sudden infant death syndrome michael klufas, ms iii
TRANSCRIPT
INTRODUCTION
Sudden Infant Death Syndrome (SIDS) continues to be the most common cause of postneonatal infant death 25% of all deaths between 1 month and 1 year of
age SIDS is a complex, multifactorial disorder of
which the cause is not fully understood Some environmental risk factors are
modifiable Reducing exposure to modifiable risk factors has
lowered the incidence of SIDS New research indicates genetic risk factors
Actual risk of SIDS may depend on interaction of environmental and genetic risk factors
DEFINTION
Sudden death of an infant under 1 year old that is unexpected by history and unexplained after a thorough postmortem examination
Investigation includes: Complete autopsy Investigation of the scene of death Review of medical history
EPIDEMIOLOGY
SIDS rate in United States 1990 – 1.3 per 1000 live births 2002 – 0.6 per 1000 live births ~ 3000 SIDS deaths/yr
Changes in classification of sudden unexpected deaths in infants from SIDS to categories of asphyxia and “unknown” has occurred in recent years May be falsely reducing SIDS rates while overall
death rate from unexpected infant deaths remains the same
DEMOGRAPHICS less frequently in 1st month of life Peaks 2-4 month of age 90% in first 6 months of life Boys 30-50% more likely to be affected than girls Racial and ethnic disparities
2-3x risk for African American, Native American or Alaska Native (irrespective of socioeconomic status)
African Americans twice as likely to place infants prone to for sleep & twice as likely to bedshare
High rates of smoke exposure and bedsharing among Native Americans and Alaskan Natives
Asian, South Pacific, Hispanic infants lowest incidence
Winter seasonal predominance has declined or disappeared
PATHOPHYSIOLOGY Multifactorial in origin
Triple Risk Hypothesis Vulnerable infant Critical developmental period
in homeostatic control Exogenous stressors
Final pathway believed to involve immature cardiorespiratory and autonomic control along with failure of arousal responsiveness from sleep
AUTONOMIC CONTROL AND AROUSAL SIDS infants higher baseline heart rates, lower heart rate
variability, prolonged QT indexes, lower parasympathetic tone and/or high sympathovagal balance
Abnormalities of arousal Kato and colleagues report infants who died of SIDS had
fewer spontaneous arousals from sleep and immature sleep patterns
Prone sleeping Increases total time infants spend asleep particularly
time spent in quiet sleep, a state of reduced arousability Also decreased spontaneous arousability, induced
arousability and fewer full cortical arousals Associated with altered autonomic control manifest by
raised heart rates, decreased heart rate variability and increased sympathetic tone
Infants exposed to smoking in utero have decreased spontaneous and stimulus-induced arousal from sleep
AUTOPSY FINDINGS No pathognomonic findings Common findings:
Petechial hemorrhages of thymus gland, visceral pleura in 68-95%
Pulmonary congestion (89%) and edema (63%) indicative of terminal left ventricular failure
Oronasal secretions that are typically frothy, mucoid and pink or bloody
2/3 structural evidence of pre-existing, chronic low-grade asphyxia Study identified increased VEGF in CSF of SIDS infants,
308 versus 85 pg/dL in controls Hypoxia frequently precedes death in SIDS
One study of 20 SIDS infants found 50% had levels of IL-6 in CSF equivalent to those found in infants who died of infectious diseases Staphylococcus aureus may have role in infection as 56%
of healthy infants and 86% of SIDS infants had these bacteria in the respiratory tract
NEUROANATOMICAL FINDINGS
Structural and neurotransmitter alterations in brainstem consistent with autonomic dysregulation Increase in dendritic spines (marker of delayed
neuronal maturation) and delayed maturation of synapes in medullary respiratory centers
Decreased tyrosine hydroxylase immunoreactivity in catecholaminergic neurons
Increased number and density of 5-HT neurons with decreased serotonin 1A and 2A receptor Serotonin affects various autonomic functions including cardiorespiratory and circadian rhythms
NEUROANATOMICAL FINDINGS 60% SIDS cases hypoplasia of arcuate
nucleus Vital area of autonomic control and integration Receptor abnormalities relevant to autonomic
