Language disorders affect the ability to comprehend and express spoken or written language, or both. Aphasias are the most classic syndromes and are presented here; disorders of written language, including alexias and agraphias as well as other related language disorders, are discussed in the next section.
The clinical characteristics of aphasia syndromes are summarized in Ta.b.le.,..§:4 . PERISYLVIAN SYNDROMES
Perisylvian syndromes include classic aphasic syndromes occurring with lesions along the sylvian fissure. They include Broca's, Wernicke's, and conduction aphasia syndromes. Subtypes of Broca's and Wernicke's aphasia are described ( Fig 6-4 ).
Broca's Aphasia. In 1861 Paul Broca described an aphasic syndrome and correlated it with underlying pathology. '29] Broca's aphasia has since been called by several names. For instance, the same findings have been called expressive aphasia, anterior aphasia, and motor aphasia. The term Broca's aphasia is still the most universally recognized for this syndrome, and a specified anatomical localization has been widely accepted.
Verbal output in Broca's aphasia, which is assessed through conversational speech, is markedly reduced, often to fewer than 10 words per minute. The central feature of Broca's aphasia is a nonfluent verbal output y ; it is sparse, poorly articulated, and produced with considerable effort. The quality of speech is markedly dysprosodic, lacking melody and rhythm. Sentences are very short, and most responses by a nonfluent aphasic are limited to single word sentences or telegraphic speech.y Even though very few words are produced by the nonfluent aphasic, the output often conveys significant information and may be well inflected.
Figure 6-4 Lateral view of the left hemisphere indicating presylvian area (central clear region), and extrasylvian areas or border zone area (cross-hatched region). TMA = region where a lesion may result in transcortical motor aphasia; TSA = region where a lesion may result in transcortical sensory aphasia.
There is near absence of syntactical words (prepositions, articles, adverbs). The words produced are usually nouns, action verbs, or descriptive adjectives. This alteration of normal grammatical sentence structure is called agrammatism. y
Other language characteristics are less dramatic. The comprehension of spoken language is always significantly better than verbal output. Most patients with Broca's aphasia have some degree of comprehension defect; most often it is a difficulty understanding syntactical structures. The disturbance involves abnormal comprehension of the same terms that the patients omit from their verbal expressions, and they have difficulty with relational words such as up and down, and inside and outside. Repetition of spoken language is abnormal. Confrontation naming is invariably poor. Patients often accept prompting well and improve in pronunciation or initiating articulation. This finding is characteristic of Broca's aphasia, even though it can be found in other types of aphasia. Reading out loud is very difficult for Broca's aphasia patients. Reading comprehension can also be somewhat disturbed, but it is comparatively well preserved. Writing is abnormal, affecting both writing to command or copying written material. The letters are oversized, and multiple misspellings are common.
Neurological examination shows some degree of right-sided weakness in the majority of patients (over 80 percent) with a variable degree of severity. The weakness usually has a brachiofacial distribution. Hyperactive reflexes are frequently present on the involved side. Ideomotor apraxia, an inability to carry out on command a task that can be done spontaneously, frequently involves the nonpathological left hand of patients with Broca's aphasia. y
Sensory loss is not consistent. If a severe hemisensory loss is present at the onset but clears rapidly, a unilateral inattention syndrome is suggested rather than a true sensory defect.y Often, a conjugate ocular deviation to the left will be present initially. A visual field defect is uncommon and, if it is present, suggests more posterior neuroanatomical involvement.
The site of pathology in Broca's aphasia has been localized to the left posteroinferior frontal lobe, Brodmann's area 44, or simply Broca's area. Patients with the classic syndrome of Broca's aphasia often have associated deep-extending pathology involving the insula, basal ganglia, and periventricular white matter ( „„Fig.^6-5 ).y , y , y , '34] Various types of pathology, including trauma, tumor, infection, abcess, and others, can produce Broca's aphasia. The most common cause is cerebral vascular disease. Occlusion of one or several tributaries of the middle cerebral artery feeding the inferior frontal region is the most common cause of Broca's aphasia.
Broca's aphasia that rapidly improves is associated with
Figure 6-5 MRI of the brain showing a large, deep infarct involving Broca's area, the internal capsule and the basal ganfFrom Damasio H, Damasio AR: Lesion Analysis in Neuropsychology. New York, Oxford University Press, 1989.)
lesions involving the frontal operculum but not extending deeply. These patients have a different clinical picture, and the condition has been called Little Broca's aphasia or aphemia.y
Wernicke's Aphasia. In 1874, Karl Wernicke described a language impairment that was characterized by fluent verbal output and impaired comprehension. Essentially identical aphasia syndromes have also been called sensory aphasia or receptive aphasia.
