The Disappearance of Sudden Infant Death Syndrome: Has the Clock Turned Back?

Racial differences within subsets of Sudden Unexpected Infant Death (SUID) with an emphasis on asphyxia

OBJECTIVE

Sudden Unexpected Infant Deaths (SUID) is defined as a combination of Sudden Infant Death Syndrome (SIDS), Unknown Cause of Death (UCD) and Accidental Suffocation and Strangulation in Bed (ASSB). Overall rates from 2000 to 2015 have been trending down. Racial differences in occurrence are seen.

STUDY DESIGN AND SETTING

Using the CDC Wonder Database, the total rates of SUID and its subsets were examined.

RESULTS

Non-Caucasian infant death rates for the total SUID group, and the SIDS component, are trending downward significantly faster than for Caucasians. UCD trends in rates show an apparent small, non-significant, decline for non-Caucasians, and are unchanged for Caucasians. ASSB rates are trending upward slightly more rapidly (not significantly) for non-Caucasians than Caucasians.

CONCLUSION

The trend showing ASSB trending upward more in non-Caucasians than Caucasians may suggest: 1) A racial difference that certifiers are more willing to certify SIDS than ASSB in Caucasians, and/or 2) Certifiers are biased towards certifying more ASSB than SIDS in non-Caucasians, and/or 3) Asphyxia risks may be increasing more in non-Caucasian SUIDs. Option #1 would require educational efforts to recognize the asphyxia risks in Caucasians. Option #2 would require documentation of racial bias in infant death certification followed by efforts to reduce the bias. Option #3 would require focused targeting of non-Caucasian populations to reduce asphyxia risks. Potentially all three scenarios could co-exist.

Sudden Unexpected Death in Neonates: A Clinico-pathological Study

Clinico-pathological studies that focus on sudden unexpected death (SUD) in the neonatal period are rare. The objective of this study was to elucidate the frequency and pathological spectrum of anatomical causes of death (CODs), found in the setting of sudden unexpected death in neonates (SUD-N), and to correlate the COD with premortem circumstantial information. We conducted a detailed review of all autopsy reports on SUD-N cases at our institution from 1997 to 2015. Analyzed clinical data included obstetrical history, postpartum/neonatal medical course, and circumstances surrounding death. Evaluated autopsy data included growth parameters, pathological findings, ancillary test results, and COD. Data from decedents in which a COD was established (COD-E) were statistically compared with that from decedents in which the COD was undetermined (COD-U). Of 104 neonates (M: 49; F: 55) who fulfilled our inclusion criteria, a COD was established at autopsy in 46 cases (44%). Infections, congenital abnormalities, and inborn errors of metabolism were the most common CODs. Single variables statistically more likely to be found in COD-E neonates were clinical history of prodromal illness, witnessed loss of vital signs, and evidence of physiological stress in the thymus or the liver. A prodrome was statistically more common in the COD-E group, but the absence of a prodrome does not reliably exclude COD-E cases, since over 50% of these patients were asymptomatic prior to their demise. In COD-U neonates, the statistically significant factors were death during sleep, death during sleep while "bed"-sharing, "heavy" lungs, and petechial hemorrhages on the epicardium or pleura. Given the frequency and wide spectrum of underlying pathologies in COD-E neonates, referral of SUD-N cases to pathologists with specialized pediatric autopsy expertise is recommended.

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.

An Approach to the Classification of Apparent Asphyxial Infant Deaths

Recent evidence indicates that with thorough, high quality death investigations and autopsies, forensic pathologists have recognized that many unexpected infant deaths are, in fact, asphyxial in nature. With this recognition has come a commensurate decrease in, and in some cases, abolition of, the label "sudden infant death syndrome" (SIDS). Current controversies often pertain to how and why some infant deaths are determined to be asphyxial in nature and whether or not apparent asphyxial circumstances are risk factors for SIDS, or rather, harbingers of asphyxial deaths. In an effort to sidestep these controversies, some forensic pathologists elected to instead use the noncommittal label "sudden unexpected infant death" (SUID), leading to the unfortunate consequence of SUID - like SIDS - gaining notoriety as an actual disease that could be diagnosed, studied, and ultimately cured. Although it is not possible to provide death certification guidance for every conceivable type of unexpected infant death, we recognize and propose a simple classification system for overarching themes that cover the vast majority of cases where infants die suddenly and unexpectedly.