Aphasia classification
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
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Classification Schemes
Classifying the different subtypes of aphasia is difficult and has led to disagreements among experts. The locationist model is the original model, but modern anatomical techniques and analyses have shown that precise connections between brain regions and symptom classification don't exist. The neural organization of language is complicated; language is a comprehensive and complex behavior and it makes sense that it isn't the product of some small, circumscribed region of the brain.
No classification of patients in subtypes and groups of subtypes is adequate. Only about 60% of patients will fit in a classification scheme such as fluent/nonfluent/pure aphasias. There is a huge variation among patients with the same diagnosis, and aphasias can be highly selective. For instance, patients with naming deficits (anomic aphasia) might show an inability only for naming buildings, or people, or colors. [1]
The Locationist Model
The locationist model attempts to classify the aphasia by major characteristics and then link these to areas of the brain in which the damage has been caused. The initial two categories here were devised by early neurologists working in the field, namely Paul Broca and Carl Wernicke. Other researchers have added to the model, resulting in it often being referred to as the "Boston-Neoclassical Model". The most prominent writers on this topic have been Howard Goodglass and Edith Kaplan.
- Individuals with Broca's aphasia (also termed expressive aphasia) were once thought to have ventral temporal damage though more recent work by Nina Dronkers using imaging and 'lesion analysis' has revealed that patients with Broca's Aphasia have lesions to the medial insular cortex. Broca missed these lesions because his studies did not disect the brains of diseased patients so only the more temporal damage was visible. Individuals with Broca's aphasia often have right-sided weakness or paralysis of the arm and leg because the frontal lobe is also important for body movement.
- In contrast to Broca's aphasia, damage to the temporal lobe may result in a fluent aphasia that is called Wernicke's aphasia (also termed sensory aphasia). These individuals usually have no body weakness because their brain injury is not near the parts of the brain that control movement.
- Working from Wernicke's model of aphasia, Ludwig Lichtheim proposed five other types of aphasia but these were not tested against real patients until modern imaging made more indepth studies available. The other five types of aphasia in the locationist model are:
- Pure word deafness
- Conduction aphasia
- Apraxia of speech, which is now considered a separate disorder in itself.
- Transcortical motor aphasia
- Transcortical sensory aphasia
- Anomia is another type of aphasia proposed under what is commonly known as the Boston-Neoclassical model, which is essentially a difficulty with naming. A final type of aphasia, global aphasia, results from damage to extensive portions of the language areas of the brain.
Fluent, non-fluent and "pure" aphasias
The different types of aphasia can be divided into three categories: fluent, non-fluent and "pure" aphasias.[2]
- Fluent aphasias, also called receptive aphasias, are impairments related mostly to the input or reception of language, with difficulties either in auditory verbal comprehension or in the repetition of words, phrases, or sentences spoken by others. Speech is easy and fluent, but there are difficulties related to the output of language as well, such as paraphasia. Examples of fluent aphasias are: Wernicke's aphasia, Transcortical sensory aphasia, Conduction aphasia, Anomic aphasia
- Nonfluent aphasias, also called expressive aphasias are difficulties in articulating, but in most cases there is relatively good auditory verbal comprehension. Examples of nonfluent aphasias are: Broca's aphasia, Transcortical motor aphasia, Global aphasia
- "Pure" aphasias are selective impairments in reading, writing, or the recognition of words. These disorders may be quite selective. For example, a person is able to read but not write, or is able to write but not read. Examples of pure aphasias are: Alexia, Agraphia, Pure word deafness
The Cognitive Neuropsychological Model
The cognitive neuropsychological model builds on cognitive neuropsychology. It assumes that language processing can be broken down into a number of modules, each of which has a specific function. Hence there is a module which recognises phonemes as they are spoken and a module which stores formulated phonemes before they are spoken. Use of this model clinically involves conducting a battery of assessments (usually from the PALPA), each of which tests one or a number of these modules. Once a diagnosis is reached as to where the impairment lies, therapy can proceed to treat the individual module.
