A 20-MONTH-OLD mixed-race male toddler, who had been entirely well, was found unresponsive by his mother one morning. Resuscitation by paramedics and emergency department personnel was unsuccessful. An appointment with a private physician for that day had been cancelled because a mild upper respiratory tract infection had resolved.
Significant autopsy findings were confined to the heart, which weighed 53 g (expected, 56 g). The myocardium was slightly pale, but no focal lesions were discernible, even by dissecting microscopy (Figure 1). The left ventricular free wall was 0.9 cm, interventricular septum was 0.8 cm, and right ventricular free wall was 0.2 to 0.3 cm. Light microscopy revealed multiple, small, well-demarcated aggregates of apparently altered cardiac myocytes or Purkinje's cells (Figure 2). Affected cells were polygonal, with abundant granular eosinophilic cytoplasm and few or no myofibers (Figure 3). Occasional individual cells were only partly altered. There was a pronounced predilection for the