Verbal output in Wernicke's aphasia is either normal or increased (over 200 words per minute). y Speech production demands little or no effort, and articulation is normal. Sentences are of normal length with normal prosody. However, sentences are devoid of meaningful words, so that almost no information is conveyed, an output that can be called empty speech; paraphasia is common. y Paraphasia may be literal when a syllable is substituted within a word (phonemic substitution) or semantic (also termed verbal paraphasia) when a word is substituted. Words can also be substituted by meaningless, nonsense words (neologisms). "Jargon aphasia" is a severe form of Wernicke's aphasia with rapid verbal output, abundant paraphasic substitutions, and incomprehensible verbalization. When patients have an increased output and speak incessantly, this is called logorrhea or pressured speech, an aphasic output nearly diagnostic of Wernicke's aphasia.
Comprehension of spoken language is disturbed in Wernicke's aphasia. The severity of the comprehension deficit is variable. Patients can sometimes understand a few words and even short sentences. Comprehension ability may decrease with testing, a phenomenon called fatigue or jamming. Two varieties of comprehension defect are described.y In one variety, the ability to comprehend spoken language is considerably worse than the ability to comprehend written language (the patient is predominantly word deaf), whereas in the other the opposite is true (the patient is predominantly word blind). Classic Wernicke's aphasia features a combination of the two.[i7]
Other aspects of language are disturbed. Repetition of spoken language is invariably abnormal. Naming is often abnormal, and grossly paraphasic responses can be produced during confrontational naming. Reading out loud as well as reading comprehension are abnormal. Writing is also abnormal in Wernicke's aphasia. The output consists of well-formed letters combined in a meaningless manner. Correctly produced words may be scattered among the unintelligible combinations.
Neurological examination is often unrevealing. Some degree of cortical sensory loss may be present. A superior quadrantanopia suggesting involvement of the temporal radiation of the geniculocalcarine tract is often the only neurological deficit associated with Wernicke's aphasia. The absence of associated neurological deficits may lead to the erroneous diagnosis of psychosis or schizophrenia, particularly in younger patients, or dementia in older patients.
The pathology in most cases of Wernicke's aphasia is localized in the auditory association cortex of the posterosuperior portion of the first temporal gyrus of the left temporal lobe. When word deafness is predominant over word blindness, pathology tends to be deeper in the first temporal gyrus, involving Heschl's gyrus or its connections. Predominance of word blindness suggests greater involvement of the contiguous parietal cortex (primarily the angular gyrus). Pure word deafness is discussed in the next section. A variety of pathological entities are known to produce Wernicke's aphasia, including vascular events and tumors or abscesses of the temporal lobe.
The outcome and recovery of Wernicke's aphasia is less favorable than Broca's aphasia. With improvement, some ability to recognize spoken words appears. With continued improvement the patient may be able to understand auditory material if it is presented slowly. y Recovery may be delayed by associated behavioral problems; most of the patients, however, are unaware of their deficit, making rehabilitation efforts difficult, and paranoid ideation common. y
Conduction Aphasia. Conduction aphasia occurs in up to 15 percent of admissions of patients with aphasia in some reports. y , y The defining feature of conduction aphasia is the repetition difficulty. Unlike Broca's aphasia, verbal output in conduction aphasia is fluent and paraphasic, but the amount of output is less than Wernicke's aphasia. Articulation is excellent, and comprehension of spoken language is intact. In contrast, the repetition of numbers or the naming of colors may be contaminated with verbal paraphasias. Confrontational naming is also disturbed mainly because of paraphasic contamination. Reading out loud rapidly breaks down into a severely paraphasic output; in contrast, reading silently for comprehension is intact. The ability to write is invariably disturbed to some extent. Most often, words and letters are substituted or misspelled or misplaced. Often, conduction aphasia is not diagnosed at the onset but develops in the recovery phase from Wernicke's aphasia. With further improvement, patients remain anomic.
The neurological examination often shows no abnormalities, but variable motor or sensory findings and ideomotor apraxia may be present, particularly with lesions above the sylvian fissure. A pseudothalamic pain syndrome may develop in the recovery phase. Visual fields may show variable deficits reflecting involvement of different sites neighboring the locus of pathology underlying conduction aphasia. y
The site of pathology in conduction aphasia involves the left hemisphere arcuate fasciculus, most often deep to the supramarginal gyrus. This may produce a separation of the sensory and motor language areas, as originally suggested by Wernicke. y , y Cases with features of conduction aphasia have been described with lesions outside this area, notably in the left supramarginal gyrus and left temporal gyrus. y , y The most common cause of conduction aphasia is occlusion of a portion of the angular branch of the middle cerebral artery.
