The areas that are critical for language make up a distributed network located along the perisylvian region of the left hemisphere. One hub, located in the inferior frontal gyrus, is known as Broca’s area. Damage to this region impairs phonology, fluency, and the grammatical structure of sentences. The location of a second hub, known as Wernicke’s area, is less clearly settled but is traditionally thought to include the posterior parts of the temporal lobe. Cerebrovascular accidents that damage this area interfere with the ability to understand spoken or written sentences as well as the ability to express thoughts through meaningful words and statements. These two hubs are interconnected with each other and with surrounding parts of the frontal, parietal, and temporal lobes. Damage to this network gives rise to language impairments known as aphasia. Aphasia should be diagnosed only when there are deficits in the formal aspects of language, such as word finding, word choice, comprehension, spelling, or grammar. Dysarthria and mutism do not by themselves lead to a diagnosis of aphasia. In approximately 90% of right-handers and 60% of left-handers, aphasia occurs only after lesions of the left hemisphere.
The clinical examination of language should include the assessment of naming, spontaneous speech, comprehension, repetition, reading, and writing. A deficit of naming (anomia) is the single most common finding in aphasic patients. When asked to name a common object, the patient may fail to come up with the appropriate word, may provide a circumlocutious description of the object (“the thing for writing”), or may come up with the wrong word (paraphasia). If the patient offers an incorrect but related word (“pen” for “pencil”), the naming error is known as a semantic paraphasia; if the word approximates the correct answer but is phonetically inaccurate (“plentil” for “pencil”), it is known as a phonemic paraphasia. In most anomias, the patient cannot retrieve the appropriate name when shown an object but can point to the appropriate object when the name is provided by the examiner. This is known as a one-way (or retrieval-based) naming deficit. A two-way (comprehension-based) naming deficit exists if the patient can neither provide nor recognize the correct name. Spontaneous speech is described as “fluent” if it maintains appropriate output volume, phrase length, and melody or as “nonfluent” if it is sparse and halting and average utterance length is below four words. The examiner also should note the integrity of grammar as manifested by word order (syntax), tenses, suffixes, prefixes, plurals, and possessives. Comprehension can be tested by assessing the patient’s ability to follow conversation, asking yes-no questions (“Can a dog fly?” “Does it snow in summer?”), asking the patient to point to appropriate objects (“Where is the source of illumination in this room?”), or asking for verbal definitions of single words. Repetition is assessed by asking the patient to repeat single words, short sentences, or strings of words such as “No ifs, ands, or buts.” The testing of repetition with tongue twisters such as “hippopotamus” and “Irish constabulary” provides a better assessment of dysarthria and palilalia than of aphasia. It is important to make sure that the number of words does not exceed the patient’s attention span. Otherwise, the failure of repetition becomes a reflection of the narrowed attention span (working memory) rather than an indication of an aphasic deficit. Reading should be assessed for deficits in reading aloud as well as comprehension. Alexia describes an inability to either read aloud or comprehend single words and simple sentences; agraphia (or dysgraphia) is used to describe an acquired deficit in spelling.
Aphasias can arise acutely in cerebrovascular accidents (CVAs) or gradually in neurodegenerative diseases. The syndromes listed in Table 22-1 are most applicable to the former group, where gray matter and white matter at the lesion site are abruptly and jointly destroyed. Progressive neurodegenerative diseases can have cellular, laminar, and regional specificity, giving rise to a different set of aphasias that will be described separately. The syndromes outlined below are idealizations and rarely occur in pure form.
