BACKGROUND: Hemophagocytic Lymphohistiocytosis (HLH) usually affects children, and it may present in a number of ways, and it may imitate a number of other diseases. If diagnosis is delayed, the disease may cause permanent disability or even be fatal. The diagnostic criteria are fever, splenomegaly, cytopenias, hypertriglyceridemia and/or hypofibrinogenemia and the histopathological finding of hemophagocytosis in bone marrow, spleen, or lymph nodes. Neurological complications usually appear late in the course, and are the most incapacitating sequelae in HLH. The course is severe, often fatal.

OBJECTIVES: We hereby report the first documented case of primary hemophagocytic histiocytosis which presented initially and predominantly as focal encephalitis.

CASE SUMMARY: The case is that of a 7y/o male presented with depressed sensorium and multiple cranial nerve deficits after 2 weeks of intermittent fever. Cranial computed tomogram and magnetic resonance imaging showed multiple parenchymal lesions involving the right frontal lobe, right side of the genu of the corpus callosum, left cerebellar hemisphere, left ventral pons, dorsal midbrain and right insula with volume loss. Eventually, he developed neutropenia. Bone marrow aspiration and CSF cytology showed hemophagocytosis and erythrophagocytosis, respectively, and was diagnosed with hemophagocytic Iymphohistiocytosis. He completed HLH-2004 chemotherapy protocol. Initial genetic studies showed a defect in syntaxin expression, indicating a familial type of HLH.

CONCLUSION: Hemophagocytic Lymphohistiocytosis is a life-threatening disease characterized by uncontrolled hyperinflammation on the basis of a variety of inherited or acquired immune deficiencies. Awareness of its clinical symptoms and diagnostic criteria is important to starting prompt life-saving therapy.