Dengue-Associated Secondary Hemophagocytic Lymphohistiocytosis Presenting as Persistent Cytopenia: A Case Report.

Hemophagocytic lymphohistiocytosis (HLH) is a rare but life-threatening hyperinflammatory syndrome caused by uncontrolled immune activation and increased release of pro-inflammatory cytokines, resulting in multiorgan dysfunction. Secondary HLH is often activated by infections, especially viral infections. Dengue fever, the most common arboviral infection in tropical regions, is an uncommon but known precipitating factor of HLH and continues to challenge diagnosis due to overlapping clinical and laboratory manifestations. We describe the case of a 23-year-old previously healthy woman who presented with high-grade fever, abdominal pain, and progressive cytopenias. Laboratory investigations demonstrated pancytopenia and elevated hepatic transaminases. Dengue IgM serology was positive, and other infectious etiologies were ruled out. Despite supportive management, the patient had persistent fever and deteriorating hematological parameters. Additional blood workup showed elevated serum ferritin, hypertriglyceridemia, hypofibrinogenemia, and increased D-dimer levels. Bone marrow examination showed hemophagocytosis, meeting five out of eight diagnostic criteria for HLH, hence confirming the diagnosis of dengue-associated secondary HLH. She was successfully treated with intravenous dexamethasone and gradual oral tapering that led to clinical improvement and recovery of hematological parameters. Early identification and rapid initiation of immunosuppressive therapy were key to preventing further clinical decline. This case underscores the need for a high index of clinical suspicion for HLH in patients with dengue infection presenting with febrile illness, progressive pancytopenia, and elevated ferritin levels. Differentiating severe dengue from dengue-associated HLH early is crucial because their treatment regimens vary. Early diagnosis and appropriate corticosteroid therapy can improve patient prognosis.