155 A Unique Pediatric Case of Relapsing B- Acute Lymphoblastic Leukemia Presenting With Third-Degree Heart Block

Abstract

Despite the steady improvement in outlook for children with acute lymphoblastic leukemia (ALL), 20%-25% of patients still experience relapse. Isolated extramedullary relapse of acute leukemia is a rare occurrence. Most common sites for relapse are central nervous system and testes; however, unusual other sites have been reported. We report an unusual pediatric presentation of an extramedullary relapse of acute lymphoblastic leukemia. A 13-year-old boy with a known history of B acute lymphoblastic leukemia status post stem cell transplantation was referred to our hospital, complaining of cardiac arrest secondary to third-degree complete atrioventricular dissociation. He had undergone emergent implantation of transvenous pacing leads and had Breinholt myocardial biopsy. Microscopic examination of the myocardial biopsy revealed heavy infiltration of myocardium and pericardium by leukemic cells with focal fibrotic scar. Immunohistochemical staining of paraffin embedded tissue showed strong positivity of the leukemic cells for CD19, PAX5, CD79a, and CD10, and focal positivity for TdT, while CD3 was positive in few scattered T-cells. Epstein-Barr virus-encoded RNA (EBER) in situ hybridization was also performed and revealed a negative result. CT-guided bone marrow aspirate and core biopsy were performed and revealed no leukemic cells involving the bone marrow. A diagnosis of relapsing B acute lymphoblastic leukemia was rendered. Leukemic relapses are more devastating to patients and families than the original diagnosis. Most cases of cardiac leukemic relapses were reported in postmortem examinations. However leukemic myocardial involvement at antemortem examination is a rare finding. Current therapy protocols for isolated extramedullary relapse use intensive re-induction systemic chemotherapy in addition to site-specific therapy. Although rare, the present case is noteworthy in highlighting the unusual pediatric third-degree heart block presentation of relapse B-acute lymphoblastic leukemia.