Monday, January 25, 2010
31 - Aphasia
The major language centers of the brain. The motor and sensory areas are presented as landmarks. Interconnecting functional pathways are indicated by letters: A) The connection between Wernicke's and Broca's areas, mediating expression of language utterances in speech; B) The connection between Broca's area and the primary motor area; C) Connection between primary auditory perception and Wernicke's area; D) Connection between vision and Wernicke's area, mediating reading ability; E) Connection between somatosensory perception (tactile, pain, cold/hot, position sense) and Wernicke's area, this would mediate language comprehension by tracing letters on the skin or reading braille.
Aphasia: Loss or impairment of language comprehension or production is called aphasia. The difficulties in language function must not be attributable to impairment of the speech or writing production apparatus, such as muscles of the tongue and throat, or peripheral sensory loss. Although the person suffering such impairment may have trouble articulating a language utterance, the brain centers moderating language are presumably intact.
The study of aphasia began with Broca's original case reports of 1861. The first patient could only utter the phrase "tan". Post mortem examination of his brain revealed a fluid filled cavity involving the left frontal lobe. Broca examined another case in which the patient could comprehend but not express language in speech or writing. The patient also had a prominent lesion of the left frontal lobe. In 1865, Broca reported on eight patients who had lost speech and all had left hemisphere lesions.
Broca's reports generated great interest in aphasia and numerous cases were reported that included impairment of the comprehension of language as well as expression. In 1874, Wernicke summarized all these aphasia manifestations and proposed a scheme that included a type of sensory (Wernicke's) aphasia, in which the patient cannot comprehend language and speaks in a fluent, garbled style. This aphasia was caused by lesion of an auditory association area in the superior temporal lobe (Wernicke's area). He also proposed an aphasia syndrome involving the disconnection of the language production centers in the frontal lobe from the comprehension centers in the temporal lobe. This "conduction" aphasia would include an extreme difficulty in repeating language utterances.
The further study of aphasia has essentially followed Wernicke's basic model of analysis. However, numerous subtypes of aphasia have been proposed. Elaborate theories of language function and its mediation by the brain have developed and component language process, such as spelling, writing and reading have been analyzed in detail. Finally, modern neuropsychology includes the study of language mediated by the right hemisphere.
Broca's Aphasia :
Patient's with this form of language disorder cannot fluently express language utterances. Their speech is extremely impoverished or they may be functionally mute. It is not uncommon for their speech to be reduced to a stereotypic nonsense phrase, such as "tan", or "Ichaboty ama". These phrases may be uttered fluently in response to any question, as if they were the remaining language pattern that Broca's area could formulate. Often, phrases such as "yes" and "no", curse words and non language emotional expressions remain intact. Frustrations with language expression often result in curses, or emotionally laden sounds that express frustration. They may also represent the language contribution of the right hemisphere.
Writing is also affected. Although the patients with Broca's aphasia typically have right-sided hemiplegia, their writing disorder extends beyond simple motor incoordination or weakness. Their language production through writing is similar to language production through speech.
In contrast, comprehension of language is relatively intact. The patient understands oral communications from others, and reading may be normal. Although comprehension is invariably superior to expressions, the patient with Broca's aphasia may still have some impairment of comprehension. This distinction involves the contrast between comprehension and expression rather than a complete absence of comprehension deficit.
Patients with Broca's aphasia also have associated findings that aid in clinical diagnosis. First, since the left frontal lobe is involved, they will usually have right-sided hemiplegia. Since most people are left-hemisphere dominant for motor function, damage to motor central areas of the left hemisphere results in extreme motor impairment that compromises the accurate examination of writing abilities. Second, the sensory areas in the posterior parts of the brain are usually intact and it is therefore uncommon for patients with Broca's aphasia to have any sensory deficits. Third, patients with Broca's aphasia often have an apraxia of the left, intact side, that further compromises motor function.
Wernicke's Aphasia :
This aphasia is associated with fluent language output that is severely disorganized, sometimes to the point of an incomprehensible babble. The language constructions are replete with semantic substitutions and paraphasic jargon. Even when the language utterance is grammatically correct, it may be nonsense because of semantic substitution. (e.g., How many sorters were on the wall?).
The other major characteristic is the severe disturbance of comprehension. The patient with Wernicke's aphasia has great difficulty understanding language utterances spoken by others or presented in visual form. This includes their own garbled speech, such that many patients do not understand that their speech is disturbed. Because of this difficulty patients with Wernicke's aphasia have great difficulty repeating phrases presented to them.
