Possible Brain Damage Seen in Children With Sleep Apnea

BALTIMORE, Aug. 22 -- Children with obstructive sleep apnea may suffer hypoxic damage to brain areas governing learning, memory, and executive function, according to a study here.

Magnetic resonance imaging (MRI) measurements of metabolic activity in the brains of these children found abnormalities "indicating possible neuronal injury" in the left hippocampus and right frontal cortex, reported Ann C. Halbower, M.D., of Johns Hopkins, and colleagues, in the August issue of PloS Medicine.

Previous studies have suggested that obstructive sleep apnea is linked to learning and memory problems and poor school performance in children, but this is the first study to use MRI to identify what might be actual corresponding damage in these developing brains, Dr. Halbower and colleagues said.

Identifying and treating such damage is important, the researchers said, "since childhood obstructive sleep apnea impacts a rapidly developing brain, and thus the long-term consequences of neuronal injury may be far greater than those seen in adults."

The study included 19 children with moderate to severe obstructive sleep apnea, ages six to 16, and 12 healthy age, gender, ethnicity, socioeconomic status-matched controls. The children underwent sleep tests, IQ tests, and other neuropsychological assessments, including tests of executive function. Most of the children also underwent proton magnetic resonance spectroscopy imaging.

Proton magnetic resonance spectroscopy imaging detects levels of brain metabolites such as N-acetyl aspirate (NAA) and choline (Cho). A low ratio of NAA/Cho is often evident in ischemic brain injury and adult obstructive sleep apnea, the investigators said.

Compared with the control group, children with obstructive sleep apnea had decreased NAA/Cho ratios in the left hippocampus (control group ratio: 1.29, sleep apnea group ratio: 0.91; P=0.001). The sleep apnea group also had decreased ratios in the right frontal cortex (controls: 2.2, sleep apnea group: 1.6; P=0.03).

The sleep apnea group also scored significantly lower on the IQ test (a mean score of 85.8 versus 101; P=.002) and on measures of executive function, including verbal working memory (P=.015) and word fluency (P=.018).

There were trends toward the children with sleep apnea scoring lower on tests of visual-spatial memory and verbal memory, but these did not reach statistical significance. "With a larger sample, statistically significant differences between groups on these measures might be detected," the researchers said.

However, the children with sleep apnea did not score significantly lower on tests measuring problem solving and planning, inhibition control, sustained attention, and vigilance. All of these have been reported to be impaired in adults with sleep apnea, the investigators said. In addition, imaging studies of these adults have identified abnormal morphology in the frontal cortex, cerebellum, and hippocampus, the researchers added.

The brain damage might be caused by hypoxia resulting from the obstructed breathing and gas exchange abnormalities characteristic of sleep apnea, the authors speculated.

"While these findings do not necessarily indicate a causal relationship between obstructive sleep apnea and neuronal abnormality (i.e., it is not known whether sleep apnea causes brain damage or pre-existing brain damage causes sleep apnea)," they said, "it will be important to determine to what extent these findings reverse with treatment."

"We speculate that untreated childhood obstructive sleep apnea could permanently alter the trajectory of a developing child's ultimate cognitive potential, resulting in a lifetime of health and economic impacts," they said.

"Future studies will need to address the effect of treatment, and explore gender- and age-related differences in vulnerability to help target early diagnosis and treatment most effectively," they concluded.