BACKGROUND AND PURPOSE: There is increasing evidence implicating microvascular (small blood vessel) impairment in MS. Perfusion imaging (a marker of blood flow) offers a unique opportunity to investigate the functional impact of gray matter (GM) pathology. The investigators sought to quantify differences in MR imaging-based cerebral perfusion (blood flow) between cognitively impaired and nonimpaired SPMSers.
MATERIALS AND METHODS: MSers were prospectively recruited and assessed using MR imaging and the standard cognitive battery called the Minimal Assessment of Cognitive Function in MS. MSers exhibiting impairment on ≥2 individual tests were classified as cognitively impaired. Healthy controls were prospectively recruited and assessed using MR imaging to validate assumptions. Structural and perfusion scans were coregistered (overlayed on top of each other) and partitioned into anatomic brain regions and tissue compartments. Clinical and radiologic characteristics were compared between MSers with and without impairment to identify potential confounders.
RESULTS: Thirty-seven MSers with SPMS (age 56 ± 9 years; 23 women, 14 men) and 10 age- and sex-matched healthy controls were recruited. Assumptions were found to be valid in MS. GM and WM cerebral blood flow were all globally reduced in impaired MSers. After adjusting for potential confounders while examining sublobar level perfusion, only GM cerebral blood flow was significantly different between cognitive groups, and this hypoperfusion (reduced blood flow) localized to the bilateral medial superior frontal regions and left inferior, middle, and superior frontal regions (P < .005) of impaired MSers compared with nonimpaired patients.
CONCLUSIONS: Bookend-derived GM cerebral blood flow was significantly reduced in cognitively impaired patients with SPMS in functionally relevant brain regions.
"Chicken or egg? MS is a disease with extensive gray matter involvement; it causes damage and loss of gray matter. Gray matter is metabolically active, i.e. requires glucose and oxygen to function, these are delivered by the blood. If you have lost gray matter you get reduced blood flow, i.e. the remaining tissue needs less blood. So this study is simply stating the obvious. There is no evidence that reduced blood flow precedes the loss of gray matter in MS. This is another factor that needs to be taken into account by proponents of the vascular theory of MS; shrinkage of the brain or atrophy due to loss of brain tissue occurs throughout the course of MS and is linked to reduced blood flow. Therefore detecting reduced flow in say the veins draining the brain does not imply that it is causing MS, it is simply a consequence of the loss of brain tissue."