Borrelia burgdorferi infection (
Lyme disease) is frequently accompanied by CNS dysfunction. Particularly common is a mild confusional state, the mechanism of which is unknown. Since CNS infection with B burgdorferi is usually accompanied by intrathecal synthesis of specific antibody, we studied CSF in 73 patients referred for presumed CNS
Lyme, manifested primarily as this confusional state. Of 30 seropositive patients evaluated, only 5 had intrathecal antibody production. Seven seronegative patients had positive cell-mediated immune responses to B burgdorferi in the peripheral blood; none had antibody production in the CSF. Of the remaining 36 patients referred with this diagnosis despite negative serologic studies, none had compelling evidence of CNS infection by this criterion. We conclude that CNS infection with B burgdorferi does occur in a small proportion of seropositive patients with this confusional state but is extremely uncommon among seronegative individuals with this clinical presentation.