A commentary on changing infant death rates and a plea to use sudden infant death syndrome as a cause of death.

In his editorial entitled Changing Infant Death Rates— Diagnostic Shift, Success Story, Or Both, Byard concludes that changes in rates away from sudden infant death syndrome (SIDS) towards another cause of death (COD) are appropriate [1]. Improved death scene investigations and autopsies leading to increased awareness of potential dangers imposed by infant sleep sites have been instrumental to the diagnostic shift occurring in cases of sudden unexpected infant death. Given abundant supportive data accumulating over the past few years, we certainly agree. But where do we go from here in order to bring about greater consensus and accuracy in establishing CODs in these cases? Over the past four decades, the original definition of SIDS [2] has undergone several refinements focusing principally on mandating death scene investigations, circumstances of death, association with sleep, and certainty of the COD [3–5]. Yet, each subsequent iteration has remained exclusionary with respect to the COD and is encumbered with its own diagnostic dilemmas given the lack of a pathognomonic postmortem marker, incomplete death scene investigations, and limited postmortem examinations and ancillary testing as well as philosophical differences with and objections to the concept of SIDS itself among death certifiers [6]. As a result, other labels including sudden unexpected death in infancy (SUDI), sudden unexpected infant death (SUID), unclassified sudden infant death (USID), Undetermined, and Unascertained, have gained wider currency in an ever increasing proportion of these challenging cases. The choice between SIDS and these latter COD certifications now often centers on death scene findings that suggest an asphyxial risk to the sleeping infant. However, present investigative methods neither precisely quantify nor determine the certainty of its lethality in the absence of reliable postmortem evidence of its significance; hence the slippery slope of COD assignment. The present uncertainty in analyzing the circumstances of death in these cases is demonstrated in our recent study wherein five pathologists blinded to one another and using a classification scheme focused on the estimated risk of asphyxia at the death scene as described in the investigative reports assigned a COD to 117 sudden infant death cases including 83 cases with SIDS as the original COD [7]. The reviewers concluded that the death scene contributed to or actually caused death in 32–50 % of the entire case study group and in 40–59 % of the 83 SIDS cases. Among the 83 original SIDS cases, SIDS as the COD decreased by 55–69 % and another COD was considered plausible in 2–12 % of the cases. Although SIDS remains an exclusionary COD, its underlying elements and the mechanism of death as hypothesized in the triple risk hypothesis are being unraveled [8]. According to this hypothesis, ‘‘SIDS, or an important subset of SIDS, is due to abnormal brainstem mechanisms in the control of respiration, chemosensitivity, autonomic regulation, and/or arousal which impairs the infant’s response to life-threatening, but often occurring, stressors during sleep (e.g., hypoxia, hypercarbia, asphyxia, hyperthermia) and leads to sudden death in a vulnerable developmental period’’ [9]. Thus, according to this hypothesis, SIDS infants who are intrinsically vulnerable as a result of underlying pathology must be exposed simultaneously to risk factors, such as prone sleep position, during their physiologically unstable stage of development during sleep, before they will succumb. This period of H. F. Krous (&) Department of Pathology, Rady Children’s Hospital, 3020 Children’s Way, M5007, San Diego, CA 92123, USA e-mail: hkrous@rchsd.org