Dementia in Parkinson Disease

Abstract

The possibility that Parkinson disease is associated with dementia has been negated by neurologists for several decades. However, the story is more complex. It should be recalled that predating levodopa therapy, patients could not be formally tested because of bradykinesia and speech difficulties, and this would be a problem particularly in more advanced cases. If cognitive functioning was impaired, this was ascribed to “bradyphrenia” (1), presumably implying a normal mental state, but “slow thinking” as a manifestation of the disease, paralleling bradykinesia. If a patient was frankly disoriented, it would be difficult to be sure to what extent this was a manifestation of drug-induced confusion (2). Other factors could account for pseudodementia, such as social isolation and depression. Finally, if dementia could not be denied it could always be ascribed to a chance association with “senility” or “cerebral arteriosclerosis”. With the introduction of modern drug therapy, however, many of the above factors could be ruled out as contributing to the dementia, or at least could be accounted for. Surprisingly, however, the impression emerged that cognitive changes are common in Parkinson disease.