Introduction: Human granulocytic anaplasmosis (HGA) is a tick-borne infection endemic to the Midwest and Northeast United States. HGA infection results in hospitalization most commonly due to dyspnea or acute kidney injury in approximately 36% of cases. ICU admission is required in 17% for septic shock or respiratory failure with a mortality rate ranging from 0.3% to 0.6%. While CNS involvement of HGA is rare, it has been associated with seizures and ischemic infarcts. The following case discusses a rare presentation of HGA-associated encephalopathy and seizures.
Description: A 61-year-old man presented with 2 days of fevers and hallucinations. A few weeks prior, he reported spending time in a grassy field in northern Illinois. He was febrile to 39.9°C with labs notable for leukopenia, thrombocytopenia, hyponatremia, and transaminitis. Initial infectious workup was unrevealing. He was empirically started on piperacillin and tazobactam.
Two days after admission, the patient became agitated and confused. Neurologic exam otherwise revealed no focal deficits. MRI brain showed no acute findings. Given concern for CNS infection, a lumbar puncture was performed, but was noninfectious.
Subsequently, an engorged tick was identified on his back and IV doxycycline and ceftriaxone were started. A serum tick-borne PCR panel returned positive for Anaplasma phagocytophilum. Video EEG revealed multiple focal electrographic seizures arising from the left centro-temporal region. Levetiracetam, lacosamide and a benzodiazepine taper were required to obtain seizure freedom. His cognition and lab abnormalities significantly improved and he was discharged home after completing a 10-day course of doxycycline.
Discussion: Neurologic manifestations of HGA are rare. In our case, the patient developed refractory focal seizures despite no acute findings on serial neuroimaging. Early identification of a tick in high-risk patients and empiric antibiotic therapy is critical for favorable outcomes. Clinicians should also assess for possible coinfections, which are more commonly associated with neurologic abnormalities. In endemic regions, HGA should remain on the differential in patients with nonspecific systemic symptoms and new-onset neurologic findings.
