Changes in cerebral blood flow and oxygen metabolism related to magnetic resonance imaging white matter hyperintensities in Alzheimer's disease

We studied changes in cerebral perfusion and oxygen metabolism to elucidate the pathophysiological nature and clinical significance of white matter hyperintensities in Alzheimer's disease (AD). Methods: Sixteen AD patients (age 71.6 ± 3.1 yr) whose T2-weighted MR images showed white matter hyperintensities, and 16 age-matched AD patients (age 71.0 ± 4.3 yr) without white matter hyperintensities were compared. Regional cerebral blood flow (CBF), oxygen metabolism (CMRO₂) and oxygen extraction fraction (OEF) were measured by using ¹⁵O steady-state method and PET. Results: There was no significant difference in cognitive impairment between the two groups. Compared to the patients without white matter hyperintensities, those with them had significantly low CBF values and significantly high OEF values in all cortical and white matter regions. However, there were no significant differences in CMRO₂ values between the two groups. Severity of white matter hyperintensities correlated with the mean cortical and mean white matter OEF. Conclusion: In AD patients, white matter hyperintensities on T2 weighted MR images represent ischemic changes in which oxygen metabolism and function are fairly compensated. These changes are not disease-specific but are age- associated coincidences, as in normal aging with or without vascular risk factors.