Extramedullary intracardiac multiple myeloma misdiagnosed as a thrombus: a case report.

Background: Extramedullary intracardiac multiple myeloma (MM) is extremely rare. Patients with extramedullary intracardiac MM may suffer from a poor prognosis. Experience in the diagnosis and therapy of cardiac involvement in MM is limited. Herein, we describe a 67-year-old male with extramedullary intracardiac MM who was initially misdiagnosed with a thrombus.

Case Presentation: A 67-year-old male was admitted for exertional dyspnea and fatigue. The patient was diagnosed with MM one year earlier and had complete remission after chemotherapy. He was implanted with a permanent pacemaker two months prior due to sick sinus syndrome. After this admission, transthoracic echocardiography (TTE) and computed tomography (CT) confirmed the existence of a large right atrial mass extending to the superior and inferior vena cava. We initially considered the right atrial mass as a thrombus and performed surgical treatment for the patient. The surgical intervention partially relieved the obstruction of the superior and inferior vena cava and improved hemodynamics. Postoperative pathological examination of the right atrial mass suggested malignant plasmacytoma associated with MM. After recovery from the surgery, the patient received one cycle of chemotherapy. A follow-up of seven months revealed that our patient was still alive with a good general condition.

Conclusions: Increasing the awareness of extramedullary intracardiac lesions in patients with MM is warranted. Our case confirmed that surgical intervention followed by adjuvant chemotherapy could improve the patient's hemodynamics and achieve remission of cardiac symptoms.