Hemophagocytic Lymphohistiocytosis Due to Ehrlichiosis: A Case Series.

Background: Hemophagocytic lymphohistiocytosis (HLH) is an immunologic syndrome characterized by excessive inflammation and tissue injury due to uncontrolled activation of the phagocytic system. The underlying mechanism is a lack of downregulation of activated macrophages and lymphocytes by natural killer and T cells. Unfortunately, the diagnosis is often delayed or missed due to the rarity of the disease, decreased awareness, and clinical picture variability. Ehrlichiosis is becoming a more prevalent tick-borne illness in endemic regions and a relatively uncommon but increasingly considered cause of HLH.

Case Presentation: We describe the cases of 2 patients diagnosed with secondary HLH as per the 2004 HLH criteria, with the trigger secondary to ehrlichiosis. Our first patient presented with a febrile illness and a remarkably elevated blood ferritin concentration. He ended up meeting HLH criteria despite having a negative bone marrow biopsy. Patient 1 had significant clinical improvement in vitals and had a down-trending ferritin with steroids, doxycycline, and intravenous immunoglobulin. The second patient presented with severe systemic involvement and hemodynamic instability. She was found to have HLH with a positive bone marrow biopsy and a positive Ehrlichia PCR. Patient 2 had significant improvement in her hemodynamic instability with the use of anakinra and doxycycline.

Conclusion: Raising awareness about HLH is imperative for early diagnosis and trigger-directed treatment, which can help in preventing the disease's severe complications. There are an increased number of reports of Ehrlichiosis progressing to HLH. Early identification and treatment with doxycycline, with the use of immunomodulatory treatment in severe cases, has shown favorable outcomes.