Lymphohistiocytosis in the brain

In this issue of Neurology^®, Deiva et al.¹ describe the CNS features of primary hemophagocytic lymphohistiocytosis (HLH), a rare genetic immunodeficiency disorder associated with macrophage activation. Microcephaly, seizures, encephalopathy, abnormal spinal fluid (elevated protein, cellularity, or more specifically, hemophagocytosis), and periventricular white matter lesions characterize the CNS features of HLH, with progressive cognitive decline occurring in surviving, nontransplanted children. Of 46 children with HLH, 63% had abnormal neurologic examination, 50% had abnormal spinal fluid, and 33% had abnormal brain MRI.

Encephalopathy, multifocal neurologic deficits, and young age at onset renders challenging the distinction of HLH from acute disseminated encephalomyelitis (ADEM). Deiva et al. specifically compared the MRI features of the 46 children with HLH to those of 44 children with ADEM. Although both HLH and ADEM are characterized by bilateral, multifocal areas of increased T2 signal, the lesion distribution of HLH preferentially involved the periventricular white matter, and rarely involved the deep gray nuclei or brainstem. Although none of the MRI features were absolutely discriminatory, the relative involvement and symmetric nature …