DP20 Necrobiotic santhogranuloma of the scalp with nonprogressive thrombocytopenia: a case report
Authors: Kemp Alexandra , Johnson Peter 
Published: June 2023

Abstract
We present the case of an 84-year-old woman referred with a 6-month history of a lesion on her occipital scalp. Examination revealed a creamy-white, nonscaly nodule measuring 15 × 15 mm with surface telangiectasia. Her past medical history included basal cell carcinoma, stage 3 kidney disease, cardiovascular disease and osteoporosis. A diagnosis of necrobiotic xanthogranuloma (NXG) was confirmed on incisional biopsy, and the patient went on to have full excision. Given the association with haematological malignancies, and following discussion with our local haematologist, investigations included full blood count, bone profile, immunoglobulins, serum and urinary protein electrophoresis and serum free light chains. This revealed a low platelet count of 108 × 109 cells L–1 (reference interval 150–450) but no other significant abnormalities. Our local haematologist considered a bone marrow biopsy, but after discussion with the patient, this was declined. Necrobiotic xanthogranuloma is a rare non-Langerhans histiocytosis. It classically presents as a yellow, red or purplish papule or nodule in the periorbital region, so this case had an unusual site. The mean age of onset is in the sixth decade of life, with an equal sex distribution. Pathogenesis is unknown. Necrobiotic xanthogranuloma is associated with haematological malignancies, particularly paraproteinaemia and lymphoproliferative disease. Differential diagnoses include xanthelasma, chronic lupus erythematosus, sarcoidosis and necrobiosis lipoidica. Where lesions become infiltrative and plaque-like, mycosis fungoides and psoriasis can also be considered. Given the relatively rare nature of NXG, there is no consensus for optimal treatment. In localized skin lesions such as in our patient, surgical excision is often undertaken. Other reported treatments are directed at the associated paraproteinaemia and include chlorambucil and small-dose corticosteroids, cyclophosphamide, melphalan, azathioprine, thalidomide, interferon-α and intravenous immunoglobulin. Classical features on histology include palisading xanthogranulomas with foci of necrobiosis in the mid-dermis and diffuse granulomatous panniculitis with foreign body-type reaction and Touton giant cells. Our histology slides showed a relatively atrophic epidermis with a dense dermal and subcutaneous infiltrate consisting of lymphocytes, foamy macrophages, plasma cells and Touton-type multinucleate giant cells with areas of necrobiosis. There were also reactive lymphoid follicles with germinal centres. Given the association with internal malignancy, it is important to diagnose these lesions correctly. To date, our patient has not developed any haematological malignancy, although is at increased risk in the future and has been counselled and monitored accordingly. It remains unclear whether the presence of thrombocytopenia alongside NXG is a coincidental finding or marker for future lymphoproliferative disease, as there are no other published case reports of such an association.