Global Aphasia. In global aphasia, all language functions are seriously impaired. The verbal output is always limited but not to a state of mutism. Single words or syllables can sometimes be produced, and occasionally, verbal output is limited to strings of a single syllable. y Comprehension is often better than verbal output but is also seriously disturbed. Repetition, naming, reading, and writing are all compromised. Neurological examination often shows hemiplegia, visual field loss, and sensory abnormalities. In some patients, the condition evolves from global aphasia to the other aphasia syndromes. Patients
who do not make a rapid recovery soon after onset have a poor prognosis. The pathology may involve a large part of the left hemisphere, often in the distribution of the middle cerebral artery. Rare cases are reported, however, with a global aphasia but few associated neurological deficits. In those cases, small, strategically placed lesions involve Broca's and Wernicke's areas simultaneously. y Strokes are probably the most common cause, but a tumor, trauma, an infection, a gunshot wound, and other causes can all lead to severe global aphasia.
In extrasylvian aphasias, pathology is localized outside the regions immediately bordering the sylvian fissure (see Fig 6.-4 ). There are four recognized aphasic syndromes in this category. Transcortical motor, transcortical sensory, mixed transcortical aphasias, and supplementary motor area aphasia are discussed.
Transcortical Motor Aphasia. Transcortical motor aphasia resembles Broca's aphasia, but the patients are able to repeat. The term transcortical aphasia was suggested by Wernicke in 1881 and Lichtheim in 1885. It was also termed anterior isolation syndrome by Benson and Geschwind. y Verbal output is described as nonfluent and dysarthric, as in Broca's aphasia. But patients with transcortical motor aphasia have a stronger tendency to stutter, and output is often agrammatic and is produced with considerable effort. Comprehension of spoken language is normal. Sometimes the presence of associated apraxia might falsely suggest that the patient does not comprehend when asked to point to room objects or carry out commands. Repetition is usually good to excellent. Confrontational naming is often disturbed, and prompting with contextual cues or phonemic cues helps these patients considerably. Reading out loud produces poorly articulated speech. Comprehension of written language is intact and usually better than in patients with Broca's aphasia. Writing ability is always defective. It is often clumsily written with large letters, poor spelling, and agrammatical output. Most often, transcortical motor aphasia is seen in the recovery phase from Broca's aphasia. Patients with transcortical motor aphasia usually have variable recovery.
Neurological examination usually reveals right hemiplegia. Apraxia is very common, and conjugate ocular deviation is occasionally seen. Sensory loss and visual field loss do not occur.
Transcortical motor aphasia is not a frequent entity. Cases occur with lesions in the anterior watershed area or with occlusion of the left anterior cerebral artery. In some cases, pathology is located in the left frontal or prefrontal regions of the dominant hemisphere anterior or superior to Broca's area. y It is suggested that transcortical motor aphasia is the result of a separation of the pathways that connect the supplementary motor area with Broca's area. y Other patients have lesions of the left medial frontal region.
A variant of transcortical motor aphasia has been termed supplementary motor area aphasia. This syndrome is basically identical to transcortical motor aphasia but is produced by damage to the dominant hemisphere medial frontal structures notably the cingulate cortex and supplementary motor area. Following initial mutism, patients with this disturbance develop a slow hypophonic output that improves considerably with repetition. In comparison with transcortical motor aphasia, patients with supplementary motor area aphasia have a characteristic neurological disturbance with weakness of the right lower extremity and shoulder but relatively normal strength in the arm and face. A similar pattern of sensory disturbance may or may not be present. [?i This syndrome is not common and occurs most often after occlusion of the dominant hemisphere anterior cerebral artery.
Transcortical Sensory Aphasia. Transcortical sensory aphasia is a distinct entity that features fluent output that is often contaminated by considerable paraphasia, including both neologistic and semantic substitutions. Comprehension of spoken language is severely disturbed. In striking contrast, repetition is intact. The patient is often echolalic, repeating most of the examiner's utterances with apparent unawareness of what is said. Naming is disturbed. Reading out loud may be preserved but is usually contaminated with paraphasic errors. Reading comprehension is defective. Writing is also abnormal.
Sensory abnormalities usually of the cortical type are found as well as a visual field defect. Occasionally, patients with transcortical sensory aphasia have a normal neurological examination and are misdiagnosed as schizophrenics.
The pathology underlying this syndrome is often located in the parietal and temporal areas, posterior to the perisylvian region. Occlusion of the left internal carotid with a subsequent posterior border zone infarction frequently underlies transcortical sensory aphasia. Tumors in the parieto-temporo-occipital junction area, as well as trauma, intracerebral hematoma,y and degenerative disorders such as Alzheimer's disease y are other reported causes.
