A Fresh Look at the History of SIDS

Sudden infant death syndrome (SIDS) became a named entity in 1969 and the term has been used to certify sudden unexpected infant deaths meeting certain demographic, epidemiologic, and pathologic criteria. Since it is a diagnosis of exclusion, there is inherent imprecision, and this has led the National Association of Medical Examiners to recommend that these deaths now be classified as "undetermined." This historical review article briefly analyzes anecdotal instances of SIDS described centuries ago as overlying, smothering, infanticide, and suffocation by bedclothes followed by a more detailed review of "thymic" causes (i.e., thymic asthma and status thymicolymphaticus) popular in the late 1800s and early 1900s. Before the 1950s, such cases were also often categorized as accidental mechanical suffocation. In the 1940s and 1950s, forensic studies on infants dying unexpectedly revealed a typical pattern of autopsy findings strongly suggestive of natural causation and, after 1969, cases meeting the appropriate criteria were usually categorized as SIDS, a term embraced by the public and by advocacy groups. Research conducted after the 1960s identified important risk factors and generated many theories related to pathogenesis, such as prolonged sleep apnea. The incidence of SIDS deaths decreased sharply in the early 1990s after implementing public awareness programs addressing risk factors such as prone sleeping position and exposure to smoking. Deletion of cases in which death scene investigation suggested asphyxiation and cases where molecular autopsies revealed metabolic diseases further decreased the incidence. This historical essay lays the foundation for debate on the future of the SIDS entity.