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Joint Pain in Kids Much More Likely Lyme Disease than Septic Arthritis (at least in Lyme endemic regions)

lyme arthritis in children vs septic arthritisA newly published article looking at arthritis in children has found that those with pain in one knee (monoarthritis) are more likely to be suffering from Lyme disease and Lyme arthritis than septic arthritis, at least if they live in an area known to be rife with Lyme disease infection. The new research offers physicians guidance on testing such pediatric patients in order to avoid painful, invasive diagnostic procedures. The authors caution, however, that such guidelines are only appropriate for Lyme-endemic areas and that septic arthritis should still be ruled out in areas where Lyme disease is unlikely.

Avoiding Painful Medical Procedures

The 673 children whose results were assessed in this study and who had an absolute neutrophil count of 10 × 103 cells/mm3 or higher, and an erythrocyte sedimentation rate (ESR) of 40 mm/hour or higher were deemed not to require arthrocentesis. What this means for physicians is that, in Lyme-endemic areas, patients meeting the above criteria can go without arthrocentesis (drainage of the joint fluid for testing purposes), parenteral antibiotics and surgical irrigation of the knee joint as it is significantly more likely that they have Lyme arthritis than septic arthritis. Treating septic arthritis requires draining of the accumulated infected fluid in the joint, the use of oral or intravenous antibiotics for four to six weeks (usually), and arthroscopy to remove infected tissue. Some patients also require the joint to be immobilized so as to reduce pain.

Lyme Likeliest Cause of Knee Arthritis in Lyme-Endemic Regions

The children included in this study had septic arthritis in 3% of cases, Lyme arthritis in 51% of cases and another kind of inflammatory arthritis in the remaining 46% of cases. It is often difficult to connect such joint pain with a tick bite as many months can pass before these symptoms of Lyme disease arise. Parents may recall their child having a flu-like episode prior to the arthritis developing, although the various coughs and sniffles and infections children are exposed to at school can make it difficult to recall such illnesses clearly. Children were ruled out of the study if they had suffered a specific knee injury, had previous knee surgery, knee cellulitis, rheumatoid arthritis or other immune system dysfunction, or where other joints were also painful.

Sepsis and Lyme Disease – Culture is Key

The research was carried out at Boston Children’s Hospital, giving the clinicians a plentiful supply of patients with Lyme disease. Patients seen in a different hospital, Yale – New Haven Hospital, also in a Lyme-endemic area, were used to validate the results of the study by taking the devised criteria and seeing how effective they were in determining the potential septic arthritis patients. Those children diagnosed with Lyme arthritis all had positive blood results for the infection whereas those with septic arthritis had synovial fluid (the fluid from the knee joint) positive for bacterial infection (or blood positive for bacterial infection accompanied by an additional test showing an increased cell count in the knee’s synovial fluid).

Causes of Septic Arthritis

The validation patients with the elevated ANC and ESR levels also had higher levels of C-reactive protein (a marker for inflammation), although clinical signs of arthritis in the children with Lyme disease and with septic arthritis were indistinguishable. Bacteria were able to be grown from the synovial fluid in all 19 cases of diagnosed septic arthritis; specific bacterial organisms included methicillin-sensitive Staphylococcus aureus, group A streptococcus, Streptococcus pneumoniae, and Enterobacter agglomerans.

Septic Arthritis vs. Lyme Arthritis – Risks and Treatment

Children presenting with symptoms of septic arthritis or Lyme arthritis in a Lyme endemic area may now be able to undergo a blood test that allows them to avoid unnecessary, painful procedures to drain the joint and retrieve a synovial fluid sample. Starting such patients on empirical antibiotics is the usual course of action, with specific antibiotics then administered when the infectious agent is determined. This can be bacterial, viral, or fungal, which affects the choice of treatment. Early medical attention is important in order to improve the likelihood of full recovery of joint function. Longstanding sepsis in the knee can cause permanent tissue damage.

Risk factors for septic arthritis include:

  • taking immune-suppression medicines
  • intravenous drug abuse
  • past joint disease, injury or surgery
  • diabetes
  • alcoholism
  • sickle cell disease
  • rheumatic diseases
  • immune deficiency disorders.

Clearly, some of these risks are unlikely to be relevant in children with suspected Lyme disease, but differentiating septic arthritis from Lyme arthritis may now, thanks to these new guidelines, be that little bit easier in a Lyme-endemic area.


Julia K. Deanehan, Amir A. Kimia, et al, Distinguishing Lyme From Septic Knee Monoarthritis in Lyme Disease–Endemic Areas, Pediatrics. Published online February 18, 2013.

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