Transcortical sensory aphasia may also follow the resolution of Wernicke's aphasia. The prognosis is usually guarded.
Mixed Transcortical Aphasia. Mixed transcortical aphasia, or isolation aphasia, is equivalent to global aphasia with preserved repetition. y Patients with this syndrome do not speak unless spoken to and their verbal output is almost entirely limited to what has been offered by the examiner, a true echolalia. y Patients may also embellish the output in the form of the completion phenomenon. Thus, if told the beginning of a common phrase, the patient may not only repeat what has been said but continue the phrase to completion. Comprehension of spoken language is severely disturbed. The ability to repeat, although well preserved compared with all other language features, remains limited and is often below normal. The number of words in a sentence that can be repeated is often limited to three or four. Naming, reading out loud, reading for comprehension, and writing are severely compromised. When a response is elicited, it is often contaminated with paraphasias. Neurological examination reveals variable motor, sensory, and visual field deficits.
The pathology underlying mixed transcortical aphasia is most often located in both the anterior and posterior vascular border zone cortical areas of the left hemisphere. Although border zone pathology is rare in its pure form, individuals with acute left internal carotid occlusion or the residuals of severe cerebral edema or prolonged hypoxia may show the mixed transcortical language pattern. The
course of this syndrome is often stable but unimproving. The syndrome has also been seen with unusual frequency in Creutzfeldt-Jakob disease. SUBCORTICAL APHASIA
With the advent of brain imaging, language disorders that previously were difficult to characterize were found to have pathology affecting subcortical structures, particularly the basal ganglia and the thalamus. y Considerable variation is seen in the clinical picture depending on the specific subcortical structures involved, but several general characteristics help define the entity. First, there is typically an acute onset with mutism, recovering slowly to a hypophonic, slow, and poorly articulated output. In addition, other language features vary depending on the site of subcortical pathology.
There are several potential localizations for subcortical aphasia. Left thalamic lesions most commonly secondary to hypertensive hemorrhage have a Wernicke-like fluent aphasia, with paraphasic output but with comparatively good comprehension and repetition. y Causes of thalamic aphasia include hemorrhage and ischemic infarctions. Left striatal lesions often produce dysarthria, nonfluent paraphasic speech, and relatively mild comprehension deficits, as well as preserved repetition. These findings resemble the transcortical motor aphasia except for the presence of paraphasias and dysarthria. More posterior lesions occasionally produce a Wernicke-like aphasia. Even small lesions in the posterior internal capsule and adjacent putamen occasionally produce mild, mixed aphasic syndromes, but they usually manifest dysarthria.
Research focusing on subcortical aphasias is an evolving field of knowledge, and new clinical syndromes with more precise anatomical localization are being described. There is a high likelihood of recovery from subcortical aphasia, and this transient nature can be accepted as a diagnostic characteristic. y If, however, the causative lesion also involves language cortex, which is a common situation, recovery will be incomplete. y It has been suggested from PET studies that lesions in the basal ganglia affect language functions indirectly via decreased activation of the language cortex. y The presentation of a difficult-to-classify aphasic syndrome, in the presence of dysarthria and right hemiparesis, should lead to suspicion of a subcortical lesion.
Anomic Aphasia. Anomic aphasia is also known as amnestic aphasia and nominal aphasia. Anomia is a very frequent finding in aphasia to the extent that it is considered imprudent to suggest a diagnosis of aphasia in its absence. y Anomic aphasia refers to those aphasic syndromes in which the principal deficit is in confrontational naming. Although spontaneous speech is fluent and easily produced, there is an emptiness, which results from a lack of substantive words, with substitution of many nonspecific words that often fail to communicate an idea satisfactorily. This vague output is called empty speech. Most often, excessive word-finding pauses typify the anomic output. If the description demands a substantive word that cannot be produced, another description may be tried. This rapidly produces a circuitous output called circumlocution.
Other language aspects are more intact. Comprehension is relatively well preserved. Reading and writing may be entirely normal but not infrequently there is abnormality in both. When anomia occurs by itself, it may result from pathology almost anywhere in the left hemisphere area and can even be seen in some cases of right hemisphere lesions.y , y There is a fairly common syndrome in which anomic aphasia is associated with alexia plus the Gerstmann's syndrome (agraphia, right-left disorientation, acalculia, and finger agnosia). In this syndrome, the pathology is localized in the left angular gyrus. y , y Anomia is often the residual of more severe aphasic syndromes and remains the complaint of many well-recovered aphasics. Anomia is also seen in degenerative disorders such as Alzheimer's disease.
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