P20 A mysterious case of recurrent malignant melanoma

Abstract

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