Pathology of the Liver in Familial Hemophagocytic Lymphohistiocytosis

Familial hemophagocytic lymphohistiocytosis is a rare, rapidly progressive disorder characterized by an activation of the immune system resulting in a systemic proliferation of lymphocytes and histiocytes. The disease is genetically heterogeneous and maps to at least 4 loci including the gene encoding perforin, a protein critical for the cytotoxic and regulatory functions of T lymphocytes and natural killer (NK) cells. Hepatic dysfunction often occurs early in the clinical course, but the pathology of the liver is not well characterized. The clinical history, laboratory data, and pathologic material (25 hepatic specimens) from 19 children (11 boys, 7 girls, 1 unknown, 12 d to 11mo of age, median 3 mo) with FHL were reviewed. Routine and immunohistochemical stains were carried out in all cases, and perforin gene sequencing in a subset. Common to all specimens was a portal and sinusoidal infiltrate of CD3(+), CD8(+), granzyme B+ lymphocytes admixed with CD68(+), CD1a- histiocytes that exhibited hemophagocytosis. There was endothelialitis of portal and central veins and lymphocyte-mediated bile duct injury. The degree of portal and sinusoidal lymphohistiocytic infiltrate and endothelialitis varied from mild to marked and correlated with clinical severity. In some specimens, histiocytic cells predominated and in others, there was extensive hepatocellular giant cell transformation. Accordingly, 4 histopathologic patterns were observed: (1) chronic hepatitis-like, (2) leukemia-like, (3) histiocytic storage disorder-like, and (4) neonatal giant cell hepatitis-like. Two siblings homozygous for a 50delT nucleotide deletion had no perforin immunoreactive cells, 1 compound heterozygote for a deletion and missense mutation had cells with markedly diminished perforin expression, and 1 infant hemizygous for a perforin missense mutation had intact expression. Recognizing the morphologic changes in the liver and the immunophenotypic features of the infiltrate are critical for a rapid diagnosis and a prompt institution of treatment.