TABLE 22-1CLINICAL FEATURES OF APHASIAS AND RELATED CONDITIONS COMMONLY SEEN IN CEREBROVASCULAR ACCIDENTS ||Download (.pdf) TABLE 22-1CLINICAL FEATURES OF APHASIAS AND RELATED CONDITIONS COMMONLY SEEN IN CEREBROVASCULAR ACCIDENTS
| ||COMPREHENSION ||REPETITION OF SPOKEN LANGUAGE ||NAMING ||FLUENCY |
|Wernicke’s ||Impaired ||Impaired ||Impaired ||Preserved or increased |
|Broca’s ||Preserved (except grammar) ||Impaired ||Impaired ||Decreased |
|Global ||Impaired ||Impaired ||Impaired ||Decreased |
|Conduction ||Preserved ||Impaired ||Impaired ||Preserved |
|Nonfluent (anterior) transcortical ||Preserved ||Preserved ||Impaired ||Impaired |
|Fluent (posterior) transcortical ||Impaired ||Preserved ||Impaired ||Preserved |
|Isolation ||Impaired ||Echolalia ||Impaired ||No purposeful speech |
|Anomic ||Preserved ||Preserved ||Impaired ||Preserved except for word-finding pauses |
|Pure word deafness ||Impaired only for spoken language ||Impaired ||Preserved ||Preserved |
|Pure alexia ||Impaired only for reading ||Preserved ||Preserved ||Preserved |
Comprehension is impaired for spoken and written words and sentences. Language output is fluent but is highly paraphasic and circumlocutious. Paraphasic errors may lead to strings of neologisms, which lead to “jargon aphasia.” Speech contains few substantive nouns. The output is therefore voluminous but uninformative. For example, a patient attempts to describe how his wife accidentally threw away something important, perhaps his dentures: “We don’t need it anymore, she says. And with it when that was downstairs was my teeth-tick … a … den … dentith … my dentist. And they happened to be in that bag … see? …Where my two … two little pieces of dentist that I use … that I … all gone. If she throws the whole thing away … visit some friends of hers and she can’t throw them away.”
Gestures and pantomime do not improve communication. The patient may not realize that his or her language is incomprehensible and may appear angry and impatient when the examiner fails to decipher the meaning of a severely paraphasic statement. In some patients this type of aphasia can be associated with severe agitation and paranoia. The ability to follow commands aimed at axial musculature may be preserved. The dissociation between the failure to understand simple questions (“What is your name?”) in a patient who rapidly closes his or her eyes, sits up, or rolls over when asked to do so is characteristic of Wernicke’s aphasia and helps differentiate it from deafness, psychiatric disease, or malingering. Patients with Wernicke’s aphasia cannot express their thoughts in meaning-appropriate words and cannot decode the meaning of words in any modality of input. This aphasia therefore has expressive as well as receptive components. Repetition, naming, reading, and writing also are impaired.
The lesion site most commonly associated with Wernicke’s aphasia is the posterior portion of the language network. An embolus to the inferior division of the middle cerebral artery, to the posterior temporal or angular branches in particular, is the most common etiology (Chap. 32). Intracerebral hemorrhage, head trauma, and neoplasm are other causes of Wernicke’s aphasia. A coexisting right hemianopia or superior quadrantanopia is common, and mild right nasolabial flattening may be found, but otherwise, the examination is often unrevealing. The paraphasic, neologistic speech in an agitated patient with an otherwise unremarkable neurologic examination may lead to the suspicion of a primary psychiatric disorder such as schizophrenia or mania, but the other components characteristic of acquired aphasia and the absence of prior psychiatric disease usually settle the issue. Prognosis for recovery of language function is guarded.
Speech is nonfluent, labored, interrupted by many word-finding pauses, and usually dysarthric. It is impoverished in function words but enriched in meaning-appropriate nouns. Abnormal word order and the inappropriate deployment of bound morphemes (word endings used to denote tenses, possessives, or plurals) lead to a characteristic agrammatism. Speech is telegraphic and pithy but quite informative. In the following passage, a patient with Broca’s aphasia describes his medical history: “I see … the dotor, dotor sent me … Bosson. Go to hospital. Dotor … kept me beside. Two, tee days, doctor send me home.”
Output may be reduced to a grunt or single word (“yes” or “no”), which is emitted with different intonations in an attempt to express approval or disapproval. In addition to fluency, naming and repetition are impaired. Comprehension of spoken language is intact except for syntactically difficult sentences with a passive voice structure or embedded clauses, indicating that Broca’s aphasia is not just an “expressive” or “motor” disorder and that it also may involve a comprehension deficit in decoding syntax. Patients with Broca’s aphasia can be tearful, easily frustrated, and profoundly depressed. Insight into their condition is preserved, in contrast to Wernicke’s aphasia. Even when spontaneous speech is severely dysarthric, the patient may be able to display a relatively normal articulation of words when singing. This dissociation has been used to develop specific therapeutic approaches (melodic intonation therapy) for Broca’s aphasia. Additional neurologic deficits include right facial weakness, hemiparesis or hemiplegia, and a buccofacial apraxia characterized by an inability to carry out motor commands involving oropharyngeal and facial musculature (e.g., patients are unable to demonstrate how to blow out a match or suck through a straw). The cause is most often infarction of Broca’s area (the inferior frontal convolution; “B” in Fig. 22-1) and surrounding anterior perisylvian and insular cortex due to occlusion of the superior division of the middle cerebral artery (Chap. 32). Mass lesions, including tumor, intracerebral hemorrhage, and abscess, also may be responsible. When the cause of Broca’s aphasia is stroke, recovery of language function generally peaks within 2 to 6 months, after which time further progress is limited. Speech therapy is more successful than in Wernicke’s aphasia.
