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Higher cerebral functions test neurologic tasks that are thought to reside in the cerebral cortex. Language function defines the dominant hemisphere. The majority of the population is right-handed; for 90% of these patients, the left hemisphere is where language functions reside; hence, they are referred to as left-hemisphere dominant. Even in left-handed patients, most will be left-hemisphere dominant for language. Thus, a large cortical stroke affecting the cortex of the dominant hemisphere (the left hemisphere in most patients, whether they are left- or right-hand dominant) likely will affect language functions.
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The nondominant hemisphere is concerned with spatial relationships. Often a nondominant hemispheric problem is suspected in the ED when the patient has consistent visual inattention to a care provider approaching from one side (usually the left since most patients are left-hemisphere dominant).
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Higher cerebral function pragmatically involves the assessment of language. For a patient with speech that is difficult to understand, a fundamental distinction must be made between dysarthria and a dysphasia (aphasia and dysphasia are often used interchangeably in clinical practice). Dysarthria is a mechanical disorder of speech resulting from difficulty in the production of sound from weakness or incoordination of facial or oral muscles; this may result from a motor system problem (cortical, subcortical, brainstem, cranial nerve, or cerebellar), but it does not represent a disorder of higher cerebral function. Dysphasia is a problem of language resulting from cortical or subcortical damage; the portion of the brain concerned with comprehension, processing, or producing language is impaired.
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There are many different types of aphasias, but a simplified scheme is sufficient for assessment. A description of aphasia into fluent, nonfluent, or mixed patterns is adequate for testing in the ED and for communicating with other physicians.
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Normal conversation monitoring for correct responses is the common screening examination for a language disorder. If suspicion of a language disorder exists, a series of assessments allows confirmation and categorization of the aphasia.
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Test comprehension initially by the ability to follow simple commands. Asking the patient to identify common objects may also be part of the assessment. Use commonly available objects, such as a watch, a pen, or a glass, as a stimulus. Query the patient regarding the names of different parts of the objects. Ask the patient to demonstrate how an object is used. The inability to show how an object is used, assuming hearing and motor functions are intact, may represent an apraxia, defined as the inability to perform a willed act.
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In a nonfluent aphasia (a rough synonym is motor or expressive aphasia), the speed of language and the ability to find the correct words may be impaired. A common type of nonfluent motor aphasia is known as Broca's aphasia. Speech may be halting and slow, with stops between words or word fragments.
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In a fluent aphasia (a rough synonym is auditory or receptive aphasia), the quantity of word production is normal or even increased. Sentences may have normal grammatical structure with normal rhythm, and intonation may be clearly articulated. However, language is impaired, and the listener may be struck by peculiarities of conversation that lack appropriate content. Incorrect words may be substituted within sentences that may be sound-alike words or words with similar yet incorrect meanings. A global or mixed aphasia involves elements of fluent and nonfluent aphasias and is the most common type encountered in clinical practice.
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Nondominant hemisphere problems may show problems of auditory or visual inattention or sensory inattention.
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Testing of mental status and cognitive function requires an appreciation of cultural context and language barriers. Further assessment of comprehension may involve showing the patient a picture (there are some standard stimuli, but almost any magazine photo may be used) and asking for the patient's interpretation of the picture while noting if the content is correctly described and if the sentence structure and word selection of the descriptions are correct.
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Assessing the ability of the patient to repeat a phrase may be a key point in delineating some types of fluent aphasias. Typically, the ability to repeat short words is more impaired than the ability to repeat longer words. A classic test involves the patient repeating the phrase, "No ifs, ands, or buts." In one type of fluent aphasia, Wernicke's aphasia, comprehension is impaired, as is repetition.
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Paraphasic errors may be further characterized in patients with fluent aphasia. A literal paraphasic error is one in which part of a word is replaced by an incorrect sound. The use of spool when spoon is meant is an example of a literal paraphasic error. At times, the errors may reach the point at which the substitutions are not understandable, and a neologism (a meaningless collection of syllables that takes the place of a word in conversation) is produced. Verbal paraphasic errors involve substitution of one correct word for another; for example, a patient may wish to use spoon in a sentence and substitute fork or even bike; the word is a correct word, but the meaning of the sentence is transformed erroneously.2
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A patient aphasic in speaking will also be aphasic in written communication. Writing and drawing simple constructions may be revealing in some patients. A sequence of simple commands such as requesting the patient to draw a circle and then placing numbers like numbers on a clock may reveal constructional errors. A response consistent with dysfunction of the nondominant hemisphere might be numbering half the clock face and stopping or placing all the numbers around one half of the circle.
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Impairment of sensory perception on the cortical level may involve the inability to distinguish objects by touch alone. Implied in this testing is that the primary sensory modalities (sharp, light touch, etc.) are intact. In cases of nondominant hemisphere lesions, the ability to identify objects placed in a hand, such as a coin, may be impaired.
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SPECIAL CIRCUMSTANCES
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Fluent aphasias may so severely impair communication that the patient is thought to be intoxicated or psychotic. Pay attention to the pattern of speaking—this may give the first indication of a language problem, and further constructional or language testing may demonstrate the presence of an aphasia.