Biochemical, cytological and histopathological examination of sudden unexpected death in infancy.

To evaluate the pathophysiological mechanisms underlying sudden infant death syndrome (SIDS), four sudden unexpected death in infancy (SUDI) and four sudden deaths in children over 1 year of age were examined. In the SUDI cases, increased numbers of scavenger receptor A positive (SRA(+) ) cells (4/4), numerous platelet aggregates (3/4), and tumor necrosis factor (TNF)-α(+) cells (4/4) were observed in the peripheral blood (PB) smear preparations. Macrophage colony stimulating factor, interleukin (IL)-6, IL-8, TNF-α and IL-1β all exceeded the normal levels. Minute foci of inflammatory lung injury (4/4), numerous platelet emboli in lungs and among cardiac myocytes (3/4) and appreciable contraction band necrosis (1/4) were observed. And neutrophils accumulated in the capillaries of injured organs and endothelial cells were extensively injured. From these findings, cytokine abnormality induced by SRA(+) cells in PB was considered to play an important role in the development of tissue injury, and platelet emboli or contraction band necrosis might have been the leading cause of death in our SUDI cases. Patients with characteristics thought to be similar to our SUDI cases were included in the SIDS group; cytokine abnormality was considered to be one of the underlying mechanisms in SIDS.