Lyme disease is a common cause of acute arthritis in children in endemic areas. Lyme arthritis responds readily to oral antibiotic management. The difficulty in the evaluation of Lyme arthritis is its clinical similarity to septic arthritis, especially when a patient presents with a single, swollen joint. Although serologic analysis is critical in identifying Lyme arthritis, obtaining these tests often results in a delay in diagnosis and sometimes unneeded surgical I & D. Therefore, the aim of this study was to develop a clinical algorithm to help differentiate Lyme arthritis from septic arthritis, with special attention given to ankle involvement and polyarticular involvement [2, 3].
Kocher identified four factors that could be used to distinguish septic arthritis from transient synovitis of the hip; these included fever >38.5, WBC >12, ESR >40, and an inability to bear weight on the affected leg. Kocher found that if 4/4 criteria were identified, the patient had close to a 99 % chance of having a septic process of the hip . In contrast, if a patient had one out of four criteria, the likelihood of septic process of the hip decreased to 3 %.
Data from the present study, in the context of Kocher’s criteria, revealed that only three patients were found to have a fever >38.5 at the time of presentation. Ten patients (10/39, 25.6 %) had a WBC >12. Although multiple studies have demonstrated that the ESR is elevated in Lyme disease, only 15 patients (15/39, 38.5 %) were found to have values >40 (Table 4). Additionally only 9/39, or 22 %, had pain with passive range of motion. On the other hand, pain with passive range of motion (PROM) is a hallmark of septic arthritis .
In the present study, we applied the Kocher criteria to patients with ankle and polyarticular involvement. We found that no patients had 4/4 Kocher criteria. Four patients had 3/4 Kocher criteria, and four patients had 2/4 Kocher criteria. Ten patients had 1/4 Kocher criteria, and 21 patients had 0/4 Kocher criteria. Although the Kocher criteria was developed for evaluating the pediatric hip, data from the present study suggest that these criteria are useful for differentiating Lyme from septic arthritis when the ankle and multiple joints are involved. In the current cohort of patients, the lack of Kocher criteria indicated the absence of a bacterial infectious process.
A recent multivariate analysis by Milewski in a Lyme-endemic area indicated that refusal to bear weight is the most predictive factor of septic arthritis . Prior reports in the literature also suggested that refusal to bear weight is an important predictive factor of septic arthritis [6, 7]. This is consistent with the results of the present study. Furthermore, we concur with Culp that refusal to bear weight is rare with Lyme disease; in our study, only two patients (2/39, 5.1 %) with Lyme disease of the ankle refused to bear weight. However, these two patients did not have pain with passive range of motion, which indicated Lyme arthritis rather than septic arthritis. In the present study, the presence of pain with passive motion was seen in six patients and an antalgic gait was seen in 11 patients .
An algorithm to differentiate Lyme disease from septic arthritis may minimize the number of patients who undergo surgical debridement when the diagnosis is not clear. For example, in a 2011 study by Milewski, 40/123 (~24 %) cases of Lyme arthritis underwent operative debridement for presumed septic arthritis . In our study, one patient (number 14) underwent surgical debridement, who was later found to have positive Lyme titers. This patient was subsequently managed with oral antibiotics. The low operative rate (2.5 %) in this study highlights the importance of the need to differentiate between Lyme and septic arthritis.
Williams reported that about 2/3 of patients with Lyme disease present with multiple joint involvement (an average of 2.4 joints affected) . In addition, Williams reported that the ankle was the second most commonly affected joint, after the knee. We concur with Williams that the ankle was the second most commonly involved and report an even higher rate of polyarticular involvement of 94 %.
Comparative studies between Lyme disease and septic arthritis usually focus on a single joint involvement and often apply the Kocher criteria to monoarticular evaluation. In contrast, in the current study, we applied Kocher’s criteria to polyarticular Lyme disease, with emphasis on cases involving the ankle. The rate of isolated ankle involvement is uncommon. Our data indicate that only two (2/39) had isolated ankle involvement. Our data suggest that knee/ankle involvement was the most common combination of joints and was seen in 56 % of cases. The results of this study strongly suggest that this finding of polyarticular involvement indicates Lyme arthritis rather than septic arthritis. The sensitivity of polyarticular involvement related to Lyme disease was 97.4 %.
There are several salient points that our data affords for analysis. First, in the context of Kocher’s criteria, patients with Lyme disease rarely had an elevated temperature, an elevated ESR, an elevated WBC, or difficulty bearing weight. The lack of Kocher criteria was very suggestive of Lyme arthritis. Historical clues are unreliable, since only 17 % of our patients reported a tick bite and 31 % noted a rash. This lack of historical clues is consistent with previous reports in the literature .
We suggest the following algorithm to help differentiate between Lyme and septic arthritis. Patients with two or fewer Kocher criteria, polyarticular disease, an ability to bear weight, and minimal pain with passive range of motion are more likely to have Lyme disease and should be treated with appropriate antibiotics and careful follow-up while waiting for Lyme serology results. Patients with three or more Kocher criteria, monoarticular involvement, inability to bear weight, and pain with passive range of motion of the joint are more likely to have septic arthritis and should be treated with surgical I and D, cultures, and appropriate IV antibiotics, also while waiting for Lyme serology results.
Limitations include the retrospective design of the study from a single institution and the lack of a control group. This study is the first to evaluate the polyarticular nature of Lyme disease as a tool to help differentiate Lyme arthritis from septic arthritis. Although patients 14, 27, 30, and 33 demonstrated 3/4 Kocher criteria, the polyarticular nature of their presentation convinced the treating surgeon to manage the patients without surgery in three of four of these cases.
An additional limitation of this algorithm is its inability to differentiate Lyme arthritis from juvenile idiopathic arthritis, which can have a similar clinical presentation . The mainstay of differentiating between Lyme and JIA is serologic testing. This is of particular importance in Lyme-endemic regions [10, 11].