What Causes SIDS?

Patient Presentation
A 74-day-old premature twin male stopped breathing while on his father’s lap. His father was doing computer work and stated that he looked down and the baby was no longer alive. The baby was lying on his back and not swaddled in a blanket.
His father states that there were no sounds or struggling. The father also said that he had no idea how long it had been since he had noted the baby to be alive. The baby was not revived with cardiopulmonary resuscitation.
The past medical history revealed a twin male who had been in the neonatal intensive care unit with some episodes of apnea after birth. He did not go home with an apnea/bradycardia monitor and had been otherwise healthy.
The twin had also been healthy.
The review of systems revealed that the father said that the infant’s breathing was labored but that it seemed like a cold.
A full work-up included an investigation by the local police department for possible child abuse. The diagnosis of sudden infant death syndrome was made. The father later was told that the most likely cause was acid reflux leading to heart and respiratory failure.

Sudden Infant Death Syndrome (SIDS) is a clinical diagnosis with the sudden death of an under one year of age infant that remains unexplained after a thorough case investigation, including examination of the scene of death, a complete autopsy, and review of the clinical history.
Cases not meeting these standards, should not be classified as SIDS, such as those without an autopsy.

SIDS is the most common cause of death in the postneonatal period (i.e., in infants aged 1 month to 1 year).
Most occur in infants 2-4 months, with 90% of cases occuring in &lt; 6 month old infants, and 95% of deaths occuring in < 8 month old infants.
The male-to-female ratio is 3:2 in most population studies, and SIDS is higher in African Americans and Native Americans for unknown reasons.

After studies completed in multiple developed countries internationally, the U.S. began recommending placing infants on their back for sleeping, i.e. the “Back to Sleep” campaign in 1994.
SIDS rates have fallen approximately ~75% since then. In 2002, a total of 2295 SIDS deaths were reported nationwide.

An ALTE (apparent life-threatening event) is different than SIDS and is defined as an event “???that is frightening to the observer and is characterized by some combination of apnea (central or obstructive), change in muscle tone (usually diminished), and choking or gagging.”ALTE frequency in healthy term infants is estimated to be 1-3%. The subsequent death among infants with an ALTE is 1-2%. The rate increases to 4% if the infant had respiratory syncytial virus, and goes up to 8% if the infant had the ALTE during sleep or required cardiopulmonary resuscitation. Thus, there may be a relationship between ALTE and SIDS.

Learning Point
The cause or causes of SIDS is not currently known. Many people believe that SIDS is multifactorial. Potential causes of SIDS include:

  • Triple risk model – where an infant with intrinsic abnormalities of cardiorespiratory control is in a critical period of homeostatic cardiorespiratory development, and then has external stressors that cause the infant to have inadequate cardiorespiratory homeostasis and results in cardiorespiratory failure.
    • Critical developmental period – the peak time period for SIDS is also the time when the brain undergoes rapid developmental change for sleep, arousal, cardiorespiratory homeostasis and metabolism.
    • Stressors could include the concentration of oxygen and carbon dioxide in the infant’s microenvironment, temperature, and infections. This may explain why smoking, especially maternal smoking, appears to increase the risk of SIDS.
      Additionally, asphyxiation though co-sleeping and prone sleeping may also be explained though this mechanism.
      This may also explain why the father of the patient in the case above was told that acid reflux may have been the cause of his son’s death (e.g. possibly through aspiration leading to asphyxia).
  • Neurodevelopmental pathology – various studies have found differences in neurotransmitters and neuropathways in various parts of the brain. These include dopamine, tyrosine and serotonin. Potentially involved areas include the medulla, cerebellum, and pre-frontal cortex.
    A recently study found medullary sertonin pathology to be more extensive in SIDS than previously thought.
    An increased risk of SIDS in premature infants may possibly be explained through this mechanism.

  • Long QT Syndrome – may contribute to some cases of SIDS. It appears that certain sodium channel mutations, such as SCN5A, may contribute to arrhythmias and thus potentially death.
  • Fatty acid oxidation defects – At autopsy some infants have fatty changes in their liver. Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is a proposed cause.
  • Child abuse – is estimated to cause 1-10% of all unexplained, sudden deaths in infancy. Most SIDS cases do not have any risk factors for child abuse, but it does emphasize the need for a through death investigation to be completed.

Questions for Further Discussion
1. What are current indications for using an apnea/bradycardia monitor?
2. What are the recommendations for using pacifiers, bundling of infants and side-lying sleeping position?

Related Cases

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Information prescriptions for patients can be found at MedlinePlus for this: Sudden Infant Death Syndrome (SIDS).

To view current news articles on this topic check Google News.

Carolan PL. Sudden Infant Death Syndrome. eMedicine.
Available from the Internet at http://www.emedicine.com/ped/topic2171.htm (rev. 6/8/2006, cited 1/22/07).

Paterson DS,
Trachtenberg FL,
Thompson EG,
Belliveau RA,
Beggs AH,
Darnall R,
Chadwick AE,
Krous HF,
Kinney HC. Multiple serotonergic brainstem abnormalities in sudden infant death syndrome. JAMA. 2006 Nov 1;296(17):2124-32.

Wang DW, Desai RR, Crotti L, Arnestad M, Insolia R, Pedrazzini M, Ferrandi C, Vege A, Rognum T, Schwartz PJ, George AL Jr.
Cardiac Sodium Channel Dysfunction in Sudden Infant Death Syndrome.
Circulation. 2007

ACGME Competencies Highlighted by Case

  • Patient Care

    5. Patients and their families are counseled and educated.

    9. Patient-focused care is provided by working with health care professionals, including those from other disciplines.

  • Medical Knowledge
    10. An investigatory and analytic thinking approach to the clinical situation is demonstrated.
    11. Basic and clinically supportive sciences appropriate to their discipline are known and applied.

  • Practice Based Learning and Improvement
    12. Evidence from scientific studies related to the patients’ health problems is located, appraised and assimilated.
    13. Information about other populations of patients, especially the larger population from which this patient is drawn, is obtained and used.

  • Professionalism
    20. Respect, compassion, and integrity; a responsiveness to the needs of patients and society that supercedes self-interest; accountability to patients, society, and the profession; and a commitment to excellence and on-going professional development are demonstrated.

    Donna M. D’Alessandro, MD
    Associate Professor of Pediatrics, Children’s Hospital of Iowa

    February 5, 2007