Severe obstructive hypertrophic cardiomyopathy occurring secondary to mitochondrial disease.

Mitochondrial disorders have been recognized as important secondary causes of cardiomyopathies. Differentiation of these cases from primary cardiomyopathies is important since the pathogenesis, accompanying systemic manifestations, and prognosis may be different. The typical cardiac manifestation of mitochondrial disorders is hypertrophic cardiomyopathy. We report on an 11-year-old girl with severe obstructive hypertrophic cardiomyopathy and mild myopathy of the lower extremities. Surgical left ventricular septal myectomy was performed and ragged red fibers typical of mitochondrial disorders were detected on histological examination of the resected myocardial sample. Subsequent electron microscopic examination revealed ultrastructurally abnormal mitochondria in the skeletal muscle biopsy, though respiratory chain enzyme analysis was normal. Cardiomyopathy may be the presenting or the sole manifestation of a mitochondrial disorder. Nonobstructive hypertrophic cardiomyopathy has been considered to be the typical cardiac phenotype of mitochondrial disorders, and cases with left ventricular outflow tract obstruction have only rarely been reported.