Speech output is fluent but contains many phonemic paraphasias, comprehension of spoken language is intact, and repetition is severely impaired. Naming elicits phonemic paraphasias, and spelling is impaired. Reading aloud is impaired, but reading comprehension is preserved. The lesion sites spare the functionality of Broca’s and Wernicke’s areas but may induce a disconnection between the two. Occasionally, a transient Wernicke’s aphasia may rapidly resolve into a conduction aphasia. The paraphasic output in conduction aphasia interferes with the ability to express meaning, but this deficit is not nearly as severe as the one displayed by patients with Wernicke’s aphasia. Associated neurologic signs in conduction aphasia vary according to the primary lesion site.
Transcortical aphasias: fluent and nonfluent
Clinical features of fluent (posterior) transcortical aphasia are similar to those of Wernicke’s aphasia, but repetition is intact. The lesion site disconnects the intact core of the language network from other temporoparietal association areas. Associated neurologic findings may include hemianopia. Cerebrovascular lesions (e.g., infarctions in the posterior watershed zone) and neoplasms that involve the temporoparietal cortex posterior to Wernicke’s area are common causes. The features of nonfluent (anterior) transcortical aphasia are similar to those of Broca’s aphasia, but repetition is intact and agrammatism is less pronounced. The neurologic examination may be otherwise intact, but a right hemiparesis also can exist. The lesion site disconnects the intact language network from prefrontal areas of the brain and usually involves the anterior watershed zone between anterior and middle cerebral artery territories or the supplementary motor cortex in the territory of the anterior cerebral artery.
Global and isolation aphasias
Global aphasia represents the combined dysfunction of Broca’s and Wernicke’s areas and usually results from strokes that involve the entire middle cerebral artery distribution in the left hemisphere. Speech output is nonfluent, and comprehension of language is severely impaired. Related signs include right hemiplegia, hemisensory loss, and homonymous hemianopia. Isolation aphasia represents a combination of the two transcortical aphasias. Comprehension is severely impaired, and there is no purposeful speech output. 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 it is isolated from other regions of the brain. Broca’s and Wernicke’s areas tend to be spared, but there is damage to the surrounding frontal, parietal, and temporal cortex. Lesions are patchy and can be associated with anoxia, carbon monoxide poisoning, or complete watershed zone infarctions.
This form of aphasia may be considered the “minimal dysfunction” syndrome of the language network. Articulation, comprehension, and repetition are intact, but confrontation naming, word finding, and spelling are impaired. Word-finding pauses are uncommon, so language output is fluent but paraphasic, circumlocutious, and uninformative. The lesion sites can be anywhere within the left hemisphere language network, including the middle and inferior temporal gyri. Anomic aphasia is the single most common language disturbance seen in head trauma, metabolic encephalopathy, and Alzheimer’s disease.
The most common causes are either bilateral or left-sided middle cerebral artery (MCA) strokes affecting the superior temporal gyrus. The net effect of the underlying lesion is to interrupt the flow of information from the auditory association cortex to the language network. Patients have no difficulty understanding written language and can express themselves well in spoken or written language. They have no difficulty interpreting and reacting to environmental sounds since primary auditory cortex and auditory association areas of the right hemisphere are spared. Because auditory information cannot be conveyed to the language network, however, it cannot be decoded into neural word representations, and the patient reacts to speech as if it were in an alien tongue that cannot be deciphered. Patients cannot repeat spoken language but have no difficulty naming objects. In time, patients with pure word deafness teach themselves lipreading and may appear to have improved. There may be no additional neurologic findings, but agitated paranoid reactions are common in the acute stages. Cerebrovascular lesions are the most common cause.
