Movement disorders in Alzheimer's disease: more rigidity of definitions is needed.

Rigidity, slowness, gait impairment, and other disorders of movement accompany Alzheimer's disease (AD) at various stages of the illness. The presence of these so-called extrapyramidal features have been reported to predict disease prognosis and pathologic localization. Unfortunately, failure to accurately characterize the movement disorder, particularly to distinguish parkinsonism from cortically based motor disturbances (that is, paratonia, apraxia), makes the results of many published studies difficult to interpret. There is an important need to precisely characterize movement disorders in studies of AD to clarify the clinical phenomenology and neurobiology of the condition and to accurately distinguish AD from other degenerative dementias, such as dementia with Lewy bodies.