Chapter 027. Aphasia, Memory Loss, and Other Focal Cerebral Disorders (Part 5)

Conduction AphasiaSpeech output is fluent but paraphasic, comprehension of spoken language is intact, and repetition is severely impaired. Naming and writing are also impaired. Reading aloud is impaired, but reading comprehension is preserved. The lesion sites spare Brocas and Wernickes areas but may induce a functional disconnection between the two so that lexical representations formed in Wernickes area and adjacent regions cannot be conveyed to Brocas area for assembly into corresponding articulatory patterns. Occasionally, a Wernickes area lesion gives rise to a transient Wernickes aphasia that rapidly resolves into a conduction aphasia. ...
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Chapter 027. Aphasia, Memory Loss, and Other Focal Cerebral Disorders (Part 5) Chapter 027. Aphasia, Memory Loss, and Other Focal Cerebral Disorders (Part 5) Conduction Aphasia Speech output is fluent but paraphasic, comprehension of spoken languageis intact, and repetition is severely impaired. Naming and writing are alsoimpaired. Reading aloud is impaired, but reading comprehension is preserved. Thelesion sites spare Brocas and Wernickes areas but may induce a functionaldisconnection between the two so that lexical representations formed inWernickes area and adjacent regions cannot be conveyed to Brocas area forassembly into corresponding articulatory patterns. Occasionally, a Wernickes arealesion gives rise to a transient Wernickes aphasia that rapidly resolves into aconduction aphasia. The paraphasic output in conduction aphasia interferes withthe ability to express meaning, but this deficit is not nearly as severe as the onedisplayed by patients with Wernickes aphasia. Associated neurologic signs inconduction aphasia vary according to the primary lesion site. Nonfluent Transcortical Aphasia (Transcortical Motor Aphasia) The features are similar to Brocas aphasia, but repetition is intact andagrammatism may be less pronounced. The neurologic examination may beotherwise intact, but a right hemiparesis can also exist. The lesion site disconnects the intact language network from prefrontalareas of the brain and usually involves the anterior watershed zone betweenanterior and middle cerebral artery territories or the supplementary motor cortex inthe territory of the anterior cerebral artery. Fluent Transcortical Aphasia (Transcortical Sensory Aphasia) Clinical features are similar to those of Wernickes aphasia, but repetition isintact. The lesion site disconnects the intact core of the language network fromother temporoparietal association areas. Associated neurologic findings mayinclude hemianopia. Cerebrovascular lesions (e.g., infarctions in the posteriorwatershed zone) or neoplasms that involve the temporoparietal cortex posterior toWernickes area are the most common causes. Isolation Aphasia This rare syndrome represents a combination of the two transcorticalaphasias. Comprehension is severely impaired, and there is no purposeful speechoutput. The patient may parrot fragments of heard conversations (echolalia),indicating that the neural mechanisms for repetition are at least partially intact.This condition represents the pathologic function of the language network when itis isolated from other regions of the brain. Brocas and Wernickes areas tend to bespared, but there is damage to the surrounding frontal, parietal, and temporalcortex. Lesions are patchy and can be associated with anoxia, carbon monoxidepoisoning, or complete watershed zone infarctions. Anomic Aphasia This form of aphasia may be considered the minimal dysfunctionsyndrome of the language network. Articulation, comprehension, and repetitionare intact, but confrontation naming, word finding, and spelling are impaired.Speech is enriched in function words but impoverished in substantive nouns andverbs denoting specific actions. Language output is fluent but paraphasic, circumlocutious, anduninformative. The lesion sites can be anywhere within the left hemispherelanguage network, including the middle and inferior temporal gyri. Anomicaphasia is the single most common language disturbance seen in head trauma,metabolic encephalopathy, and Alzheimers disease. Pure Word Deafness The most common causes are either bilateral or left-sided middle cerebralartery strokes affecting the superior temporal gyrus. The net effect of theunderlying lesion is to interrupt the flow of information from the unimodalauditory association cortex to Wernickes area. Patients have no difficultyunderstanding written language and can express themselves well in spoken orwritten language. They have no difficulty interpreting and reacting to environmental soundssince primary auditory cortex and subcortical auditory relays are intact. Sinceauditory information cannot be conveyed to the language network, however, itcannot be decoded into lexical representations and the patient reacts to speech as ifit were in an alien tongue that cannot be deciphered. Patients cannot repeat spoken language but have no difficulty namingobjects. In time, patients with pure word deafness teach themselves lip reading andmay appear to have improved. There may be no additional neurologic findings, butagitated paranoid reactions are frequent in the acute stages. Cerebrovascularlesions are the most frequent cause.