Reduced cortical microvascular oxygenation in multiple sclerosis: a blinded, case-controlled study using a novel quantitative near-infrared spectroscopy method

Hypoxia (low oxygen) is associated with many brain disorders as well as inflammation, but the lack of widely available technology has limited our ability to study hypoxia in human brain. Multiple sclerosis (MS) is a poorly understood neurological disease with a significant inflammatory component which may cause hypoxia. We hypothesized that if hypoxia were to occur, there should be reduced microvascular hemoglobin saturation (S(t)O(2)). In this study, we aimed to determine if reduced S(t)O(2) can be detected in MS using frequency domain near-infrared spectroscopy (fdNIRS). We measured fdNIRS data in cortex and assessed disability of 3 clinical isolated syndrome (CIS), 72 MS patients and 12 controls. Control S(t)O(2) was 63.5 ± 3% (mean ± SD). In MS patients, 42% of S(t)O(2) values were more than 2 × SD lower than the control mean. There was a significant relationship between S(t)O(2) and clinical disability. A reduced microvascular S(t)O(2) is supportive (although not conclusive) that there may be hypoxic regions in MS brain. This is the first study showing how quantitative NIRS can be used to detect reduced S(t)O(2) in patients with MS, opening the door to understanding how microvascular oxygenation impacts neurological conditions.