BRAF mutation in overlapping forms of Erdheim-Chester and Rosai-Dorfman diseases: A unique case restricted to the central nervous system

A 48-year-old man with a history of pleural tuberculosis presented in 2019 with paraesthesia of the left hemiface. The clinical examination was consistent with a fifth cranial nerve involvement. A brain MRI revealed three hyper-FLAIR and contrast enhanced lesions in the left cerebellar peduncle (Fig. 1), the left temporal lobe and the left occipital lobe. Perfusion images showed no hyperperfusion, and spectroscopy revealed a tumour profile, with a pick of choline and low NAA. A whole-body CT scan, PET CT scan, spinal MRI, CSF analysis and blood tests were normal, leading to the conclusion of an isolated brain disease. Therefore, a biopsy of the left temporal lesion was performed to differentiate the three main diagnostic hypotheses: infectious (tuberculosis); inflammatory (neurosarcoïdosis, neuro-Behcet); tumoral (primary CNS lymphoma) disease.