When a Tick Bite Mimics a Stroke: PCR-Confirmed Ehrlichial Meningoencephalitis Presenting with Expressive Aphasia and a Hyperferritinemic Syndrome

Background

Human monocytic ehrlichiosis, caused by Ehrlichia chaffeensis, is a tick-borne infection classically associated with fever, leukopenia, and thrombocytopenia. Neurologic involvement is uncommon but may present with focal deficits mimicking acute stroke. We report PCR-confirmed ehrlichial meningoencephalitis presenting with acute expressive aphasia, inflammatory cerebrospinal fluid findings, profound hyperferritinemia, and concern for secondary hemophagocytic lymphohistiocytosis (HLH).

Case Presentation

A 68-year-old retired nurse with a history of right breast cancer status post lumpectomy and lymph node dissection, chronic hepatitis C, hypertension, and gastroesophageal reflux disease presented with fever (102.8°F), altered mental status, and acute expressive aphasia, prompting a stroke alert. Several days earlier, she had received trimethoprim-sulfamethoxazole for presumed urinary tract infection and subsequently developed a transient rash. CT head, CT angiography, CT perfusion, and brain MRI showed no acute cerebrovascular abnormality. Further history revealed a tick bite during travel in New Jersey approximately three weeks before symptom onset. Laboratory studies demonstrated leukopenia, anemia, severe thrombocytopenia (nadir 36,000/μL), ferritin 13,858 ng/mL, and hypofibrinogenemia, raising concern for secondary HLH. CSF demonstrated 153 WBC/μL with 97% mononuclear cells and protein 130 mg/dL, consistent with inflammatory meningoencephalitis. Whole-blood E. chaffeensis PCR was positive. Babesia testing was negative, and Lyme disease was excluded by negative PCR and serologic/CSF antibody index testing. EBV IgM and IgG positivity was considered a possible cofactor rather than confirmed acute coinfection.

Findings

The patient was treated with doxycycline and supportive care. Empiric ceftriaxone was initially administered because of concern for neuroborreliosis and discontinued after negative Lyme testing. She demonstrated rapid clinical improvement, with resolution of fever and altered mental status and complete resolution of expressive aphasia. Platelet count recovered to 214,000/μL. Given the marked clinical and hematologic response to antimicrobial therapy, HLH-directed treatment and bone marrow biopsy were deferred.

Discussion & Conclusion

Ehrlichial meningoencephalitis can present as a stroke mimic and should be considered in patients with acute neurologic deficits, fever, cytopenias, and relevant tick exposure, particularly when neuroimaging is unrevealing. Profound hyperferritinemia and hypofibrinogenemia may suggest secondary HLH; however, rapid improvement with antimicrobial therapy may support infection-driven hyperinflammation rather than primary HLH and guide decisions regarding invasive evaluation and immunosuppressive therapy. Early recognition and prompt doxycycline treatment are critical, as neurologic disease may be severe but reversible.