Sudden Unexpected Infant Deaths
Ling Li
Each year in the United States, more than 4, 500 infants die suddenly without obvious cause. The terminology used to classify these deaths is still a work in progress and is somewhat confusing. The term “sudden unexpected infant death” (SUID) applies to all sudden death in infants before determination of the cause/manner of death (i.e., before completion of pertinent investigation and autopsy). If the cause or manner of death remains undetermined, in the State of Maryland we use the term “sudden unexplained death in infancy” (SUDI). Half of SUIDs are due to sudden infant death syndrome (SIDS), which is also the leading cause of all deaths among infants ages 1 month to 12 months.1 The sudden, unexpected death of an infant arouses profound emotions in a death investigation. The inevitable and invariable question is, “Why did this baby die?” The question is shrouded in feelings of helplessness, together with doubt, suspicion, guilt, and fear. Infants who are apparently healthy are not supposed to die2; there must be a reason.
About 50 years ago, the medical community began a search to understand and prevent sudden infant deaths.3, 4 Rendering a medicolegal opinion regarding the cause and manner of SUID challenges the intellect and sensibilities of coroners, medical examiners, and forensic pathologists. To reach a proper conclusion for the cause of death in infants who died suddenly and unexpectedly, both a thorough investigation of the circumstances of the death and a complete autopsy examination are essential to provide a reliable conclusion. Omission of one of these elements can place the entire cause of death and manner of death in question. The role of the neuropathologist in the investigation of SUID is important to exclude pathologic processes in the brain that could cause the death or contribute to it. Among these pathologic processes, the most important ones to rule out are trauma, infections, and developmental abnormalities.
Several important entities should be considered in the investigation of SUIDs:
SIDS
SUDI (sudden infant deathwith undetermined/unspecified causes)
Accidental or unintentional asphyxia
Metabolic/genetic diseases
Environmental mechanisms of death
Infanticide (see Chapter 16)
SUDDEN INFANT DEATH SYNDROME
Definition
The definition of SIDS was originally introduced at the second International Conference on Causes of Sudden Death in Infants in 1969 as “the sudden death of an infant or young child which is unexpected by history, and in which a thorough postmortem examination fails to demonstrate an adequate cause of death.”5
The term SIDS was modified two decades later. In 1989, the National Institute of Child Health and Human Development convened an expert panel to re-examine the definition. The panel defined SIDS as “the sudden death of an infant under one year of age, which remains unexplained after a thorough case investigation, including performance of a complete autopsy, examination of the death scene, and review of the clinical history.”6
Although there is ongoing discussion about changing the definition, 7 the current generally accepted definition of SIDS remains as above.
Incidence and Epidemiology
Beginning with the establishment of the SIDS diagnosis in 1969, SIDS rates in the United States rose rapidly until 1980, then fell dramatically from 1992 to 2001. In the United States in the1980s, approximately 6, 000 infants succumbed to SIDS per year, representing a rate of 1.5 per 1, 000 live births overall and making SIDS the second most common cause of infant death in aggregate of all racial and ethnic groups.8 Since 1992, there has been a sustained reduction in the SIDS rate. Between 1992 and 2001, the total SIDS rate in the United States decreased from 1.2 deaths to 0.56 deaths per 1, 000 live births, a 55% decrease over 10 years.9, 10 The rate in 2002 remained constant at 0.57 per 1, 000 live births.11 The National Center for Health Statistics reported12 that in 2004, SIDS accounted for 2, 247 infant deaths, representing 8% of infant deaths and making SIDS the third leading cause of all infant deaths in the United States.
Typically, SIDS is suspected when a previously healthy baby, usually 6 months of age or younger, dies, apparently during sleep, prompting an urgent call for emergency assistance.2, 13 The incidence of SIDS reaches a peak between 2 and 4 months of age. Few cases occur in the first week of life, and approximately 90% of SIDS cases occur by 6 months of age.14, 15 The characteristic age distribution has become less pronounced in some countries as the SIDS incidence has declined, with occurrence of deaths at earlier ages and flattening of the peak incidence.16, 17
There is a substantial sex difference in SIDS deaths, with male predominance (60% to 70%). SIDS rates are two to three times higher among African American, Alaska native, and some American Indian populations, whereas Asian, South Pacific, and Hispanic infants have the lowest incidence rates.11, 13, 18, 19, 20 In the United States, the race difference in SIDS has been attributed to
differences in socioeconomic status.19 SIDS occurs more frequently in the winter in both the northern and southern hemispheres, and it is seen more often in multiple births with twins and triplets than in single births.
differences in socioeconomic status.19 SIDS occurs more frequently in the winter in both the northern and southern hemispheres, and it is seen more often in multiple births with twins and triplets than in single births.
