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Magnetic Resonance Spectroscopy (MRS) is a way of evaluating local metabolic chanes in the brain; it has been used with tumors, strokes, multiple sclerosis, Alzheimer's Disease, and epilepsy, but never previously in cases of sleep apnea. In this study, 23 patients with sleep apnea, 19 men and 4 women, ages 24-75 (average=48), 11 with mild apnea (indices less than 20) and 12 with moderate to severe apnea (indices greater than 20) were compared with 15 healthy subjects of similar ages, on Magnetic Resonance Imaging, a way of visualizing brain structure, as well as Magnetic Resonance Spectroscopy. All studies were done in the waking state.
The authors found significant differences in the cerebral white matter (which contains nerve fibres as contrasted to nerve cell bodies) in moderate to severe sleep apneics versus both mild sleep apneics and controls, but no differences between mild sleep apneics and controls. The specific changes involved, though uncertain in significance, have been seen in various conditions associated with injury to nerve fibres or loss of nerve cells, though the changes were smaller than those observed in other brain diseases. This suggested the presence of brain damage caused by apneic episodes, possibly as a result of hypoxia (lack of oxygen). Note that no structural damage was visible on the MRIs. The authors suggested that MRS studies should be done on follow-up to see if the abnormality reverses with treatment, and during sleep to see if the changes are attributable to hypoxia.
Although the study of neuropsychological testing abnormalities in even mild sleep apneics has already suggested the presence of brain malfunction associated with the disease, this study is to my knowledge the first to show actual localized metabolic changes in the brain suggestive of brain injury in sleep apnea. It needs to be replicated, as well as studied after treatment and during sleep as the authors suggest. The evidence for neuropsychological impairment is more extensive than the neuroradiologic evidence, but the coming together of the two lines of evidence is concerning to those of us sleep apneics who may, as I have, noticed problems with attention or memory. The usual neurologic tests given to assess brain structure and function--the electroencephalogram (EEG), computerized tomography (CT) scan, and magnetic resonance imaging (MRI) studies, are all fairly gross measures compared to the MRS technique used here. In general in sleep apneics, as in my case, EEG, CT, and MRI are all normal; I don't know how widely available MRS is at present.
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