Pathologic Correlates of Apraxia in Alzheimer Disease

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Abstract
ALTHOUGH THERE have been many studies1-9 on clinicopathologic correlations in Alzheimer disease (AD), few attempts have been made to determine whether the distribution of AD lesions is related to cognitive deficits that can be localized to specific brain regions.10,11 Apraxia is a good candidate for these types of studies since investigations of focal pathology have suggested that this condition is associated with both structural and functional abnormalities in restricted cortical areas.12-23 Apraxia is defined as a disorder of skilled movements that cannot be explained by palsy, paresis, ataxia, akinesia, posture, tone or movement disorders, comprehension impairment, or deafferentation. Three of the main forms of apraxia are ideomotor, dressing, and constructional apraxia.11,20,21 Ideomotor apraxia represents a difficulty in making gestures caused by an inability to translate the concept of a motor sequence into the corresponding motor action. In the artificial context of testing, patients are unable to select, sequence, and orient spatially meaningful transitive and intransitive and meaningless movements. Bilateral injuries of the parietal lobes as well as the anterior segment of the corpus callosum have been related to ideomotor apraxia.14,16,18-20,22-25 Dressing apraxia represents a particular form of apraxia confined to clothing use and is often associated with focal lesions in the right parietal lobe.15,17 Constructional apraxia refers to a visuospatial disorder characterized by an impairment in the spatial organization required when parts of objects are assembled to form a single entity. It is thought to be related to the parietal-occipital cortex pathology15,17,26-31; however, this view has been challenged.11,32