of aspirating joint effusions at the time of presentation to the emergency department in endemic areas.
This review also has highlighted a technical deficiency inhibiting our handling of Lyme disease—specifically, the fact that results of serological testing may take up to a week to obtain. We obviously need a quicker Lyme disease test if we are to avoid arthrotomies in children presenting with high synovial cell counts. In this series, 24% of children with Lyme disease and synovial cell counts of >100,000 cells/mm3 underwent an unnecessary arthrotomy simply because one cannot wait for a week for the results of the Lyme test if septic arthritis is suspected. A corollary to this is that, in an endemic area, the diagnosis of both septic arthritis and Lyme disease must be considered even for children with synovial cell counts of >100,000 cells/mm3. In many studies of septic arthritis, as many as 40% of patients have negative cultures. In endemic areas, undoubtedly some of these patients had Lyme disease.
This paper showed no difference between children with Lyme disease and those with septic arthritis with regard to either the erythrocyte sedimentation rate or the C-reactive protein level. The data presented by the authors also indicate that we may not be diligent enough in pursuing the diagnosis of Lyme disease as serological testing was performed for only 64% of the patients who underwent joint aspirations in their hospital. Those of us practicing in endemic areas should ensure that our own hospital emergency departments are sending all joint aspirations for serological testing for Lyme disease routinely. An additional interesting finding was that Lyme disease presents throughout the entire year, and not just when the ticks are biting. Hence, we need to be as diligent in our pursuit of the diagnosis of Lyme disease in January as in July as its onset may be delayed weeks or months after the precipitating tick bite.
Although this was a retrospective study from a single institution, it demonstrates the value of a well-done study concentrating on a specific entity. This well-documented study has increased our awareness of Lyme arthritis and has pointed out to those of us practicing in endemic areas how we can all improve our diagnosis and treatment of children presenting with a swollen joint due to Lyme disease.