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A commentary on the review by Goldwater
If scientific research of Sudden Infant Death Syndrome (SIDS) is to be judged on how well it now understands this syndrome after four decades of intensive research it has been a spectacular failure. If however, it is to be judged on the number of young lives saved, it has ultimately been a resounding success. Dr Goldwater’s critical insight in this issue1 into our lack of knowledge regarding the aetiology of SIDS and our slow uptake on fully using pathological clues to examine potential causal mechanisms are fully justified, but his observation that much research, effort, time, and money has been wasted is not.
To argue that the present rate of SIDS is returning back to similar levels observed in the 1970s and may be due to natural variation rather than the “back to sleep” campaign may seem feasible when looking at small data sets, but such variation would be on an epidemic scale in larger populations. This argument also ignores both the fall in all postneonatal deaths during this period and the strong negative correlation between the increase in infants placed supine to sleep with the decrease in SIDS. The low levels in the 1970s, as Mitchell observed,2 were probably due to deaths previously labelled as respiratory conditions, slowly being relabelled to this new classification of SIDS. National data from England and Wales3 have since confirmed that there was indeed a diagnostic shift. This being the case, in England and Wales alone, nearly 10 000 lives have been saved in the past decade, which is a testament to all who work in the SIDS field.
The reduction has been brought about through epidemiological observation rather than any clinical, pathological, or genetic insight, but the process has been one of working out the answers without really understanding the mechanism of risk. Repeated population studies pointed to the prone position, and successful intervention campaigns have shown beyond doubt this position is part of the causal pathway for some of the deaths, but we have little idea as to what this pathway is. Nevertheless this approach of identifying potential factors and using frequency comparison in a multivariate setting can lend itself to other disciplines. Dr Goldwater has identified certain pathological markers of SIDS which in themselves may be non-specific and considered inadequate to represent a cause of death. These include liquid blood found in the heart of SIDS infants, the size number and distribution of intrathoracic petechial haemorrhages, fluid laden heavy organs, inflammation of the trachea and bronchioles, and bacterial toxins potentiated with viral infection and/or exposure to tobacco smoke. However, used in combination with each other and epidemiological findings may be predictive of certain subgroups of SIDS.
As Dr Goldwater points out, pathological evidence has largely been ignored over the years, but perhaps this is not surprising as the lack of comparative baseline information and standardised postmortem protocol renders much of the pathological evidence as uncontrolled anecdotal observations. However, in conducting a SIDS study one actually conducts a study of all sudden unexpected deaths in infancy (SUDI), of which SIDS is the larger part but also includes explained deaths. Given that the relative proportion of explained SUDI deaths has now grown with the decline of unexplained SIDS deaths, the potential for a viable comparison group where the epidemiological and pathological data have already been collected is becoming an increasingly realistic proposition. Previous efforts to standardise postmortem protocols have perhaps been too complex to put into practice,4–9 and this is further compounded, at least in the UK, by a growing reluctance to carry out tests because of the negative public reaction to the past practices of tissue and organ retention. However Fleming and colleagues10 have defined an evidence based postmortem protocol that balances the probability of obtaining useful information against the needs of parents for the examination to be completed quickly, with a minimum of tissue retention. This protocol shows that with a minimum number of tests and a thorough clinical history, virtually all of the deaths for which a cause could be ascertained will be correctly identified.
If the enigma of SIDS is to be solved, the pathologists need to work closer with the epidemiologists and the funding organisations need to educate the public on why the pathologists plays such a pivotal role in trying to understand why our babies sometimes die.
A commentary on the review by Goldwater