Leukaemia cutis as a late, isolated extramedullary relapse: a case report of a patient with acute myeloid leukaemia 6 years after allogeneic bone marrow transplantation and remission.

Leukaemia cutis (LC) is characterized by the infiltration of leukaemic cells into skin tissue, presenting as various skin lesions. It can signal relapse or coexist with extramedullary or systemic relapses. Extramedullary relapse, particularly in sanctuary sites like the skin, remains a clinical challenge, demanding investigation into mechanisms and monitoring strategies. We present a unique case of isolated extramedullary relapse manifesting as LC, 6 years after successful allogeneic bone marrow transplantation for acute myeloid leukaemia. A 24-year-old man exhibited a cutaneous nodule on his scalp, prompting comprehensive evaluation. Despite achieving complete remission post-transplantation, a core needle biopsy confirmed LC. Extensive assessments, including blood tests and bone marrow biopsy, returned normal results. As the disease was confined to skin, the patient received local radiotherapy. This case instead highlights the overall challenge of detecting and treating late, isolated extramedullary relapse.