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Rule of 7's Sensitive in ID'ing Low Risk of Lyme Meningitis

Clinical prediction rule classifies low-risk patients based on clinical and lab parameters

MONDAY, Dec. 19 (HealthDay News) -- The "Rule of 7's," a Lyme meningitis clinical prediction rule based on clinical and laboratory parameters, identifies children with cerebrospinal fluid (CSF) pleocytosis who are at low risk for Lyme meningitis with high sensitivity, according to a study published online Dec. 19 in Pediatrics.

Keri A. Cohn, M.D., from the Children's Hospital Boston, and colleagues tested the performance of the Rule of 7's among 423 children with CSF pleocytosis living in Lyme disease-endemic areas. The Rule of 7's classified children as low risk for Lyme meningitis if they had headaches for less than seven days, less than 70 percent CSF mononuclear cells, and absence of seventh or other cranial nerve palsy. The U.S. Centers for Disease Control and Prevention criteria were used to define Lyme meningitis (either positive Lyme serology test or an erythema migrans [EM] rash). Lyme meningitis was identified in 117 children, aseptic meningitis in 326 children, and bacterial meningitis in none. The performance of the Rule of 7's was calculated among 390 children without physician-documented EM, and in the whole study population.

The investigators found that 130 children were classified as low risk. Of these, five had Lyme meningitis, with a sensitivity and specificity of 96 and 41 percent, respectively. Of the 127 children without EM classified as low risk, three (2 percent) of these had Lyme meningitis.

"Patients classified as low risk by using the Rule of 7's were unlikely to have Lyme meningitis and could be managed as outpatients while awaiting results of Lyme serology tests," the authors write.

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