Sporadic Late-Onset Nemaline Myopathy with Cardiomyopathy Presenting as Advanced Heart Failure Despite Autologous Stem Cell Transplantation: A Case Report

Background Nemaline myopathy is a rare neuromuscular disorder characterized by severe muscle weakness and dyskinesia, predominantly affecting skeletal muscles. Notably, significant cardiac involvement, especially in the sporadic late-onset subtype, is exceptionally uncommon. Case Summary A 31-year-old female patient presented to our hospital with a six-month history of chest tightness and progressive peripheral edema for ten days, superimposed on a two-year course of proximal muscle weakness. Four months prior, she received a diagnosis of sporadic late-onset nemaline myopathy complicated by monoclonal gammopathy of uncertain significance, followed by autologous stem cell transplantation two months ago. The patient presented with advanced heart failure, characterized by dilated cardiac chambers and impaired ventricular systolic function, as evidenced by an echocardiographically derived left ventricular ejection fraction of 25%, an elevated pro-brain natriuretic peptide of 4,673 pg/mL, and polyserosal effusions. Extensive late gadolinium enhancement in the ventricular walls on cardiac magnetic resonance imaging confirmed the suspected diagnosis of heart failure secondary to sporadic late-onset nemaline myopathy-related cardiomyopathy. Following active treatment with guideline-directed medical therapy for heart failure, the patient was discharged in an improved clinical condition, with her left ventricular ejection fraction increasing to 57% at the six-month follow-up. Discussion This case report highlights that sporadic late-onset nemaline myopathy may progress to severe cardiomyopathy and even heart failure, notwithstanding autologous stem cell support. Current evidence supports the application of standard heart failure medications as a rational therapeutic strategy.