Erdheim-Chester disease: A multisystem non-Langerhans cell histiocytosis with cutaneous involvement.

Erdheim-Chester disease (ECD) is a rare non-Langerhans cell histiocytosis (LCH) marked by systemic involvement and diverse clinical manifestations. We report a 35-year-old man with yellowish-brown periorbital lesions initially diagnosed as xanthelasma, which later recurred. The patient developed neurological symptoms, including proximal lower limb weakness and cranial nerve palsies, which improved with corticosteroids. Imaging revealed retro-orbital masses, pan-rhinosinusitis and extensive sclerosis of the sinonasal cavity, along with systemic organ involvement, including the kidneys and spine. Histopathology demonstrated foamy histiocyte infiltration, positive for CD163 and CD68 but negative for S100. The BRAF V600E (B-raf proto-oncogene valine-to-glutamic acid substitution at position 600) mutation was absent. A multidisciplinary team initiated the LCH III protocol, leading to partial regression of cutaneous lesions and stabilisation of neurological symptoms. This case highlights the importance of recognising atypical ECD presentations and suggests the LCH III protocol may benefit BRAF-negative cases. Multidisciplinary management is critical given the disease's progressive, multisystem nature.