Polymerase Chain Reaction-Confirmed Lyme Neuroborreliosis Masked by Pseudomonas Mastoiditis in a Mexican Traveler: A Case Report

Lyme borreliosis is seldom suspected in Mexico, yet vectors and human cases have been documented, and climate‑driven range expansion is predicted. We report a 67‑year‑old Mexican woman who, four months after suboptimally treated right‑sided otitis media, developed ipsilateral facial palsy, followed by episodes of fluctuating consciousness and cognitive impairment, suggestive of encephalopathy and rapidly progressive paraparesis. Imaging demonstrated destructive mastoiditis with a post‑sternocleidomastoid abscess from which <i>Pseudomonas aeruginosa</i> was cultured. Despite adequate surgical drainage and broad-spectrum antibiotic therapy, the patient's neurological status continued to deteriorate. Although cerebrospinal fluid (CSF) parameters remained within normal limits, intravenous ceftriaxone led to rapid stabilization of cognitive function, prompting reevaluation for a possible tick-borne etiology. Retrospective history revealed travel to San Antonio, Texas, 24 months earlier. <i>Borrelia burgdorferi</i> DNA was detected in CSF by polymerase chain reaction (PCR), and serum IgG was positive, fulfilling the guideline criteria for definite Lyme neuroborreliosis. A six‑week course of ceftriaxone, followed by oral doxycycline, led to near‑complete neurological recovery, except for persistent facial paresis. This case underscores three teaching points: (1) Lyme neuroborreliosis should enter the differential diagnosis of subacute cranial neuropathy and radiculomyelitis even in so‑called non‑endemic regions when travel or ecological change is plausible; (2) CSF may be normal and PCR sensitivity is low, yet a positive result is highly specific and can be decisive; and (3) superimposed nosocomial infections, here a pseudomonal mastoid abscess, may obscure the underlying vector‑borne disease and delay targeted therapy. Heightened clinical vigilance and adherence to diagnostic algorithms are essential to prevent irreversible disability as the geographic footprint of <i>Ixodes</i> ticks widens.