NEW YORK (Reuters Health) Results of a retrospective study confirm that the Rule of 7’s prediction tool accurately identifies children who are unlikely to have Lyme meningitis, investigators report in Pediatrics released online December 19.

Children at low risk may be considered for outpatient management while awaiting Lyme serology, they advise.

Dr. Lise E. Nigrovic, with Children’s Hospital in Boston, Massachusetts, and colleagues point out that serology for Borrelia burgdorferi can take several days so deciding whether to hospitalize children with suspected Lyme meningitis in order to start empiric parenteral antibiotics can be difficult.

A prediction rule known as the Avery equation was developed to identify children at low risk for Lyme meningitis, based on headache duration, presence of cranial neuritis, and percentage of cerebrospinal fluid mononuclear cells, the authors explain. A simplified version, the Rule of 7’s, is based on three criteria: headache for less than 7 days, less than 70% mononuclear cells in CSF, and absence of seventh nerve or other cranial nerve palsy.

The team tested the performance of the two prediction tools in a retrospective study of 423 children with CSF pleocytosis seen at three emergency departments in an area where Lyme disease is endemic. Among this cohort, 117 (28%) had Lyme meningitis, 306 (72%) had aseptic meningitis, and none had bacterial meningitis.

The team found that the Rule of 7’s actually performed better than the more complicated Avery regression equations.

The Rule of 7’s classified 130 of the 419 children with adequate prediction data as low risk, of whom 5 actually had Lyme meningitis. This translated to a sensitivity of 96% (ie, 112/117) and a specificity of 41% (125/302).

One of the hallmarks of Lyme disease, erythema migrans, was absent in 390 children, 85 of whom did have Lyme meningitis. The sensitivity and specificity of the Rule of 7’s were the same within this group, Dr. Nigrovic and colleagues report.

Patients classified as low risk by using either the Avery clinical prediction rule or the Rule of 7’s were unlikely to have Lyme meningitis, they conclude. The Rule of 7’s was considerably simpler to apply and performed better in our multicenter validation cohort.

Reference:

www.pediatrics.org/cgi/doi/10.1542/peds.2011-1215

Pediatrics 2012;129.