Patients who are classified as low risk for Lyme meningitis using the
“Rule of 7’s” clinical prediction tool may be managed as
outpatients, but patients should still be closely monitored until serology data
become available, according to a study published online.
Keri A. Cohn, MD, of Children’s Hospital Boston, and
colleagues said the Rule of 7’s is a useful predictive tool in screening
for whether to hospitalize children while awaiting serology results.
The Rule of 7’s classifies children at low risk for Lyme meningitis
when each of the following three criteria are met: less than 7 days of
headache; less than 70% cerebrospinal fluid (CSF) mononuclear cells; and
absence of seventh or other cranial nerve palsy.
In the retrospective study, Cohn and colleagues tested the efficacy of
the Rule of 7’s on a multicenter cohort of 423 children presenting with
symptoms of CSF pleocytosis at children’s hospitals based in Boston,
Wilmington, Del., and Philadelphia.
The researchers said among 423 children, 117 had Lyme meningitis, 306
had aseptic meningitis and none had bacterial meningitis. Only five of 130
children who were classified as having a low risk under the Rule of 7’s
had Lyme meningitis.
“The Rule of 7’s performed better and was considerably easier
to apply than the Avery predictive model, which required a complicated
mathematical calculation to estimate the probability of Lyme meningitis,”
the researchers wrote. “The Rule of 7’s also performed well in the
subgroup of patients with occult Lyme disease (ie, no physician-documented
[erythema migrans] rash).”
The researchers said there were some study limitations; notably, the
study’s retrospective design, which may have limited access to medical
records or clinical predictors. Regardless, treating those patients classified
as low risk may reduce unnecessary antibiotic use and hospitalizations.
Disclosure: The researchers report no relevant financial
disclosures.
Eugene Shapiro, MD
The goal of this study is admirable: to assess the validity of the
“Rule of 7’s” to identify which children in areas endemic for
Lyme disease who present with what appears to be aseptic meningitis are at low
risk of actually having Lyme meningitis.
However, the investigators used an unreliable definition for which
patients had Lyme meningitis. Patients with pleocytosis and positive serology
in the peripheral blood for either immunoglobulin M or IgG antibodies to
Borrelia burgdorferi were classified as having Lyme meningitis. It is
well recognized that the criteria for positive IgM serology are not
sufficiently stringent and that false-positive results are common, yet nearly
half of the patients with Lyme meningitis had a positive IgM alone. Moreover,
most experts would not accept positive serology in the blood alone as evidence
of Lyme meningitis (antibody concentration in CSF is more of a gold standard).
Consequently, it is likely that the number of patients with Lyme meningitis in
this sample is substantially overestimated, which makes the conclusions of the
investigators subject to uncertainty.
While it is likely that patients in the low-risk category are indeed at
low risk of Lyme meningitis, the implication that the larger number of subjects
not in the low-risk category should be hospitalized and treated for possible
Lyme meningitis is disturbing. Not only is it likely that a majority of these
patients do not have Lyme meningitis, but also there is now good evidence from
clinical trials in Europe that Lyme meningitis can be treated effectively with
doxycycline administered orally.
- Eugene Shapiro, MD
Infectious Disease
News Editorial Board member
Disclosure: Dr. Shapiro reports no relevant
financial disclosures.