From MedscapeCME Clinical Briefs

Cognitive and Structural Gray Matter Deficits Linked to OSA 

News Author: Laurie Barclay, MD

 

November 16, 2010 — Cognitive and structural gray matter deficits linked to obstructive sleep apnea (OSA) may be reversible with continuous positive airway pressure (CPAP), according to the results of a study reported online October 29 in the American Journal of Respiratory & Critical Care Medicine.

"OSA patients demonstrate several neuropsychological impairments, but current knowledge of the brain structures affected by OSA is limited," said corresponding author Vincenza Castronovo, PhD, clinical psychologist at the Sleep Disorders Center, Vita-Salute San Raffaele University and San Raffaele Scientific Institute in Milan, Italy, in a news release. "This study provides the first evidence that structural brain abnormalities exist in regions susceptible to hypoxemia, and they can change with treatment."

The goal of the study was to assess the cognitive deficits and the corresponding brain morphologic changes in OSA and changes after treatment, using combined neuropsychological testing and Voxel-Based-Morphometry in 17 treatment-naive patients with OSA and 15 age-matched healthy control subjects.

Sleep study, cognitive tests, and magnetic resonance imaging were performed in all participants at baseline, and cognitive testing and magnetic resonance imaging were repeated after 3 months of treatment.

Before CPAP treatment, patients with OSA had impairments in most cognitive areas, as well as in mood and sleepiness, which were associated with focal reductions of gray-matter volume in the left hippocampus (enthorinal cortex), left posterior parietal cortex, and right superior frontal gyrus.

"We found reduced GM-[gray matter]volume in the OSA group when compared to the non-OSA group in several key regions of the brain," Dr. Castronovo said. "Of particular note were the deficits in the left parahippocampal gyrus and in the left posterior-parietal cortex. We found that these two regions have significant bearing on abstract reasoning and executive function. Deficits in the left posterior-parietal cortex were also shown to be associated with daytime sleepiness."

After treatment, there were significant improvements in memory, attention, and executive functioning, and parallel increases in gray-matter volumes in the hippocampal and frontal structures.

"These results suggest a scenario in which the hippocampus, due to its sensitivity to hypoxia and innervation of small vessels, is the region that is most strongly and quickly affected by hypoxic episodes," Dr. Castronovo said. "The mechanism of the observed brain changes could be either neurogenic or vasogenic. We propose it to be vasogenic."

Limitations of this study include failure to reevaluate healthy control participants at 3 months and lack of generalizability to nonhypoxic sleepy patients.

"Next, our group will focus on increasing our understanding of brain damage and recovery," Dr. Castronovo concluded. "We want to evaluate non-hypoxic sleep disordered breathing in sleepy patients to assess the role of hypoxia in structural brain involvement."

Respironics Foundation, Pittsburgh, Pennsylvania, supported this study. The study authors have disclosed no relevant financial relationships.

Am J Respir Crit Care Med. Published online October 29, 2010.

Clinical Context

Study Highlights

• In this study, 17 treatment-naive patients with OSA and 15 age-matched healthy control participants all underwent a sleep study, cognitive tests, and magnetic resonance imaging.
• Inclusion criteria for OSA were an apnea/hypopnea index of more than 30.
• Inclusion criteria for control participants were an apnea/hypopnea index of less than 5, and participants had to be free of psychiatric and medical disorders.
• There were no significant demographic differences between patients and control participants.
• The neuropsychological evaluation involved short-term and long-term memory, executive functions, constructional abilities, vigilance, attention, and abstract reasoning. Additionally, participants completed the self-report Epworth Sleepiness Scale to evaluate daytime somnolence, the Beck Depression Inventory to evaluate mood, and the 36-item Medical Outcomes Study Short-Form Health Survey to assess overall quality of life.
• After 3 months of treatment, cognitive and imaging data were collected to assess therapy efficacy.
• Neuropsychological results in pretreatment OSA showed impairments in most cognitive areas, as well as in mood and sleepiness.
• These impairments were associated with focal reductions of gray-matter volume in the left hippocampus (enthorinal cortex), left posterior parietal cortex, and right superior frontal gyrus.
• After treatment, significant improvements were observed involving memory, attention, and executive functioning that paralleled gray-matter volume increases in the hippocampal and frontal structures.
• The left anterior parahippocampal gyrus was associated with gray-matter volume increases after treatment, correlating with improved performance in the Digit-Span Forward (short-term memory), Corsi (short-term memory), and Stroop test (executive function).
• A significant gray-matter volume increase in the left cornu-ammonis correlated with improvement in the Stroop test.
• Overall, patients showed significant improvement in sleepiness and in all cognitive tests.
• A limitation of the study was that healthy control participants were not reevaluated at 3 months because of study costs and participant availability for repeated magnetic resonance imaging scanning.

Clinical Implications

• OSA is associated with neurocognitive and cardiovascular morbidities, reduced quality of life, impaired work performance, and an increased risk for vehicular crashes and industrial injuries.
• The cognitive and structural deficits associated with OSA may be recovered with consistent treatment, with magnetic resonance imaging changes representing a marker for treatment response.