Histopathological observation of the heart with diffuse and abnormal proliferation of mitochondria in myocardial cells (mitochondrial cardiomyopathy): report of an adult case.

An autopsy case of idiopathic dilated cardiomyopathy with abnormal proliferation of mitochondria in the myocardial cells is reported. The case is that of a 39-year-old male with congestive heart failure. The heart was 700 g and showed marked dilatation of all cardiac chambers with myocardial fibrosis of the left ventricular myocardium and interventricular septum, especially in the basal portion of the left ventricular posterior wall. Myocardial cells were hypertrophied with a marked increase of fine-granular sarcoplasm, containing numerous mitochondria, seen by electron microscopy. The mitochondria were usually round or oval and ranged in size from 0.3 to 1.2 micron in diameter. The cristae of these mitochondria frequently showed a concentric lamellar or reticular configuration. Myofibrils were unusually scarce, but the sarcomere structure and arrangement of myofilaments were well-preserved. Epicardial and intramural coronary vessels were almost normal. From these findings, we consider this to be an adult case of mitochondrial cardiomyopathy.