Risk Factors and Etiology
A number of factors, both modifiable and unmodifiable, have been identified across studies as risk factors for SIDS.15, 19, 20, 21, 22, 23, 24, 25 Significant risk facts include the following:
Prone sleeping position
Maternal smoking during pregnancy
Prematurity
Low birth weight
Inadequate prenatal care
Young maternal age
Lower socioeconomic status
Male sex
Less significant risk factors include the following:
Postnatal exposure to tobacco smoke
Side sleeping position
Soft sleeping surface, soft bedding
Increased parity
Short interval between pregnancies
Lower maternal education level
Single marital status
Overheating
Sleeping in own room rather than in parents’ room
Maternal prenatal illicit drug use
Possible risk factors with conflicting data include maternal prenatal or postnatal alcohol use and sharing a bed with parents or siblings. Other important factors related to SIDS are as follows:
SIDS is neither predictable nor preventable.
SIDS is neither contagious nor hereditary.
SIDS is not caused by smothering or choking due to aspiration of regurgitated or vomited food.
There is no causal relationship between SIDS and vaccinations.
Supine sleeping alone in a crib or bassinet and use of a pacifier at bedtime and naptime reduce the risk of SIDS.
Use of infant home monitors is not recommended as a strategy for preventing SIDS, but use of monitors may be helpful to allow rapid recognition of an apparent life-threatening event, such as apnea, airway obstruction, respiratory failure, interruption of supplemental oxygen supply, or failure of mechanical respiratory support.
Although breastfeeding is beneficial and should be promoted for many reasons, the evidence is currently insufficient to recommend breastfeeding as a strategy for reducing SIDS.
In the past, many theories and hypotheses were postulated to explain SIDS deaths. For many years, victims of SIDS were regarded as having been previously normal, and their deaths were unexpected by history.26 Disorders of cardiac conduction (QT prolongation, heart rate abnormalities) leading to lethal arrhythmias27, 28 and idiopathic prolonged sleep apnea29, 30 were early considerations in the etiology of SIDS. At the present time, after many years of study, there are no consistent data to show a significant abnormality of the cardiac conduction system in SIDS victims, nor is there absolute proof that apneic spells commonly seen in premature infants and SIDS are related.31, 32
The hypothesis of brainstem abnormalities as a possible cause of SIDS has been studied by many scientists. A subtle defect in the brainstem neural circuits that control respiration and/or cardiovascular stability during sleep was thought to play a major role leading to SIDS.33, 34, 35, 36 Brainstem gliosis, 33 hypoplasia of the arcuate nucleus, 34 abnormalities of the neurotransmitter systems (particularly decreased muscarinic receptor binding in the arcuate nucleus35), and medullary serotonergic network deficiency36 have all been described as possible clues to the role that the central nervous system may play in dysfunction of cardiorespiratory control resulting in SIDS. The brainstem abnormalities found in SIDS victims, however, have also been found in controls, with known chronic hypoxia.37 Therefore, the questions of cause versus effect of the abnormalities, and whether they occurred prenatally or postnatally, remain unanswered.38
In recent years, the cause of SIDS is presumed to be multifactorial, with interaction of risk factors of variable probabilities.38
A “triple-risk hypothesis” has received great attention. The triple-risk model involves three types of risk factors: (1) a vulnerable infant who possesses some underlying abnormality; (2) a critical period in development; and (3) an exogenous stressor, such as respiratory infection.39 On the basis of the triple-risk hypothesis, an infant will die of SIDS only if the infant has all three factors; the infant’s vulnerability lies latent until he or she enters the crucial period and is subject to an exogenous stressor. The National Institute of Child Health and Development40 has stated unequivocally in its SIDS Strategic Plan 2000 that “SIDS is a developmental disorder. Its origins are during fetal development.” Although new theories regarding the cause of SIDS seem to arise every few years, at the present time, the exact mechanism of death remains unknown.
