Haemophagocytic lymphohistiocytosis restricted to the central nervous system.

An 8-year-old boy presented with fatigue, weakness and altered mental status necessitating intubation. Contrast-enhanced magnetic resonance imaging (MRI) of the brain revealed multifocal perivascular enhancement at the supratentorial juxtacortical white matter (figure 1A) and diffuse cerebellar leptomeningeal enhancement (figure 1B), suggestive of central nervous system (CNS) vasculitis versus infection versus acute disseminated encephalomyelitis (ADEM). Workup for infectious and autoimmune encephalitis was unremarkable. Methylprednisolone (20 mg/kg/day) was initiated for presumed ADEM. Brain biopsy, obtained due to continued deterioration in mental status, revealed extensive meningoencephalitis (figure 2A) and …