A case of extramedullary hematopoiesis presenting as hemorrhagic panniculitis and evolving in acute myeloid leukemia.

Extramedullary hematopoiesis (EMH) in adults is a rare event, usually associated with myeloid disorders, and can be the first sign of chronic myelomonocytic leukemia. We report a case of EMH presenting as a hemorrhagic panniculitis in a patient who did not apparently present any myeloid disorders. The patient received previous chemotherapy for mantle cell lymphoma localized to the large bowel and had been in complete remission for 3 years. The diagnosis of EMH was achieved after a deep incisional biopsy of a nodule from the thigh, and with pathological examination that included immunohistochemical studies. After a follow-up of 14 months, the patient developed an acute myeloid leukemia, classified as therapy-related myeloid neoplasm, according to the 2016 World Health Organization (WHO) classification of hematological malignancies. As shown by the rare cases described in literature, the presence of cutaneous EMH should always be a trigger for investigating the patient's hematological system; also, in our experience, a long follow-up is mandatory.