Third brain stem defect found in SIDS infants

by Ralph A. Franciosi, MD

Ralph Franciosi, MD, was medical adviser for the Infant Death Center of Wisconsin and pathologist at Children's Hospital of Wisconsin. He also was a professor of Pathology and Laboratory Medicine at the Medical College of Wisconsin.

Researchers recently have discovered a third defect in the brainstem of SIDS infants.
Dr. Hanna Kinney and her colleagues, researchers at Boston Children's Hospital and Harvard Medical School in Boston, studied the brain stem, which is critical for responding to challenges during sleep, such as prone sleep position. They recently published an article that uncovered a third defect in the brain stem network that integrates vital functions during sleep, such as regulation of breathing, heart rate, body temperature and arousal. This is additional "proof" that SIDS victims have a developmental flaw. The vulnerable infants cannot respond normally to environmental challenges during sleep.

"These findings show that SIDS infants have a more global biological deficit than we previously believed - one that may originate early in fetal life," said Dr. Marian Willinger, National Institute of Child Health and Human Development, Pregnancy and Perinatology branch.

Researchers have found that structures in the brain stem of SIDS infants were less likely to bind the neurotransmitter serotonin than were the brain stems of infants who died of other causes. These findings build upon the results of an earlier study, in 1984, that found abnormalities in the brain stem region, known as the arcuate nucleus, in children who died of SIDS.

This earlier study was a major breakthrough because it made the association between sleep and control of breathing. Dr. Michael Chase, a sleep researcher from the Brain Research Institute at the University of California, was first to suggest that there are brief moments during the development of physiologic systems when there is a changeover from one set of circuitry to another or when specific physiologic functions are particularly labile.

"It is at these critical crossroads in time that the infant may be particularly at risk for SIDS," Chase said.

This recent research reinforces the theory that SIDS is a disorder of fetal development. But, how can we prove that SIDS is a developmental flaw if we cannot see lethal tissue changes?
Infants who die from non-SIDS causes have tissue changes that explain the death. SIDS cases, however, do not show any lethal tissue changes. Unfortunately, at autopsy, non-SIDS as well as SIDS infants, can show tissue changes that do not explain the death, but are misinterpreted as a cause of death.

The diagnosis of SIDS is unique because no specific diagnostic test is presently available. Unfortunately, the existence of SIDS can be questioned because of the lack of medical explanation. Another example of this is an infant who dies of hypoventilation syndrome, an inability to initiate breathing while asleep. There is no specific test at autopsy to confirm the diagnosis, but this condition, although rare, is well known to pediatricians and its existence cannot be denied.

There are many problems in medicine we do not understand. It is important to have a diagnosis, however, in order to provide a framework for case management and research. To diagnose SIDS, it is important the diagnostician, a pathologist, be knowledgeable about the national diagnostic criteria, as well as with the examination of infant tissues.

There is much work that needs to be done to understand the mechanisms associated with SIDS, as well as to make sure SIDS cases are consistently diagnosed according to national guidelines. I, along with my colleagues Dr. Forster and Dr. Wong-Riley both at the Medical College of Wisconsin, will continue to collaborate with Dr. Filiano, Children's Hospital and Darthmouth Medical School, New Hampshire, and Dr. Kinney, on these and other issues.

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