control Decreases in binding to kainate, muscarinic cholinergic
and 5-HT receptors
Lavezzi showed alterations of the cerebellum 62% of SIDS compared to 10% controls showed
neuronal immaturity, altered apoptotic programs, negative expression somatostatin and EN2 gene, intense c-fos expression and astrogliosis in cortex and dentate nucleus
Water reported increased neuronal apoptosis in hippocampus and brainstem Neuronal loss in regions sensitive to hypoxia and
regions associated with sensation in the face
PREGNANCY RELATED FACTORS
Increased risk with: Lower
socioeconomic status
Younger maternal age
Lower maternal education
Single marital status
Mothers of SIDS infants: Less prenatal care Care initiated later in
pregnancy Low birth weight Preterm birth IUGR Shorter intervals
between pregnancies (< 18 mo)
More often 2nd or higher order birth child
SOCIAL FACTORS
SUBSTANCE USE
Major association between intrauterine exposure to cigarette smoking and risk of SIDS Risk of death is progressively greater with
increased smoking May be small independent effect of paternal
smoking An independent effect of postnatal exposure to
tobacco smoke has been found in a small number of studies as well as dose-response effect with number of household smokers
Evidence linking prenatal illegal drug is conflicting Opiates increase risk of SIDS 2-15 fold Alcohol not clearly linked, but siblings of infants
with FAS 20 fold increased risk of SIDS compared to controls
INFANT SLEEP PRACTICES & ENVIRONMENT Prone sleeping consistently shown to increase risk of
SIDS Highest risk when usually placed in another sleeping
position but were placed on stomach for last sleep, “unaccustomed prone”, more likely to occur outside the home such as day care centers
Also risk of choking highest in prone position Placing infant on side still places risk twice as likely to
die of SIDS compared to sleeping supine Exceptions may be made with certain medical
conditions Soft sleeping surfaces 2 to 3 fold increase risk of SIDS
Prone sleeping + soft bedding 20 fold increase Overheating with increased room temperature, high
body temperature, sweating or excessive clothing increase incidence No increase with high external environment
temperature No protective effect from bed sharing
Advocates of this practice typically promoters of breast feeding
1/3 reduction with sleeping in parent’s bedroom in separate crib
INFANT FEEDING PRACTICES & EXPOSURES
Association between breast-feeding and SIDS inconclusive Recent study showed breast-feeding associated with
decreased risk of postneonatal deaths overall but not decreased risk of SIDS Decreased risk with pacifier use
Not known whether direct effect or associated infant or parental behaviors
Pacifier use and dislodgement may enhance arousability
No association between pacifier use and breast-feeding duration
Small increased in otitis media, respiratory tract and GI tract illnesses
Must use consistently, one study showed increased risk of SIDS if pacifier was not used before last sleep
AAP recommends pacifier use once breast-feeding has been established
OTHER CONCERNS Upper respiratory tract infection has not
been found to be independent risk factor for SIDS However, these and other minor infections may
play a role in the pathogenesis if SIDS For instance, if in prone position, heavily wrapped or
head covered during sleep there was increased risk of SIDS with infection
Parents should be reassured that immunization does not present a risk for SIDS No temporal relation between vaccine
administration and death
Not caused by vomiting or choking
GENETICS
No specific genotypic differences in infants who died of SIDS, but several gene polymorphisms identified Generally involving
entities in cardiorespiratory, immune function and arousal
Triple risk model suggests gene polymorphisms may make certain infants more vulnerable to SIDS
This vulnerability manifests when there is an environment challenge (prone sleeping, tobacco exposure)
GENETIC RISK FACTORS
Sodium (SCN5A) and Potassium channel polymorphisms associated with long QT syndrome 5-10% of SIDS cases associated with defective
cardiac ion channel with increased potential for lethal arrhythmia