Scene Investigation
SIDS is in essence a diagnosis of exclusion. The successful investigation of any SUID requires a multi-agency, multidisciplinary approach and adherence to the standard protocols of death scene investigation and autopsy examination. In 1992, the US Senate and US House of Representatives recommended the US Department of Health and Human Services Interagency Panel on SIDS establish standard scene investigation protocols for SUID. The Sudden Unexplained Infant Death Investigation Report Forms (SUIDIRF), which have a short and an expanded format, were published in 1996.41
In 2004, the US Centers for Disease Control and Prevention (CDC) launched a national initiative to further improve the investigation and reporting of SUID. As a part of this initiative, the CDC convened a national workgroup to improve the utility and acceptability of the 1996 SUIDIRF in an effort to standardize infant death scene investigation and reporting of all SUIDs.42, 43, 44 The revised SUIDIRF has been posted at the CDC SIDS/SUID web site.45
In all sudden infant death cases, a thorough scene investigation should be made. If the body has not been removed, investigators should go to the scene and document what they find. If the body has been removed before the investigation, the death scene should be reconstructed by trained professional investigators. The parents and/or individuals taking care of the child should be interviewed. The following information should be collected during the death scene investigation:
Death scene location and sleeping environment, such as condition of the bedding, materials in the bed, sleeping location, sleeping position (placed position and found position), bed sharing, and room temperature where the child was found
Infant’s history, including age, sex, race, prenatal care, birth, development, and medical history; the last time the child was seen alive and by whom; the last time the child was fed; and the time the child was found and by whom
Caregiver’s history, such as socioeconomic and educational background, any involvement of health and social agencies, and history of smoking, alcohol, and drug use
Death scene investigations have proven to be important in differentiating SIDS from other sudden infant deaths. One example of the importance of scene investigation is illustrated by the following case history.
Case 15.1
A 4-month-old infant, reported as being in good health, was found dead in his crib. The initial investigation revealed that the child was under the care of the mother. There were no external signs of injury. The case was initially presented as probable SIDS by the investigator. An autopsy was performed, and no significant abnormalities were detected except for the anterior lividity, with pallor around nose and mouth.
A follow-up scene investigation revealed that the crib was full of baby clothes and some plastic shopping bags. The mother, when interviewed again, revealed that the infant had been found face down with his head entangled in the plastic bags. The mother admitted that she did not tell the truth about how the child was found when she was interviewed by the investigator previously because she was afraid she would be charged with killing her child.
At the scene, the investigators should approach the parents and other caregivers in a sensitive, sympathetic, and nonaccusatory manner and should interview, not interrogate. The parents and caregivers should be permitted to tell their story without interruption.
Postmortem Examination
The American Academy of Pediatrics and the National Association of Medical Examiners endorse universal performance of autopsy on infants who die suddenly and unexpectedly, conducted by forensic pathologists experienced in the diagnosis of SIDS.46 Studies to be considered at postmortem examination are as follows:
Full skeletal radiologic study
Gross and histologic examination, including examination of the brain and spinal cord
Microbiologic study
Toxicologic and chemistry studies
Metabolic and genetic studies
Full-body radiographic skeletal surveys should be performed before autopsy in cases of SIDS. A radiographic skeletal survey may reveal evidence of traumatic skeletal injury or skeletal abnormalities indicative of a naturally occurring illness. A gross autopsy examination should be carried out, along with auxiliary studies such as histology, microbiology, toxicology, and metabolic/genetic tests.
There are no routine autopsy findings pathognomonic of SIDS, and no findings are required for its diagnosis. There are, however, some common observations, which have often been referred to as classic or typical findings.47, 48, 49 Frequently, the baby is found to have a little bloody foam about the nares and/or mouth. This may stain bedclothes and suggest abuse, but is due to terminal pulmonary congestion and edema. Petechial hemorrhages are commonly seen on the surfaces of the organs and the pleura and are most striking in the thymus.
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