Mitochondrial cardiomyopathy with involvement of skeletal muscles.

In this report we describe an idiopathic hypertrophic cardiomyopathy in a 21 month old infant girl; who died shortly after a small surgical intervention for cardiovascular failure. Fine structural investigation disclosed an extreme increase of often abnormally structured and enlarged mitochondria and a great loss of myofibrils in the heart muscle cells. Furthermore, mitochondrial hyperplasia was observed focally in all skeletal muscles investigated. The pathogenesis of this mitochondriopathy in heart and skeletal muscle is unknown. It might be a consequence of a functional mitochondrial defect with compensatory hyperplasia of mitochondria. Differential diagnosis of this very rare infantile cardiomyopathy from the myopathies of storage diseases, typical hypertrophic cardiomyopathy and carnitine defiency is discussed, as is the distinction from the oncocytic or so-called histiocytic transformation of heart muscle cells. Methological hints for diagnostic procedures are given.