Reduced cortical microvascular oxygenation in multiple sclerosis: a blinded, case-controlled study using a novel quantitative near-infrared spectroscopy method.
(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 (StO2). In this study, we aimed to determine if reduced StO2
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 StO2 was 63.5 ± 3% (mean ± SD). In MS patients, 42% of StO2 values were more than 2 × SD lower than the control mean. There was a significant relationship between StO2 and clinical disability. A reduced microvascular StO2
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 StO2 in patients with MS, opening the door to understanding how microvascular oxygenation impacts neurological conditions.
Figure: Measurement of brain oxygenation showing hypoxia in MS, in particular in RRMS [R] with EDSS>3 (moderate disability) and secondary progressive MS [SP]. The green shaded area represents 2 x standard deviation around the control levels.
Using infra-red spectroscopy the authors have quantified the oxygen saturation of RBCs (also called oxyhaemoglobin) in blood vessels supplying the brain grey matter region. Their data suggests that hypoxia (reduced oxygen saturation) exacerbates brain inflammation, leading to greater disease activity (R>3).
However, low levels of oxygen saturation did not directly lead to significant levels of brain atrophy, but did correlate with longer disease duration and increasing levels of disability; suggesting a paradoxical relationship between inflammation, neurodegeneration and disability levels. The reason for the paradox may be that inflammation is more closely linked to motor disability than to a global disease process per se, at least in the grey matter.
Whatever the truth of the matter, there are rarer indications for hyperbaric therapy than MS relapse.