The core and halo of primary progressive aphasia and semantic dementia

Primary progressive aphasia (PPA) is a language-based dementia. It is diagnosed by distinctive clinical features that set it apart from typical forms of Alzheimer’s disease (AD). In contrast to the patient with AD, who usually comes with a history of forgetfulness, the patient with PPA comes with reports of word-finding difficulties, abnormal speech patterns, or a deterioration of spelling. The clinical diagnosis of PPA is made when other mental faculties such as memory for daily events, visuospatial skills, and comportment display no major deficits; when language is the only area of salient and progressive dysfunction for at least the first 2 years of the disease; and when brain imaging does not show a specific lesion, other than atrophy, that can account for the language deficit. Standardized neuropsychological tests of language function are helpful for detecting early stages of the disease. However, a strict reliance on neuropsychological tests, most of which depend on verbal instructions, verbal responses, or covert verbal reasoning, may occasionally lead to the erroneous conclusion that areas other than language are also impaired. Scores on the Mini-Mental Status Examination, for example, can greatly exaggerate the degree of disability. Although the language disorder in PPA may interfere with the ability to memorize word lists or solve reasoning tasks, the patient typically has no difficulty recalling daily events or behaving with sound judgment, indicating that explicit memory, reasoning, and social skills remain relatively intact. PPA is a form of dementia because it causes a gradual cognitive decline to the point at which daily living functions become compromised. It is also an unusual dementia because core memory functions, which are severely impaired in AD, remain largely preserved.