Anti-Borrelia Antibody Index Insufficient to Diagnose Lyme Neuroborreliosis
By Will Boggs, MD
NEW YORK (Reuters Health) Sept 11 - By itself, the intrathecal anti-Borrelia antibody index
(AI) is inadequate to diagnose Lyme neuroborreliosis, according to a report in the September
4th Neurology.
"The antibody index has a very good specificity (97%) but only a moderate sensitivity (75%),"
Dr. Frederic Blanc from University Hospital of Strasbourg, France told Reuters Health.
Dr. Blanc and colleagues assessed the value of AI in diagnosis of neurologic manifestations
of neuroborreliosis among patients with CSF anti-Borrelia antibodies. Based on their findings,
they proposed intermediate criteria to diagnose neuroborreliosis.
The AI was calculated by dividing the ratio of ELISA titer in CSF/ELISA titer in serum by the
ratio of total IgG in CSF/total IgG in serum.
Among 40 patients with definite neuroborreliosis, the AI was positive in 30 (i.e., 75%
sensitivity), intermediate in 6, and negative in 4, the authors report.
The AI was positive in only 2 of 74 patients with another etiologic diagnosis, for a specificity
of 97%. It was intermediate in 10 patients and negative in 61 patients.
Because of the lack of sensitivity of the AI, the investigators propose that a diagnosis of
neuroborreliosis be made only when at least 4 of the following 5 items are present: no past
history of neuroborreliosis; CSF anti-Borrelia antibodies; positive anti-Borrelia antibody index;
favorable outcome after specific antibiotic treatment; and no other etiologic diagnosis.
"Positive Lyme serology in the CSF does not mean neuroborreliosis," Dr. Blanc explained,
"because among 123 patients with positive Lyme serology in the CSF, only 40 had a real
neuroborreliosis."
"The anti-Borrelia AI can be used to determine if a seropositive patient with nonspecific
symptoms in whom the clinical suspicion of neurologic Lyme disease is low needs to be
treated," write Dr. Karen L. Roos from Indiana University School of Medicine, Indianapolis,
Indiana and Dr. Joseph R. Berger from University of Kentucky College of Medicine,
Lexington, in a related editorial.
"If the AI is less than 2," they continue, "the evidence favors not treating the patient."
"In my point of view, patients with neurological symptoms and positive antibody index,
without any history of neuroborreliosis, have to be treated," Dr. Blanc concluded. "If the
antibody index is negative, the clinician has to search for another etiology."
Neurology 2007;69:953-958,949-950.