Central nervous system-predominant Erdheim–Chester disease mimicking meningioma responding to BRAF inhibitor therapy: the importance of molecular diagnosis and targeted therapy in rare neoplastic disorders

Erdheim–Chester disease (ECD) is a rare multi-system, non-Langerhans cell histiocytic disorder (NLCHD) with only a few hundred cases reported in the literature. Its diverse clinical manifestations require a high level of diagnostic suspicion. BRAFV600E mutation analysis is of critical significance, as it has implications for targeted therapy with BRAF inhibitors such as vemurafenib and dabrafenib. We report a case of symptomatic, central nervous system (CNS)-predominant ECD initially presenting with CNS mass lesions mimicking meningiomas on imaging and prominent periorbital xanthogranulomas. CNS presentation of ECD, although not infrequent, bears particular significance here from a therapeutic point of view, since only partial debulking was possible owing to anatomical complexities. Radiological evaluation following surgery showed no significant change in the size of the lesions. Targeted therapy was commenced following histopathology, immunohistochemistry (IHC), and molecular testing, resulting in marked improvement of clinical symptoms and tumor regression. Thus, diagnostic accuracy was imperative for symptomatic relief in this rare but aggressive neoplasm with a complex clinical presentation and misleading initial radiological impressions, bearing an otherwise grim prognosis.