The hemophagocytic lymphohistiocytosis (HLH) is a syndrome with apoptosis deficiency that results in the impairment of a regulatory pathway with consequent immune and inflammatory responses. Fever, cytopenias, splenomegaly, and hemophagocytosis are cardinal signs. It may be familial or secondary to infection, autoimmunity, or neoplasia. Impaired natural killer (NK)-cell cytotoxicity is the hallmark of HLH. All genetic defects in familial HLH are related to granule-dependent cytotoxicity.

The authors present a 35-year-old male veterinary technician with no prior comorbidities who presented with a history of continuous high-grade fever for 20 days associated with chills, rigors, and generalized weakness. There were no associated respiratory, gastrointestinal, or neurological symptoms. On examination, he was hemodynamically stable with icterus and perioral crusted rashes, and abdominal examination revealed hepatomegaly and splenomegaly.

Initial laboratory evaluation demonstrated cytopenias (leukopenia and thrombocytopenia), markedly elevated inflammatory markers, deranged liver function tests, and extreme hyperferritinemia (250,000 ng/mL) with hypertriglyceridemia (705 mg/dL). Ultrasonography of the abdomen confirmed hepatosplenomegaly.

Based on clinical features and laboratory parameters fulfilling diagnostic criteria, the patient was diagnosed with secondary hemophagocytic lymphohistiocytosis (macrophage activation syndrome).