= macrophage-related disorder characterized by excess lymphocytes + activated macrophages, typically with hemophagocytosis

Histo: absence of CD1a

Location: bone marrow, spleen, liver, lymph nodes

Classification:

1. primary / familial autosomal recessive form (~ 25%) in infants
2. secondary form in older children + adults

Associated with: infection, prolonged immunosuppression

• serum ferritin levels >10,000 µg/L (90% sensitive, 96% specific)
• seizures, altered consciousness, hemiparesis, ataxia
• nuchal rigidity

Chest X-ray:

• interstitial opacities ± pleural effusion

MR:

• subcortical white matter foci with ↑ T2 signal intensity
  Location: frontal + parietal lobes, basal ganglia
• leptomeningeal enhancement
• cerebral volume loss → dilated ventricles + prominent extra-axial fluid

CT:

• calcifications favoring gray-white matter junction
• hepatosplenomegaly

US:

• gallbladder wall thickening, ↑ periportal echogenicity
• ascites, lymphadenopathy
• nephromegaly, ↑ renal cortical echogenicity

Dx: at least 5 of 8 criteria: (1) fever (2) splenomegaly (3) cytopenia of at least two cell lineages (4) hypertriglyceridemia ± hyperfibrinogenemia (5) tissue hemophagocytosis (6) low and/or absent natural killer cell activity (7) hyperferritinemia (8) high-soluble interleukin-2 receptor levels

Prognosis: variably relapsing + remitting / rapidly progressive; fatal if untreated