Myeloid sarcoma of the heart: Extramedullary relapse of acute myeloblastic leukemia, presenting with complete heart block and atrial flutter after second allogeneic stem cell transplantation.

We report isolated extramedullary relapse in a 14-year-old boy, sequentially presenting with intestinal and cardiac myeloid sarcoma (MS). Acute myeloblastic leukemia M5 was diagnosed 41 months ago. On the 14th month of the second HSCT, he presented with ileus and underwent surgical treatment. After 2 weeks, arrhythmia, bradycardia, complete heart block, and atrial flutter developed and echocardiography revealed multiple cardiac masses. There was no bone marrow relapse but pathology of the intestinal biopsy showed leukemic infiltration. Patient was successfully treated with a permanent pacemaker and salvage chemotherapy. To the best of our knowledge, this is the first pediatric cardiac MS developed after HSCT.