Aphasia is an acquired disorder of language that is frequently observed in patients with lesions in the left hemisphere. Stroke is one of the most common causes of aphasia; slowly progressive aphasia may be seen with mass lesions, or with neurodegenerative diseases such as primary progressive aphasia. Symptoms of aphasia, which may be observed individually or in different combinations, include poor word retrieval (anomia), difficulty accessing meaning from spoken language (comprehension deficits), and inability to repeat words, phrases or sentences or to apply the grammatical and syntactic rules to understand or generate language.
When evaluating a patient with suspected aphasia, the following parameters should be assessed. First, naming should be tested by asking subjects to name objects that differ in frequency from high to low (e.g., thumb vs. eyebrow) and length (e.g., bat vs. propeller). The nature of the errors should be noted. Patients will frequently be unable to generate a response or produce a sound-based error; less commonly, patients may substitute a word that is similar in meaning. Fluency should be assessed by noting the rate and ease with which language is produced. Non-fluent patients may generate only a few words at a time whereas fluent patients may produce long phrases or even sentences. Comprehension should be tested by asking patients to perform simple tasks ranging in complexity from simple commands (e.g., “close your eyes”) to complex, sequential actions that require grammatical competence (e.g., “After you point to the ceiling, point to the door with your left thumb.”). Repetition should be assessed by asking patients to repeat utterances that vary across the dimensions of frequency and length; for example, patients may be asked to repeat single, high-frequency words (e.g., dog) to more complex utterances with multiple, low-frequency words (e.g., “The seamstress stitched the wedding gown.”). Finally, it is important to have a large sample of language to evaluate; to that end, it is often useful to ask patients to tell a story or elaborate on topics of particular interest to them.
A number of distinct types of aphasia have traditionally been described. Although not all investigators agree that aphasia subtypes are readily distinguished or consistent across patients, they have a venerable history and are clinically useful.
Anomic aphasia, the most common type of aphasia, is characterized by difficulty naming objects and concepts with relatively preserved comprehension, fluency, and repetition. It may be caused by lesions anywhere in the left hemisphere but is most frequently observed as a residual effect of more severe aphasias.
Conduction aphasia is characterized by impaired repetition and naming but relatively preserved fluency and comprehension. Traditionally it is attributed to lesions of white matter tracts connecting Wernicke and Broca areas, but it is most frequently observed as the residual manifestation of Wernicke aphasia.
Transcortical aphasias are characterized by intact repetition with impairments in other language faculties. Transcortical motor and sensory aphasia are associated with deficits in fluency and comprehension, respectively. Mixed transcortical aphasia is associated with impaired comprehension and poor fluency. In these disorders perisylvian tissue, including white matter tracts, is preserved; lesions are often subcortical.
Wernicke aphasia ( Fig. 5.1 ) is characterized by fluent speech with impaired comprehension, repetition, and naming. It is associated with lesions involving the posterior portion of the superior temporal gyrus.