Cognitive consequences of subcortical magnetic resonance imaging changes in Alzheimer's disease: Comparison to small vessel ischemic vascular dementia

Objective: The objective of this study was to compare psychometric profiles of Alzheimer's disease (AD) patients with subcortical magnetic resonance i maging (MRI) signal abnormalities to those of AD patients without such MRI findings (normal subcortical MRI) and to those of patients with ischemic va scular dementia (IVD) associated with small and primarily subcortical ische mic changes. Background: The cognitive significance of MRI white matter and other subcortical abnormalities in AD is unknown. Prior studies comparing AD patients with white matter changes on MRI have not included IVD patients with comparable MRI findings. If white matter/subcortical changes in AD re flect vascular abnormalities, they might be associated with cognitive profi les similar to those seen in subcortical IVD. Method: We studied 15 AD pati ents with normal subcortical MRIs, 22 AD patients with subcortical MRI hype rintensities, and 18 IVD (NINCDS-ADRDA and NINDS-AIREN criteria) at the Alz heimer's Disease Research Center of the Baylor College of Medicine. IVD pat ients had predominantly small and subcortical signal abnormalities, and non e had large cortical infarcts. AD patients had only nonspecific subcortical signal abnormalities with or without atrophy (atrophy was not analyzed). W e compared the AD group with abnormal MRIs to the AD group with normal subc ortical MRIs and the AD group to the IVD group using ANCOVA planned compari sons (dementia severity and education covaried). Results: AD patients with abnormal MRIs did not differ significantly from AD patients with normal sub cortical MRIs on any of the neuropsychological measures. AD patients exhibi ted significantly better attention/concentration, visuospatial/visuoconstru ctional performance, fetter fluency, motor programming, and simple motor sp eed than IVD patients as well as significantly worse delayed verbal recogni tion memory. Because MRT changes were generally more extensive in IVD, a su bset of AD patients with abnormal subcortical MRIs was compared to a subset of IVD patients matched for degree of MRI signal abnormalities. These subs ets of AD and IVD patients still showed distinctive neuropsychological prof iles. Conclusions: AD patients with or without MRI subcortical signal abnor malities have similar neuropsychological profiles, and they differ from IVD patients with comparable MRI changes. Although MRI signal abnormalities in AD patients who have no history or examination findings of cerebrovascular disease overlap with those seen in IVD patients, they do not seem to have the same cognitive significance. Periventricular hyperintensities (PVHs) an d deep signal hyperintensities, especially those of a mild to moderate degr ee, may reflect a different pathophysiologic process in AD than in IVD and do not necessarily have cognitive consequences in AD patients.