Infantile cardiomyopathy with histiocytoid change in cardiac muscle cells. Report of six patients.

Clinical and pathologic findings are presented in 14 patients (six newly reported, eight described previously), all children ranging in age from 6 to 24 months, with a clinicopathologic syndrome termed "infantile cardiomyopathy with histiocytoid change in cardiac muscle cells." This syndrome is manifested clinically by severe, eventually fatal cardiac arrhythmias, and is characterized pathologically by cardiac hypertrophy and by a distinctive type of focal degeneration of the muscle cells, which lose their myofibrils, undergo marked mitochondrial hyperplasia, become rounded in shape and enlarged, and resemble histiocytes. Evidence is presented to support the conclusions that these manifestations are those of a cardiomyopathy, that cardiac hypertrophy precedes the onset of the clinical features, that the focal degeneration is likely to be a cause rather than a consequence of the arrhythmias, and that the latter develop only in the late stages of the disorder. The etiology of this cardiomyopathy remains unclear.