Cerebrospinal Fluid Findings among Patients with Anaplasmosis and Central Nervous Involvement, Minnesota and Wisconsin, USA.

Anaplasmosis, an emerging tickborne zoonosis, infrequently involves the central nervous system, and cerebrospinal fluid (CSF) profiles of anaplasmosis remain poorly characterized. We conducted a multisite retrospective study of patients hospitalized with anaplasmosis during November 1, 2014-November 29, 2024, in Minnesota and Wisconsin, USA, a hyperendemic region. Included patients had anaplasmosis confirmed by PCR on blood samples, exhibited neurologic symptoms, and had lumbar puncture procedures. Ten hospitalized patients met inclusion criteria, 6 with meningitis, 3 with meningoencephalitis, and 1 with encephalitis. CSF findings were within reference ranges for 5 patients; 4 patients demonstrated mild lymphocytic pleocytosis, but glucose and protein levels were within reference ranges. One patient underwent a traumatic lumbar puncture resulting in neutrophilic pleocytosis. CSF abnormalities did not correlate with neurologic severity, suggesting a cytokine-mediated process rather than direct central nervous system infection. All patients rapidly improved with doxycycline, highlighting the need for early recognition and empiric therapy for anaplasmosis.