Light chain deposition disease (LCDD) also known as nonamyloidotic immunoglobulin deposition disease is a rare systemic disorder due to the abnormal deposition of immunoglobulin in multiple organs caused by the clonal proliferation of B lymphocytes and plasma cells. Renal involvement is the most common with cardiac manifestations being the most common extra renal presentation of the disease. Renal involvement is not always associated with LCDD. Isolated cardiac involvement can manifest in a wide variety of ways: heart failure, cardiomyopathy, arrhythmias, angina, myocardial infarction, etc. We hereby present an unusual case of 59-year-old female who presented to clinic for routine follow up. A murmur on physical exam was evaluated with echocardiogram which led to the discovery of an incidental right atrial mass. Cardiac magnetic resonance imaging was completed 6 months later for follow up which showed increasing size of the mass. The mass was excised and found to be consistent with LCDD. To the best of our knowledge, this is the first reported case of LCDD manifesting as an atrial mass.

Through this case report and review of literature we would like to generate awareness among our fellow pathologists and clinicians to maintain a high level of suspicion for LCDD as it can manifest in many unusual ways, with or without kidney involvement.

轻链沉积病（LCDD）又称非淀粉样免疫球蛋白沉积病，是一种罕见的全身性疾病，是由于B淋巴细胞和浆细胞克隆性增殖引起免疫球蛋白在多器官异常沉积所致。肾脏受累是最常见的，心脏表现是该疾病最常见的肾外表现。肾脏受累并不总是与 LCDD 相关。孤立的心脏受累可以通过多种方式表现出来：心力衰竭、心肌病、心律失常、心绞痛、心肌梗塞等。我们在此介绍一个不寻常的 59 岁女性病例，她到诊所进行常规随访。用超声心动图评估体检时的杂音，导致偶然发现右心房肿块。6 个月后完成心脏磁共振成像进行随访，结果显示肿块越来越大。肿块被切除并发现与 LCDD 一致。据我们所知，这是第一个报告的 LCDD 表现为心房肿块的病例。

通过本病例报告和文献回顾，我们希望提高我们的病理学家和临床医生同行的意识，以保持对 LCDD 的高度怀疑，因为它可以以许多不寻常的方式表现出来，有或没有肾脏受累。