They also have trouble in naming objects presented to them. Writing productions have the same quality as speech. Writing samples include nonsense words and semantic substitutions. Reading is severely compromised. The patient often confabulates a reading of text that is garbled nonsense.
Some versions of Wernicke's aphasia include worse visual (reading) than auditory (oral) comprehension. Such patients can understand what others say to them better than comprehending material presented in written form. The opposite pattern is also possible and patients may read better than comprehend oral language. If reading is intact and auditory comprehension is severely impaired then the syndrome is called "pure word deafness". The opposite pattern in which auditory comprehension is intact but reading is impaired is called "pure word blindness".
Wernicke's aphasia results from lesions of the left hemisphere in the region of the auditory association cortex of the superior temporal lobe (Wernicke's area). This area is colored red in the figure above.
Conduction Aphasia :
The comprehension functions of Wernicke's area must interact with the motor and expressive components of Broca's area in order for anyone to engage in meaningful communication. Wernicke proposed the term "conduction aphasia" to describe the language impairment associated with disconnection of these two major language centers. This would involve disconnection of pathway "A" in the figure above.
Patient's with conduction aphasia have fluent paraphasic expression that is characterized by numerous phonetic substitutions (e.g. "fetter" for "better"). Their comprehension is intact. They have a severe impairment of repetition. Reading aloud is characterized by paraphasic output but comprehension is good. Writing impairment is mild.
Lesion of the white matter pathways that connects these areas results in conduction aphasia. The arcuate fasciculus is one the major pathways involved.
Global Aphasia :
This refers to the virtual complete loss of language function as a result of lesion to both Broca's and Wernicke's areas. Surrounding areas of the left hemisphere are usually injured as well. The patient has severe deficits of expression, comprehension, reading, writing, naming, and ability to repeat. Since the left hemisphere is extensively injured, it is possible that the patients remaining language skills represent the language abilities of the right hemisphere.
Transcortical Aphasia - Mixed :
A rare aphasic disorder involves the isolation of both Broca's and Wernicke's areas. The patient has a virtual compulsion to repeat utterances to the point of appearing echolalic. Other language abilities, such as comprehension, naming, expression, and reading are impaired. The patient may not utter any language unless spoken to. Lesion of the "watershed" areas perfused by the middle cerebral artery result in this isolation of the language areas.
Transcortical Aphasia - Motor :
This is a subtype of transcortical aphasia in which motor impairment is greater in comparison to sensory and comprehension impairment. Speech is nonfluent except for repetition. Comprehension is preserved. Reading is consequently intact but writing is impaired. This disorder is similar to Broca's aphasia except for the good ability to repeat. Lesions surrounding Broca's area produce this syndrome.
Transcortical Aphasia - Sensory :
Patients with this subtype of transcortical aphasia have intact repetition and a greater difficulty with comprehension than speech production. Speech is fluent with occasional paraphasic intrusions. The patient appears to have a compulsion to repeat and echo the speech of others. Comprehension is severely limited, resulting in poor reading and writing content. Lesions of sensory association areas surrounding Wernicke's area result in this disorder.
Patients who recover from any form of aphasia often have naming difficulties as a residual symptom. Patients with anomia have a characteristic conversational speech that includes normal fluent output with occasional interruptions as the patient pauses to find the next correct word. These words are invariably names that are not easily retrieved. The patient may also talk around the forgotten word. This feature is called circumlocution. Anomia does not have clear localizing significance. Many lesions of the left hemisphere will produce anomia. Indeed, mild anomia is characteristic of normal language ability. The anomia associated with aphasia appears as a severe form of the word-finding problems that are suffered by everyone.
*Most common language disturbance seen in Head trauma is Anomic Aphasia.
*Most common language disturbance seen in Metabolic encephalopathy is Anomic Aphasia.
*Most common language disturbance seen in Alzheimer's disease is Anomic aphasia.
This disorder is also called anarthria, subcortical motor aphasia and pure-word dumbness. Patients with this disorder become acutely mute. They recover to have a soft, slow grammatically intact speech. Comprehension, reading and writing are normal. In contrast to pure mutism, they show frustration when unable to speak. Acute lesion of supplementary motor or Broca's areas of the frontal lobe produce this syndrome.
