Transcortical sensory aphasia (TSA) is a kind of aphasia that involves damage to specific areas of the temporal lobe of the brain, resulting in symptoms such as poor auditory comprehension, relatively intact repetition, and fluent speech with semantic paraphasias present. TSA is a fluent aphasia similar to Wernicke's aphasia (receptive aphasia), with the exception of a strong ability to repeat words and phrases. The person may repeat questions rather than answer them ("echolalia"). In all of these ways, TSA is very similar to a more commonly known language disorder, receptive aphasia. However, transcortical sensory aphasia differs from receptive aphasia in that patients still have intact repetition and exhibit echolalia, or the compulsive repetition of words. Transcortical sensory aphasia cannot be diagnosed through brain imaging techniques such as functional magnetic resonance imaging (fMRI), as the results are often difficult to interpret. Therefore, clinicians rely on language assessments and observations to determine if a patient presents with the characteristics of TSA. Patients diagnosed with TSA have shown partial recovery of speech and comprehension after beginning speech therapy. Speech therapy methods for patients with any subtype of aphasia are based on the principles of learning and neuroplasticity. Clinical research on TSA is limited because it occurs so infrequently in patients with aphasia that it is very difficult to perform systematic studies. TSA should not be confused with transcortical motor aphasia (TMA), which is characterized by nonfluent speech output, with good comprehension and repetition. Patients with TMA have impaired writing skills, difficulty speaking and difficulty maintaining a clear thought process. Furthermore, TMA is caused by lesions in cortical motor areas of the brain as well as lesions in the anterior portion of the basal ganglia, and can be seen in patients with expressive aphasia.
Affected brain areas
Transcortical sensory aphasia is caused by lesions in the inferior left temporal lobe of the brain located near Wernicke's area, and is usually due to minor hemorrhage or contusion in the temporal lobe, or infarcts of the left posterior cerebral artery (PCA). One function of the arcuate fasciculus is the connection between Wernicke’s and Broca’s area. In TSA Wernicke’s and Broca’s areas are spared, meaning that lesions do not occur in these regions of the brain. However, since the arcuate fasciculus, Wernicke's area, and Broca's area are secluded from the rest of the brain in TSA, patients still have intact repetition (as information from the arcuate fasciculus is relayed to Broca’s area), but cannot attach meaning to words, either spoken or heard.
Characteristics Transcortical sensory aphasia is characterized as a fluent aphasia. Fluency is determined by direct qualitative observation of the patient’s speech to determine the length of spoken phrases, and is usually characterized by a normal or rapid rate; normal phrase length, rhythm, melody, and articulatory agility; and normal or paragrammatic speech. Transcortical sensory aphasia is a disorder in which there is a discrepancy between phonological processing, which remains intact, and lexical-semantic processing, which is impaired. Therefore, patients can repeat complicated phrases, however they lack comprehension and propositional speech. This disconnect occurs since Wernicke’s area is not damaged in patients with TSA, therefore repetition is spared while comprehension is affected. Patients with intact repetition can repeat both simple and complex phrases spoken by others, e.g. when asked if the patient would like to go for a walk, he or she would respond "go for walk." Although patients can respond appropriately, due to the extent of their TSA, it is most likely that they do not comprehend what others ask them. In addition to problems in comprehension, transcortical sensory aphasia is further characterized based on deficits in naming and paraphasia.
Verbal comprehension Impaired verbal comprehension can be the result a number of causes such as failure of speech sound discrimination, word recognition, auditory working memory, or syntactic structure building. When clinically examined, patients with TSA will exhibit poor comprehension of verbal commands. Based on the extent of the comprehension deficiency, patients will have difficulty following simple commands, e.g. “close your eyes.” Depending on the extent of affected brain area, patients are able to follow simple commands but may not be able to comprehend more difficult, multistep commands, e.g. “point to the ceiling, then touch your left ear with your right hand." Verbal commands as such, that require the patient to cross over the midline of their body are typically more taxing than commands that involve solely the right or left side. When increasing the complexity of verbal commands comprehension is often tested by varying the grammatical structure of the command to determine whether or not the patient understands different grammatical variations of the same sentence. Commands involving the passive voice or possessive, e.g. "If the snake killed the mouse, which one is still alive," usually result in comprehension problems in those who can understand simple questions.
Naming Naming involves the ability to recall an object. Patients with TSA, as well as patients with all other aphasia subtypes, exhibit poor naming. Clinical assessment of naming involves the observer first asking the patient to name high frequency objects such as clock, door, and chair. TSA patients who name common objects with ease generally have difficulty naming both uncommon objects and specific parts of objects such as lapel, or the dial on a watch.
Paraphasia Patients with TSA typically exhibit paraphasia; their speech is fluent but often error-prone. Their speech is often unintelligible as they tend to use the wrong words, e.g. tree instead of train or uses words in senseless and incorrect combinations.
Diagnosis
… excerpt ends here. Continue reading the full article.
