[Neuro-Langerhans cell histiocytosis]

Langerhans cell histiocytosis (LCH) is a rare multisystemic disease. LCH is characterized by proliferation of myeloid progenitors with altered differentiation program and similar phenotypic features to epidermal dendritic cells termed Langerhans cell. LCH cells express CD1a+ and langerin and exhibit BRAF V600E mutation in ∼50% of cases. Neurological involvement or neuro-LCH is observed in 5 to 10% of cases. Three subtypes of neuro-LCH are individualized. The tumor type, accounting for 45% of neuro-LCH, affect mainly young adults. Tumor neuro-LCH is characterized by space occupying lesion(s) with contrast enhancement on MRI. Clinical symptoms are due to tumor brain location(s). Pathological examination of tumor neuro-LCH lesions reveals typical features of LCH. Treatment relies on surgical resection with/without chemotherapy. Degenerative neuro-LCH, accounting for 45% of cases, is usually revealed, mostly in children, by: (i) a cerebellar syndrome, (ii) a pyramidal syndrome, (iii) a pseubulbar palsy, and/or (iv) cognitive disorders. On MRI, several signs may coexist: (i) cortex atrophy, (ii) white matter T2 hyperintensities, and (iii) deep gray matter T1 hyperintensities. Pathological analysis of degenerative neuro-LCH lesions have been rarely performed and have never detected CD1a+ histiocytes but unspecific lesions (i.e. gliosis, neuronal loss and/or demyelination). Treatment of degenerative neuro-LCH patients is poorly standardized and poorly efficient. Functional rehabilitation and socio-educational care of these young patients are crucial. The mixed subtype of neuro-LCH combines clinico-radio-pathological characteristics of the first two first forms in the same patient, and represents 10% of neuro-HL. Neuro-HL, therefore, includes three very distinct entities with epidemiological, clinical, radiological and histological specific features requiring specific medical management.