P050 When ‘common becomes rare’: xanthosiderohistiocytic variant of xanthoma disseminatum in chronic myelomonocytic leukaemia

Abstract

Xanthoma disseminatum (XD) is a rare non-Langerhans-cell histiocytosis of unknown aetiology, characterized by reactive histiocytic proliferation with secondary lipid deposition, typically in patients who are normolipidaemic. Clinically, XD presents with yellow-to-brown papules/plaques and nodules, most commonly affecting the face, with potential involvement of flexural, truncal and intertriginous sites. Although the disease is predominantly cutaneous it may be associated with systemic involvement. Xanthosi­dero­histiocytosis (XSH) is regarded as a rare variant within the XD spectrum and has most frequently been reported in association with plasma-cell dyscrasias, with only a small number of cases described in the literature. We report a 64-year-old man with a background of chronic myelomonocytic leukaemia (CMML) who presented with a 5-year history of yellow-brown periorbital plaques, initially considered consistent with xanthelasma despite normal lipid studies. Three years later, he developed indurated plaques on both shins following recurrent episodes of presumed cellulitis, requiring multiple hospital admissions. During this period, he experienced significant unintentional weight loss without constitutional B symptoms. Persistence and intermittent inflammation of periorbital and lower-limb lesions prompted dermatological review and biopsy. Histopathological examination demonstrated dense dermal and subcutaneous infiltrates of foamy histiocytes and multinucleated giant cells with prominent haemosiderin deposition. The histiocytes were CD68+ and negative for CD1a, S100, SOX10 and melan-A, supporting a diagnosis of haemosiderotic xanthoma/xanthelasma within the spectrum of XSH. CMML had been diagnosed prior to the development of lower-limb lesions and had followed an indolent course. Magnetic resonance imaging of the orbits and positron emission tomography–­computed tomography demonstrated no extracutaneous involvement. The patient was commenced on doxycycline and topical clobetasol propionate, with no progression of cutaneous disease over 12 months of follow-up. This case highlights a rare xanthosiderohistiocytic variant within the XD spectrum occurring in association with CMML presenting as xanthelasma, and underscores the importance of clinicopathological correlation and multidisciplinary assessment in atypical xanthomatous eruptions.