Severe Thrombocytopenia and New Right Bundle Branch Block in Human Granulocytic Anaplasmosis: A Case Report

Human granulocytic anaplasmosis is an emerging tick-borne illness caused by Anaplasma phagocytophilum and transmitted by Ixodes ticks. Clinical manifestations are often nonspecific, including fever, malaise, and cytopenias, which can delay recognition and treatment. Although thrombocytopenia is common in human granulocytic anaplasmosis (HGA), profound thrombocytopenia is rarely described, and cardiac conduction abnormalities remain infrequently reported. We describe a 73-year-old woman in New England who developed fever, somnolence, acute kidney injury, transaminitis, a platelet nadir of 12 × 10 9 / L ( 168 – 382 × 10 9 / L ) , and a new right bundle branch block (RBBB) with modest troponin elevation. Peripheral smear revealed Döhle bodies, vacuolated neutrophils, and giant platelets. Respiratory viral panel and blood cultures were negative. Polymerase chain reaction (PCR) confirmed A. phagocytophilum . The patient was initially treated empirically with atovaquone and azithromycin for presumed babesiosis, but therapy was narrowed to doxycycline with rapid recovery of symptoms and normalization of laboratory abnormalities. No echocardiogram or repeat electrocardiogram was performed during hospitalization despite the new conduction abnormality and elevated troponin, limiting conclusions regarding causality. This case underscores the need for heightened clinical suspicion in endemic regions, highlights an unusual severity of thrombocytopenia, and raises questions regarding potential cardiac involvement after the incidental finding of a new right bundle branch block.