Pure alexia without agraphia
This is the visual equivalent of pure word deafness. The lesions (usually a combination of damage to the left occipital cortex and to a posterior sector of the corpus callosum—the splenium) interrupt the flow of visual input into the language network. There is usually a right hemianopia, but the core language network remains unaffected. The patient can understand and produce spoken language, name objects in the left visual hemifield, repeat, and write. However, the patient acts as if illiterate when asked to read even the simplest sentence because the visual information from the written words (presented to the intact left visual hemifield) cannot reach the language network. Objects in the left hemifield may be named accurately because they activate nonvisual associations in the right hemisphere, which in turn can access the language network through transcallosal pathways anterior to the splenium. Patients with this syndrome also may lose the ability to name colors, although they can match colors. This is known as a color anomia. The most common etiology of pure alexia is a vascular lesion in the territory of the posterior cerebral artery or an infiltrating neoplasm in the left occipital cortex that involves the optic radiations as well as the crossing fibers of the splenium. Because the posterior cerebral artery also supplies medial temporal components of the limbic system, a patient with pure alexia also may experience an amnesia, but this is usually transient because the limbic lesion is unilateral.
Apraxia designates a complex motor deficit that cannot be attributed to pyramidal, extrapyramidal, cerebellar, or sensory dysfunction and that does not arise from the patient’s failure to understand the nature of the task. Apraxia of speech is used to designate articulatory abnormalities in the duration, fluidity, and stress of syllables that make up words. Intoning the words may improve articulation. It can arise with CVAs in the posterior part of Broca’s area or in the course of frontotemporal lobar degeneration (FTLD) with tauopathy. Aphemia is a severe form of acute speech apraxia that presents with severely impaired fluency (often mutism). Recovery is the rule and involves an intermediate stage of hoarse whispering. Writing, reading, and comprehension are intact, and so this is not a true aphasic syndrome. CVAs in parts of Broca’s area or subcortical lesions that undercut its connections with other parts of the brain may be present. Occasionally, the lesion site is on the medial aspects of the frontal lobes and may involve the supplementary motor cortex of the left hemisphere. Ideomotor apraxia is diagnosed when commands to perform a specific motor act (“cough,” “blow out a match”) or pantomime the use of a common tool (a comb, hammer, straw, or toothbrush) in the absence of the real object cannot be followed. The patient’s ability to comprehend the command is ascertained by demonstrating multiple movements and establishing that the correct one can be recognized. Some patients with this type of apraxia can imitate the appropriate movement (when it is demonstrated by the examiner) and show no impairment when handed the real object, indicating that the sensorimotor mechanisms necessary for the movement are intact. Some forms of ideomotor apraxia represent a disconnection of the language network from pyramidal motor systems so that commands to execute complex movements are understood but cannot be conveyed to the appropriate motor areas. Buccofacial apraxia involves apraxic deficits in movements of the face and mouth. Limb apraxia encompasses apraxic deficits in movements of the arms and legs. Ideomotor apraxia almost always is caused by lesions in the left hemisphere and is commonly associated with aphasic syndromes, especially Broca’s aphasia and conduction aphasia. Because the handling of real objects is not impaired, ideomotor apraxia by itself causes no major limitation of daily living activities. Patients with lesions of the anterior corpus callosum can display ideomotor apraxia confined to the left side of the body, a sign known as sympathetic dyspraxia. A severe form of sympathetic dyspraxia, known as the alien hand syndrome, is characterized by additional features of motor disinhibition on the left hand. Ideational apraxia refers to a deficit in the sequencing of goal-directed movements in patients who have no difficulty executing the individual components of the sequence. For example, when the patient is asked to pick up a pen and write, the sequence of uncapping the pen, placing the cap at the opposite end, turning the point toward the writing surface, and writing may be disrupted, and the patient may be seen trying to write with the wrong end of the pen or even with the removed cap. These motor sequencing problems usually are seen in the context of confusional states and dementias rather than focal lesions associated with aphasic conditions. Limb-kinetic apraxia involves clumsiness in the use of tools or objects that cannot be attributed to sensory, pyramidal, extrapyramidal, or cerebellar dysfunction. This condition can emerge in the context of focal premotor cortex lesions or corticobasal degeneration.
The combination of acalculia (impairment of simple arithmetic), dysgraphia (impaired writing), finger anomia (an inability to name individual fingers such as the index and thumb), and right-left confusion (an inability to tell whether a hand, foot, or arm of the patient or examiner is on the right or left side of the body) is known as Gerstmann’s syndrome. In making this diagnosis, it is important to establish that the finger and left-right naming deficits are not part of a more generalized anomia and that the patient is not otherwise aphasic. When Gerstmann’s syndrome arises acutely and in isolation, it is commonly associated with damage to the inferior parietal lobule (especially the angular gyrus) in the left hemisphere.
