The new definition of SIDS differs from the older definition in two aspects. Firstly it eliminated the term that death was “unexplained by history” because it is now known that many risk factors predispose infants to SIDS and that most cases of SIDS have some underlying abnormality too. Secondly it warrants detailed examination of the scene of death and autopsy to diagnose SIDS, thus eliminating wrong diagnosis of instances of child abuse or inherited disorders as SIDS. Currently due to the misdiagnosis of deaths as SIDS a new term “sudden unexpected death in infancy” (SUDI) is used. Unexplained SUDI generally includes cases of SIDS and other deaths which cannot be explained due to incomplete information or uncertain situations. It is now known that a multitude of factors from genetics to modifiable environmental triggers influence the pathogenesis of SIDS and this knowledge has lead to the formulation of different recommendations for its prevention.
SIDS is the most common cause of post-neonatal death in the USA. Epidemiological studies show that the risk of SIDS is greater than one in every thousand live births (Getahun D) with greater incidence in African and Native Americans. Although it is still the leading cause of death in infants less than 1 year of age, there has been considerable decline in its incidence since the 1980’s. This is due to the numerous studies that have been conducted which identified risk factors and underlying abnormalities which predispose infants towards SIDS and the guidelines for child care formulated from them. A large cross-sectional study carried out in Europe also showed that boys are at more risk of SIDS than girls (odds ratio of 1.49) (Carpenter RG). Interestingly SIDS is also seen to be 15-20 times more likely to occur in child-care settings. (Stable prevalence but changing risk factors of Sudden Infant Death Syndrome in child care setting in 2001)) SIDS rate and sleep position from 1988–2003 (deaths per 1,000 live births). As the graph shows rates of death by SIDS(bar graph) has decreased considerably as the rate of sleeping supine(line graph) in infants has increased since 1992. AAP_Academy of Paediatrics, BTS_Back to Sleep. Sleep position source: National Institute of Child Health and Human Development Household Survey. SIDS rate source: National Centre for Health Statistics, Centres for Disease Control and Prevention. PATHOLOGENESIS AND RISK FACTORS As mentioned above SIDS is diagnosed upon the basis of exclusion and hence it is confirmed only after investigations and autopsy according to protocol. During such autopsies of suspected SIDS cases certain definite changes and abnormalities were noted in respiratory and other organs. In a study to find evidence of antecedent hypoxia in SIDS cases it was noted that nearly 66% of cases had similar changes, with identifiable tissue markers, e.g. vascular endothelial growth factor (VEGF) in cerebrospinal fluid, to those of chronic persisting low-grade asphyxia. In deaths caused by SIDS the mean concentration of vascular endothelial growth factor in the CSF was found to be 308 pg/dL in contrast to non-SIDS deaths in which it was 85 pg/dL. (Jones KL) Other respiratory changes included thoracic petechiae and pulmonary congestion with edema. Certain brainstem and autonomic irregularities were also noted in other studies some of which were; continued rise in dendritic spines and slow formation of synapses in medulla indicative