Monoclonal Gammopathy of Multisystemic Significance: A Challenging Diagnosis of Light Chain Amyloidosis.

We present a case of a 51-year-old woman diagnosed with light chain amyloidosis associated with monoclonal gammopathy of undetermined significance (MGUS). Initially, she presented with symptoms of heart failure, including palpitations, chest tightness, and shortness of breath, which were attributed to myocarditis based on cardiac magnetic resonance (CMR) imaging findings. However, her condition rapidly deteriorated, with recurrent admissions for worsening heart failure, cardiogenic shock, and stroke. A cardiac biopsy ultimately confirmed light chain amyloidosis, a rare complication of MGUS, which has a long-term risk of 0.8% in patients with light chain MGUS. Despite aggressive treatment, including chemotherapy and biventricular assist device implantation, her condition continued to decline, and she became ventilator-dependent and subsequently passed away. This case highlights the importance of considering amyloidosis in patients with MGUS and underscores the need for early diagnosis and intervention to prevent catastrophic outcomes.