Thanks to a new test, US researchers have managed to conclude that septic arthritis is unlikely in children from Lyme disease–endemic areas who have knee monoarthritis, and have an absolute neutrophil count (ANC) of 10 × 103 cells/mm3 or higher, and an erythrocyte sedimentation rate (ESR) of 40 mm/hour or higher.
The study, which was reported in Paediatrics, was led by Julia K. Deanehan, MD, from the Division of Emergency Medicine, Boston Children’s Hospital and Harvard Medical School, Boston, Massachusetts, who said that ‘Laboratory criteria can be used to identify children with knee monoarthritis at low risk for septic arthritis who may not require diagnostic arthrocentesis.’ However, both the study authors and outside experts explain that this approach should not be generalised to patients from other areas, as it was developed using patients from areas with endemic Lyme disease.
673 patients were involved in the study, of whom 19 (3%) had septic arthritis, 341 (51%) of the participants’ wellness was affected by Lyme arthritis, and other inflammatory arthritis affected the wellbeing of 313 (46%) of those studied. According to study senior author Lise E. Nigrovic, MD, MPH, ‘We were surprised by the low incidence of knee septic arthritis. At the 2 study institutions with 21 study years (between the 2 institutions), we identified only 19 kids with knee septic arthritis.’
Dr Nigrovic is attending physician in the Division of Emergency Medicine and assistant professor of Paediatrics at Boston Children’s Hospital, and she explained that for children in Lyme-endemic areas who meet the ANC and ESR criteria, clinicians can safely bypass arthrocentesis, parenteral antibiotics, and surgical irrigation.
Karen Onel, MD, division chief for Paediatric Rheumatology and Associate Professor of Paediatrics at the University of Chicago, Illinois, who was not involved in the work, adds, ‘It is unclear how the criteria would hold up if the relative frequency of disease were more equal; that is, where both were rare diseases. And in that situation, if a few children with Lyme arthritis underwent arthrocentesis, it would have less significance than if all the children with Lyme arthritis in an endemic area needed the procedure.’
However, Susanna Esposito, MD, a paediatric infectious disease specialist at the University of Milan, Italy, affirms, ‘Data collected by these authors demonstrate that the use of ANC and ESR can be useful in identifying children with high or low risk of septic arthritis, and consequently in deciding whether arthrocentesis is mandatory or can be avoided.’
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