Pure Word Deafness :
This refers to a specific deficit of perception of spoken language. Other auditory perception is intact. Speech is intact but some garbled language may be present at the onset of illness. Writing is normal. Reading may be impaired. Lesion of the primary auditory cortex contiguous to Wernicke's area produces this syndrome.
Alexia without Agraphia (pure alexia)
This disorder involves a disconnection of the language centers from visual perceptual areas. The patient cannot read but other language functions are intact. The patient must have a lesion of the left occipital lobe that also includes the pathways connecting the visual perceptual areas. These pathways make up the splenium of the corpus callosum. This produces a visual field cut on the right side and visual information can only be perceived by the right hemisphere. Since the connections between the right hemisphere visual perception areas and the left hemisphere language centers are lesioned, the patient cannot decode the language related visual information and cannot read. However, the patient comprehends auditory information and can write and speak normally. This results in the paradoxical symptom of a patient who can write spontaneously but cannot read his/her own writing.
Agraphic alexia (Parietal alexia)
This refers to a severe disorder of both reading and writing but auditory comprehension and speech are intact. Acalculia, right-left spatial disorientation and naming deficits are common associated symptoms. Lesions of the left angular gyrus of the parietal lobe result in this syndrome.
This disorder is characterized by agraphia without other language disturbance. Patients make well-formed letters but have characteristic spelling errors. Lesion of the second frontal convolution (Exner's area), superior parietal lobule and perisylvian areas produce this syndrome.
SUMMARY TABLE :
Nonfluent Speech, Poor Repetition, Good Comprehension, Poor Naming, Right-side Hemiplegia, Few Sensory Deficits
Fluent Speech, Poor Repetition, Poor Comprehension, Poor Naming, No Right-side Hemiplegia, Some Sensory Deficits
Fluent Speech, Poor Repetition, Good Comprehension, Poor Naming, No Right-side Hemiplegia, Some Sensory Deficits
Nonfluent Speech, Poor Repetition, Poor Comprehension, Poor Naming, Right-side Hemiplegia, Sensory Deficits
Nonfluent Speech, Good Repetition, Good Comprehension, Poor Naming, Some Right-side Hemiplegia, No Sensory Deficits
Fluent Speech, Good Repetition, Poor Comprehension, Poor Naming, Some Right-side Hemiplegia, Sensory Deficits
Nonfluent Speech, Good Repetition, Poor Comprehension, Poor Naming, Some Right-side Hemiplegia, Sensory Deficits
Fluent Speech, Good Repetition, Good Comprehension, Poor Naming, No Right-side Hemiplegia, No Sensory Deficit.
Language function is examined using assessment tools designed for two levels of ability: 1) Basic language function, such as simple naming, spelling, repetition and comprehension; 2) Complex language function, such as vocabulary and semantic reasoning. The important constructs to assess in language are spontaneous speech or fluency, naming, repetition, and comprehension. By delineating a profile of performance in each of these areas the clinician can begin to understand the location of the patient's injury and the nature of the language impairment. The following are a selection of language constructs and some assessment strategies:
This is assessed by requesting the patient to engage in conversation, make social greetings, and describe something, such as a picture. Observations should be made of the patient's speech production. Patients with anterior lesions will have halting, agrammatic, dysprosodic speech which features substantive words, such as the major nouns and verbs. Patients with posterior lesions may speak fluently, with well articulated and prosodic speech, but the speech content will be empty. Paraphasias of semantic or phonemic origin are common.
Repetition is assessed by having the patient repeat simple words, and then progressing to more complicated phrases and sentences.
Comprehension is assessed by asking the patient questions which determine accuracy of understanding. This must be distinguished from speech output since many aphasic patients can understand but they cannot indicate their understanding by speaking. Assessment of comprehension includes simple yes/no questions ("do you sit on a chair", "Is your name Joe"), following one step commands ("pick up the keys") and following more complicated two- and three-step commands.
Naming is assessed by asking the patient to name common objects or pictures of objects. It is important to distinguish between naming impairment, visual/perceptual disturbance, and educational or cultural limitations. Patients should be provided with a descriptive cue ("its something you eat") if they fail to immediately name the object. Also, one cannot assume the patient has a naming deficit if they never knew the name of the object. This can usually be determined by providing a phonemic cue ("the word starts with sphy, for sphynx"). Patients with true naming deficits will usually produce the target word when provided with a phonemic cue, whereas patients who are not familiar with the word will show no response to phonemic cueing.