The following table summarizes some major characteristics of different types of aphasia:
| Type of aphasia | Repetition | Naming | Auditory comprehension | Fluency | Presentation |
|---|---|---|---|---|---|
| Wernicke's aphasia | mild–mod | mild–severe | defective | fluent paraphasic | Individuals with Wernicke's aphasia may speak in long sentences that have no meaning, add unnecessary words, and even create new "words" (neologisms). For example, someone with Wernicke's aphasia may say, "You know that smoodle pinkered and that I want to get him round and take care of him like you want before", meaning "The dog needs to go out so I will take him for a walk". They have poor auditory and reading comprehension, and fluent, but nonsensiscal, oral and written expression. Individuals with Wernicke's aphasia usually have great difficulty understanding the speech of both themselves and others and are therefore often unaware of their mistakes. They are also often unaware of their surroundings, and may present a risk to themselves and others around them. |
| Transcortical sensory aphasia | good | mod–severe | poor | fluent | Similar deficits as in Wernicke's apahsia, but repetition ability remains intact. |
| Conduction aphasia | poor | poor | relatively good | fluent | Caused by damage to the arcuate fasciculus, the structure that transmits information between Wernicke's area and Broca's area. Auditory comprehension is near normal, and oral expression is fluent with occasional paraphasic errors. Repetition ability is poor. |
| Anomic aphasia | mild | mod–severe | mild | fluent | Anomic aphasia, is essentially a difficulty with naming. The patient may have difficulties naming certain words, linked by their grammatical type (e.g. difficulty naming verbs and not nouns) or by their semantic category (e.g. difficulty naming words relating to photography but nothing else) or a more general naming difficulty. Patients tend to produce grammatic, yet empty, speech. Auditory comprehension tends to be preserved. |
| Broca's aphasia | mod–severe | mod–severe | mild difficulty | non-fluent, effortful, slow | Individuals with Broca's aphasia frequently speak short, meaningful phrases that are produced with great effort. Broca's aphasia is thus characterized as a nonfluent aphasia. Affected people often omit small words such as "is", "and", and "the". For example, a person with Broca's aphasia may say, "Walk dog" meaning, "I will take the dog for a walk". The same sentence could also mean "You take the dog for a walk", or "The dog walked out of the yard", depending on the circumstances. Individuals with Broca's aphasia are able to understand the speech of others to varying degrees. Because of this, they are often aware of their difficulties and can become easily frustrated by their speaking problems. It is associated with right hemiparesis, meaning that there will be paralysis of the patient's right arm, leg, and face. |
| Transcortical motor aphasia | good | mild–severe | mild | non-fluent | Similar deficits as Broca's aphasia, except repetition ability remains intact. Auditory comprehension is generally fine for simple conversations, but declines rapidly for more complex conversations. It is associated with right hemiparesis, meaning that there will be paralysis of the patient's right arm, leg, and face. |
| Global aphasia | poor | poor | poor | non-fluent | Individuals with global aphasia have severe communication difficulties and will be extremely limited in their ability to speak or comprehend language. They may be totally nonverbal, and/or only use facial expressions and gestures to communicate. It is associated with right hemiparesis, meaning that there will be paralysis of the patient's right arm, leg, and face. |
| Transcortical mixed aphasia | moderate | poor | poor | non-fluent | Similar deficits as in global apahsia, but repetition ability remains intact. |
| Subcortical aphasias | Characteristics and symptoms depend upon the site and size of subcortical lesion. Possible sites of lesions include the thalamus, internal capsule, and basal ganglia. Subtypes include subcortical motor aphasia and subcortical sensory aphasia |
Other less common subtypes include:
A combination of subtypes is possible.
Primary and Secondary Aphasia
Aphasia can be divided into primary and secondary aphasia.[3]
Primary Aphasia
This form of aphasia is due to problems with language-processing mechanisms.
Secondary Aphasia
This form of aphasia is the result of other problems, like memory impairments, attention disorders, or perceptual problems.
References
- ↑ Kolb & Whishaw: Fundamentals of Human Neuropsychology (2003), page 502, 505, 511.
- ↑ Kolb & Whishaw: Fundamentals of Human Neuropsychology (2003), pages 502-504. The whole paragraph "fluent, non-fluent and pure aphasias" is written with help of this reference.
- ↑ http://christofflab.psych.ubc.ca/psych260/docs/L12-Language.pdf