Polymorphisms in serotonin transporter (5-HTT) gene Increased in transporter activity, reducing 5-HT concentrations
at nerve endings Autonomic nervous system development genes
(PHOX2A, RET, ECE1, TLX3, EN1) Polymorphisms in promoter of anti-inflammatory
cytokine IL-10 decreased antibody production and increased inflammatory cytokines
SIDS infants w/mild respiratory infections before death were more likely than SIDS infants without infection and controls to have deficient complement C4 gene (C4A, C4B)
DIAGNOSIS By definition, SIDS is a diagnosis of exclusion Protocols for standardized autopsies and death scene
investigations have been published However, wide variability in protocols in both content and
frequency with which they are implemented across jurisdictions, within countries and across different countries
Cause of death can be difficult to diagnose from autopsy alone Examination of circumstances present immediately before
death including detailed description of sleep environment have been increasingly emphasized in recent years
Surveys of medical examiners and coroners have reflected how much more complicated, confusing and time consuming SIDS case have become Most also noted they used to label many more infant death
cases as SIDS than they do now This may be an effect of confusing risk factors for SIDS
Reaching consensus internationally on a classification scheme is essential to accurately monitor trends and direct future research
RISK REDUCTION Campaign to reduce risk of SIDS
began in 1994 in the United States Largely focused on reducing prone
sleeping and promoting supine positioning
Some campaigns also included messages to reduce smoking during pregnancy No significant changes in these behaviors
and reduced SIDS rates mostly attributed to avoidance of prone sleeping
Breast-feeding advocates have opposed discouraging bed sharing as they worry these measures will reduce breast-feeding frequency and duration and prevent families from enjoying the experience and benefits of bed sharing
MANAGEMENT AND SUPPORT Loss of infant is devastating for everyone
concerned In addition to loss of infant, families face could
face police investigation, long wait for autopsy results and continued uncertainty leading to prolonged emotional distress consequently affecting the grieving process
Physician can play active role by advocating for an autopsy, discussing autopsy results with the family and providing emotional support
Surviving siblings and other family members need age appropriate emotional support
If appropriate refer family for genetic counseling and/or metabolic testing
Direct family to local counseling and support groups which are available in most communities
FUTURE DIRECTIONS Despite decrease in prevalence of SIDS, more work is
needed Elucidation of risk and protective factors with
appropriately targeted and implemented interventions leading to increased adoption by families
Unlikely disorder is completely eliminated or reduced to lowest possible rates until specific causative mechanisms are more fully understood Need studies with larger sample sizes and infants from
highest risk groups Investigations of still births and sudden unexplained
deaths in children over 1 year of age might provide additional insights
Surveillance of trends in rates of SIDS comparisons across jurisdictions and internationally according to a universal, standardized classification protocol
Will require multidisciplinary and collaborative effort to understand more
REFERENCES Hunt CE, Hauck FR. Sudden infant death syndrome. Cmaj.
Jun 20 2006;174(13):1861-1869. Moon RY, Horne RS, Hauck FR. Sudden infant death
syndrome. Lancet. Nov 3 2007;370(9598):1578-1587. Weese-Mayer DE, Ackerman MJ, Marazita ML, Berry-Kravis
EM. Sudden Infant Death Syndrome: review of implicated genetic factors. Am J Med Genet A. Apr 15 2007;143A(8):771-788.
Gurbutt D, Gurbutt R. Risk reduction and sudden infant death syndrome. Community Pract. Jan 2007;80(1):24-27.
Fleming P, Blair PS. Sudden Infant Death Syndrome and parental smoking. Early Hum Dev. Nov 2007;83(11):721-725.
Damato EG. Safe sleep: can pacifiers reduce SIDS risk? Nurs Womens Health. Feb 2007;11(1):72-76.
Haycock G. Recent research in sudden infant death syndrome. J Fam Health Care. 2007;17(5):149-151.