The Common Vein Copyright 2010
Aphasia is an acquired disorder of the language due to brain damage. Generally speaking, this disorder can be selective, by terms of disorders of reading (alexia) or writing (agraphia). 20% of stroke patients develop aphasia (which is its most common cause)
It is mostly caused by brain injury or degeneration; the left cerebral hemisphere is usually more involved than the right, as language is a function lateralized to the left in the majority of the population, even if the person is left-handed (in about 60% of them). The usual culprits of the injury are stroke, tumors, degenerative disorders and trauma.
Because there are different areas in the brain responsible for different aspects involved in the language mechanism, an injury to any of them could potentially cause in aphasia. This can be a defect in expression of the language, for which the frontal lobe is responsible; a defect in comprehension (parietal lobe); and in the auditory input (superior temporal lobe). Also, the tracts which connect these areas can be injured, resulting in aphasia as well. Depending on the site of dysfunction, a different type of aphasia will result.
Patients present with abruptly onset of symptoms in most cases, due its the etiology. Results in very distinct syndromatic presentations depending of the area affected and primarily causing the aphasia. Broca, Wernicke, conduction, and global aphasias are the classical ones, but do not account for all of them. These are part of a wider group called cortical aphasias.
In Broca’s aphasia, there is a deficit in the ability to produce speech; the articulation may be impaired, but comprehension is relatively spared. Phrases tend to be short, because there is an increased effort by the patient to produce words.
In Wernicke’s aphasia, the language is actually fluently expressed, but it does not carry any meaning, missing nouns, verbs and carrying non-existing words.
In conduction aphasia, speech is fluent, but with phonemic error. There is awareness of the deficit and pause are frequent to correct them
In global aphasia there is a deficit in all aspects of language: speech, repetition, comprehension, naming, reading, and writing.
Diagnosis is made through physical examination and mostly detailed mental state examination, which will provide enough information to categorize the findings into one of the aphasia syndromes. Because stroke is the most common cause, neuroimaging is required to localize and diagnose the cause of aphasia, through CT and MRI. Contrast could be required for tumors. If dementia is a concern, and gross atrophy is not seen in traditional neuroimaging, nuclear scans can be done, for detection of reduced blood flow / metabolic activity in certain foci.
Treatment depends on the etiology in its acute onset. For the chronic presentations, speech and language therapy are the mainstay of care.