Vascular Dementia
Another common cause of cognitive decline is vascular dementia. Because cerebrovascular disease is common in the elderly (including individuals with Alzheimer disease) differentiating vascular
dementia from other dementias is an important dilemma. The use of diffusion imaging in vascular disease is an important topic in itself and will be explored in greater detail in the next chapter. Patients with vascular dementia and Alzheimer dementia have regional differences of white matter integrity, with selective reduction of FA in the forceps minor (transcallosal fibers through the genu of the corpus callosum in vascular dementia).31
Progressive Supranuclear Palsy
Progressive supranuclear palsy (PSP), although generally manifesting with distinct clinical symptoms, may be confused for Parkinson disease and other conditions, particularly early in the disease process. Therefore, DTI may be helpful in making the diagnosis. In PSP, FA is reduced and MD is increased within the body of the corpus callosum, cingulum, and frontal white matter.32 In another study of PSP, a selected pattern of decreased FA and increased ADC within the inferior fronto-occi- pital fasciculus corresponded to severity of frontal cognitive symptoms and personality change in one study.33 Similarly, a single subject-based DTI study demonstrated that individuals with either cortico- basal degeneration (another Parkinson plus syndrome with prominent motor symptoms) or progressive supranuclear palsy demonstrated widespread FA reductions with an anterior predominance, but did not identify any difference between these two conditions.3 More recent work showed PSP to have a more symmetric and infratentorial pattern of FA reduction when compared to cortico- basal degeneration, despite much overlap (? Fig. 5.10).32 These findings, if validated, could potentially be helpful in distinguishing the two syndromes clinically. One particularly useful conclusion of this study was progression of individuals with nonfluent aphasia to corticobasal degeneration or progressive supranuclear palsy could be predicted by the presence of widespread increased RD and decreased FA on initial DTI examination.3
