Autologous stem cell transplantation in multiple myeloma with SCN5A overlap channelopathy: a structured arrhythmic risk-mitigation strategy

Autologous stem cell transplantation (ASCT) is a cornerstone of therapy for transplant-eligible multiple myeloma (MM), but its use in patients with inherited arrhythmic disorders such as SCN5A-related channelopathies remains challenging, and evidence to guide management is limited.We report the case of a 64-year-old woman diagnosed with MM and a germline SCN5A mutation associated with an overlap phenotype of Long QT and Brugada syndromes. Following multidisciplinary evaluation, ASCT was pursued. After daratumumab-based induction therapy, achieving a very good partial response, stem cell mobilization was performed using granulocyte colony-stimulating factor alone. ASCT with high-dose melphalan was carried out under a structured, protocol-driven risk mitigation strategy, including continuous electrocardiographic monitoring, strict electrolyte management, careful selection of non-QT-prolonging drugs, and procedural adaptations such as stem cell wash. No arrhythmic events occurred, treatment-related toxicities were successfully managed, and hematologic recovery was achieved as expected. This case highlights that ASCT is feasible and can be safely performed in MM patients with SCN5A-related channelopathies using a multidisciplinary, individualized risk mitigation approach, challenging the concept of absolute contraindication.