Studies utilizing frequency-domain near-infrared spectroscopy (fdNIRS) have demonstrated that approximately 30% of multiple sclerosis (MS) patients have brain hypoxia. The effects of hypoxia on these individuals, however, are yet to be fully elucidated. Literature shows that hypoxia can induce cerebral edema, characterized by an increase in brain water content, and mitochondrial swelling. This phenomenon can be detected using NIRS technology as an increase in light scattering and may provide extensive insight into MS pathology.
The aim of our study was to determine if there are differences in light scattering and absorbance as measured by fdNIRS (OxiplexTS Frequency Domain Near-Infrared Spectrometer, ISS, USA) between controls and MS patients
fdNIRS measurements were obtained from the frontal cortex of 54 controls and 83 MS patients. The parameters measured included hemoglobin saturation in tissue microvasculature (StO2), scattering coefficient (μs) and absorption coefficient (μa) at 690 and 824 nm. Light scattering and absorption values were averaged across wavelengths. Each parameter was compared between controls and MS patients using a Student’s t-test.
As previously shown, we found that in MS patients, StO2 percentage was significantly lower than in controls (57.40±7.66 vs. 61.28±6.27, respectively, p=0.002). The mean light scattering (μs) in the MS population was significantly higher than controls (9.25±1.36cm-1 vs. 8.65±1.34cm-1, respectively, p=0.015), with no differences in the mean absorbance (μa) (0.11±0.02cm-1 vs. 0.11±0.02cm-1, respectively, p=0.99).
We report that reduced StO2 in MS patients occurs alongside an increase in light scattering with no detected difference in absorbance. These results resemble a prior study investigating NIRS parameters on acute mountain sickness, which demonstrated that an increase in light scattering without changes in absorption is indicative of hypoxia-induced cerebral edema. Cerebral edema may also be associated with mitochondrial dysfunction, which in conjunction with pre-existing hypoxia, may contribute to detrimental brain damage. Previously, we used fdNIRS to confirm the presence of hypoxia in MS. This study shows it may also be a useful tool to investigate consequential cerebral edema and or mitochondrial integrity in MS.