Pragmatics refers to aspects of language that communicate attitude, affect, and the figurative rather than literal aspects of a message (e.g., “green thumb” does not refer to the actual color of the finger). One component of pragmatics, prosody, refers to variations of melodic stress and intonation that influence attitude and the inferential aspect of verbal messages. For example, the two statements “He is clever.” and “He is clever?” contain an identical word choice and syntax but convey vastly different messages because of differences in the intonation with which the statements are uttered. Damage to right hemisphere regions corresponding to Broca’s area impairs the ability to introduce meaning-appropriate prosody into spoken language. The patient produces grammatically correct language with accurate word choice, but the statements are uttered in a monotone that interferes with the ability to convey the intended stress and affect. Patients with this type of aprosodia give the mistaken impression of being depressed or indifferent. Other aspects of pragmatics, especially the ability to infer the figurative aspect of a message, become impaired by damage to the right hemisphere or frontal lobes.
Damage to subcortical components of the language network (e.g., the striatum and thalamus of the left hemisphere) also can lead to aphasia. The resulting syndromes contain combinations of deficits in the various aspects of language but rarely fit the specific patterns described in Table 22-1. In a patient with a CVA, an anomic aphasia accompanied by dysarthria or a fluent aphasia with hemiparesis should raise the suspicion of a subcortical lesion site.
Aphasias caused by major cerebrovascular accidents start suddenly and display maximal deficits at the onset. These are the “classic” aphasias described above. Aphasias caused by neurodegenerative diseases have an insidious onset and relentless progression. The neuropathology can be selective not only for gray matter but also for specific layers and cell types. The clinico-anatomic patterns are therefore different from those described in Table 22-1.
Clinical presentation and diagnosis of primary progressive aphasia (PPA)
Several neurodegenerative syndromes, such as typical Alzheimer-type (amnestic) and frontal-type (behavioral) dementias, can also undermine language as the disease progresses. In these cases, the aphasia is an ancillary component of the overall syndrome. When a neurodegenerative language disorder arises in relative isolation and becomes the primary concern that brings the patient to medical attention, a diagnosis of PPA is made.
The impairments of language in PPA have slightly different patterns from those seen in CVA-caused aphasias. Three major subtypes of PPA can be recognized. The agrammatic variant is characterized by consistently low fluency and impaired grammar but intact word comprehension. It most closely resembles Broca’s aphasia or anterior transcortical aphasia but usually lacks the right hemiparesis or dysarthria and has more profound impairments of grammar. Peak sites of neuronal loss (gray matter atrophy) include the left inferior frontal gyrus where Broca’s area is located. The neuropathology is usually an FTLD with tauopathy but can also be an atypical form of Alzheimer’s disease (AD) pathology. The semantic variant is characterized by preserved fluency and syntax but poor single-word comprehension and profound two-way naming impairments. This kind of aphasia is not seen with CVAs. It differs from Wernicke’s aphasia or posterior transcortical aphasia because speech is usually informative, repetition is intact, and comprehension of conversation is relatively preserved, as long as the meaning is not too dependent on words that the patient fails to understand. Peak atrophy sites are located in the left anterior temporal lobe, indicating that this part of the brain plays a critical role in the comprehension of words, especially words that denote concrete objects. The neuropathology is frequently an FTLD with abnormal precipitates of the 43-kDa transactive response DNA-binding protein TDP-43. The logopenic variant is characterized by preserved syntax and comprehension but frequent and severe word-finding pauses, anomia, circumlocutions, and simplifications during spontaneous speech. Peak atrophy sites are located in the temporoparietal junction and posterior temporal lobe, partially overlapping with traditional location of Wernicke’s area. However, the comprehension impairment of Wernicke’s aphasia is absent, perhaps because the underlying white matter, frequently damaged by cerebrovascular accidents, remains relatively intact in PPA. In contrast to Broca’s aphasia or agrammatic PPA, the interruption of fluency is variable so that speech may appear entirely normal if the patient is allowed to engage in small talk. Logopenic PPA resembles the anomic aphasia of Table 22-1 but usually has longer and more frequent word-finding pauses. Patients may also have poor phrase and word repetition, in which case the aphasia resembles the conduction aphasia in Table 22-1. Of all PPA subtypes, this is the one most commonly associated with the pathology of AD, but FTLD can also be the cause. In addition to these three major subtypes, PPA can also present in the form of pure word deafness or Gerstmann’s syndrome.