Lyme disease remains the most common vector-borne disease in North America. This academic teaching case highlights a full diagnostic workup fueled by anchoring bias, resulting in a presumptive diagnosis of early disseminated Lyme meningitis. Patient report of direct tick exposure, neurocranial defects, and equivocal serologies, despite geographic region of low pretest probability, confounded the clinical picture. Infectious workup confirmed the true diagnosis to be aseptic meningitis due to enterovirus. This clinical vignette acknowledges the habitual anchoring biases in the daily decision-making among internists and trainees contributing to misdiagnoses and subsequently, overtreatment.
Keywords: anchoring bias; borrelia; false positive; immunoblot; lyme disease; tickborne diseases; ticks.