Abstract Introduction Human granulocytic anaplasmosis (HGA) is a tick-borne illness caused by Anaplasma phagocytophilum. While it often presents as a mild, self-limiting febrile illness, severe complications such as hemophagocytic lymphohistiocytosis (HLH) can rarely occur, especially in immunocompromised hosts. We describe a case of HGA-associated HLH in a kidney transplant recipient. Case Presentation A 75-year-old male with ESRD s/p kidney transplant (2022) on tacrolimus and myfortic presented with three weeks of generalized weakness and fever, initially presumed to be related to a recurrent urinary tract infection based on prior similar episodes. His hospital course was complicated by acute hypoxic respiratory failure due to pneumonia and worsening encephalopathy requiring intubation. LP, MRI, and EEG were unremarkable. By hospital day 4, labs showed worsening thrombocytopenia, anemia, elevated liver and kidney enzymes, ferritin 7500 ng/mL, hypertriglyceridemia, elevated IL-2 receptor (12,916 U/mL), and splenomegaly (15.7 cm), raising concern for HLH. Peripheral smear revealed inclusion bodies. Empiric doxycycline was initiated on day 8, and PCR confirmed A. phagocytophilum; Ehrlichia serologies were negative. Dexamethasone was started for HLH. The patient improved with resolution of cytopenias and encephalopathy, was extubated on day 10, and bone marrow biopsy (day 11) showed emperipolesis but no definitive hemophagocytosis. He completed a 10-day doxycycline course with steroid taper, and immunosuppressants were resumed before discharge. Discussion HLH is a life-threatening hyperinflammatory syndrome caused by uncontrolled immune activation and cytokine release. Diagnosis requires meeting ≥5 of 8 criteria; this patient met five—fever, bicytopenia, hypertriglyceridemia, hyperferritinemia, and elevated soluble IL-2 receptor. Although bone marrow biopsy did not show definitive hemophagocytosis, this may have reflected biopsy delay or treatment effect.Anaplasmosis-associated HLH is exceedingly rare, with fewer than ten U.S. cases reported. Most occurred in older adults, and few in solid organ transplant recipients. HGA typically presents with fever, myalgias, and cytopenias, but in immunocompromised hosts, it can progress rapidly to severe disease or multiorgan failure. Transplant recipients are particularly vulnerable due to impaired immune responses and delayed diagnosis. Early recognition of tick-borne illness and prompt doxycycline therapy are crucial to prevent irreversible immune dysregulation. Conclusion Anaplasmosis-associated HLH is a rare but potentially fatal complication in transplant recipients. Early suspicion and timely doxycycline initiation are essential for favorable outcomes. This abstract is funded by: none
Lin et al. (Fri,) studied this question.