P20 A mysterious case of recurrent malignant melanoma

Abstract A 74-year-old White man presented to community dermatology services in 2020 with one lesion on the right temple and left forehead. These were investigated punch biopsies reported as benign intradermal melanocytic naevi. One year later, he was referred our teledermatology clinic a pink nodule temple, which had never healed following biopsy. The photos more keeping basal cell carcinoma (BCC) booked for an excision. Histology ulcerated invasive malignant melanoma (Breslow thickness 3.1 mm mitotic figures). At this stage, previous from reviewed (MM) confirmed. He and, skin examination, 7-mm BCC upper nasal bridge. We found small scar, but no lesions, temple. areas of psoriasis his elbows knees. No organomegaly or lymphadenopathy identified systemic examination. underwent wide local excision (WLE) MM scar sentinel lymph node neck, negative. Initial radiological imaging did not show any metastases. Three-month follow-up computed tomography showed colon thickening, patient diagnosed hepatic flexure tumour, treated hemicolectomy. Further evidence In September 2022, new 6-mm, light-brown indentation medial edge Initially, biopsy results recurrent melanoma. histological slide review immunochemical analysis demonstrated langerin multinucleated histiocyte-like infiltrates lymphohistiocytic inflammatory infiltrates; Langerhans histiocytosis (LCH) diagnosed. WLE positron emission tomography; we are still awaiting results. has been specialist haematology team is further management. LCH rare, multisystem haematological disorder clonal proliferation cells. Existing case reports document concomitant presentations myeloproliferative disorders, particularly myeloid leukaemias, noncutaneous manifestations, including pulmonary presentations. To best knowledge, there have presenting exclusively cutaneous manifestations clinically mimicking MM. rare incidence misleading presentation often its lack consideration differential diagnosis solitary lesions adults. This also highlights diagnostic challenges thorough investigation required unique condition.