According to data published in Neurology, tau is associated with a loss in anterior temporal white matter integrity, with early accumulation associated with a decline in white matter. These findings indicate that advanced Alzheimer disease stages may be partly attributable to tau propagation.
Individuals who were cognitively impaired (n=10) and cognitively normal (n=59) were recruited to undergo β-amyloid (Aβ) positron emission tomography (PET), tau PET, diffusion tensor imaging, and magnetic resonance imaging to obtain fractional anisotropy (FA) and mean diffusivity (MD) maps. Individual or composite gray matter seed regions from Aβ, tau, and neurodegeneration were used to create probabilistic white matter summary and individual tracts. The investigators sought to predict FA or MD from corresponding white matter tracts or summaries, using linear regression models for Aβ, age, tau, and white matter hyperintensities (WMH).
The summary PET values in this study were calculated for Aβ (A-summary), tau (T-summary), and neurodegeneration (N-summary) regions. Age and WMH were found to be significant predictors of white matter integrity for the projections from A- and N-summary tracts (all P <.001). In addition, age, WMH, and tau predicted MD for projections from T-summary tracts. The investigators did not find a predictive value of amyloid for MD or FA in any of the summary tracts. Tau was found to be a significant predictor of MD in the anterior temporal white matter.
A small sample size and the inability to “dissociate WM dysfunction independently of gray matter atrophy” represented the key study limitations, as reported by the investigators.
On the basis of these findings, metrics of diffusion tensor imaging “may provide an important biomarker for predicting and monitoring tau progression in symptomatic AD.”
Strain JF, Smith RX, Beaumont H, et al. Loss of white matter integrity reflects tau accumulation in Alzheimer disease defined regions [published online June 29, 2018]. Neurology. doi: 10.1212/WNL.0000000000005864