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Semantic aphasia

Primary progressive aphasia (PPA) is a language disorder that involves changes in the ability to speak, read, write and understand what others are saying. It is associated with a disease process that causes atrophy in the frontal and temporal areas of the brain, and is distinct from aphasia resulting from a stroke. In 2011 criteria were adopted for the classification of PPA into three clinical subtypes: nonfluent/agrammatic variant PPA, semantic variant PPA and logopenic variant PPA (Gorno-Tempini, Hillis, Weintraub, et. al).

Semantic PPA is a disorder of language in which patients demonstrate a progressive deterioration of understanding words, especially nouns, and recognizing objects while other cognitive faculties remain remarkably spared. Specifically, patients with semantic PPA retain the ability to produce fluent speech, but without being able to generate the key words within sentences, this speech becomes increasing difficult to understand. Semantic PPA patients also lose the ability to recognize the meaning of specific words or to spontaneously name familiar, everyday objects.

Unlike other FTD subtypes, semantic PPA generally does not produce changes in behavior or personality until later stages of the disease. Most people with progressive aphasia maintain the ability to care for themselves, keep up outside interests and, in some instances, remain employed for a few years after onset of the disorder.

Key Clinical Features

  • The hallmark of semantic PPA is difficulty generating or recognizing familiar words. For example, when a patient is shown a picture of a cat, he can neither name it nor can he recognize the word when it is provided. The patient characteristically asks “what is ‘cat’?” when it comes up in conversation or during testing. This happens for rare words first and common nouns for later stages. Verbs and abstract words are surprisingly spared.
  • Fluent spontaneous speech is retained. Especially in early stages, patients may be able to “talk around” the meaning of a specific word they are otherwise unable to generate. In later stages they can repeat their agenda without listening to other speakers. Word-finding pauses in speech become common, and patients have difficulty naming familiar objects.
  • Some patients have problems recognizing familiar objects and faces. The presence of this sign can help confirm the diagnosis.

Neuroimaging studies demonstrate loss of brain volume, blood flow or neural activity in the left temporal lobe of semantic PPA patients. The left side of the brain most frequently manages language function; some left-handed patients may have semantic PPA from right temporal lobe degeneration.

In later stages, clinical features usually include the typical behavioral abnormalities of FTD as described in the Overview to Frontotemporal Degeneration and Behavioral variant FTD.

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