Aphasia is an acquired disorder of language due to brain damage. It may occur secondary to brain injury or degeneration and involves the left cerebral hemisphere to a greater extent than the right.
Signs and symptoms
Aphasia develops abruptly in patients with a stroke or head injury. Patients with neurodegenerative diseases or mass lesions may develop aphasia insidiously.
People with aphasia may exhibit the following symptoms:
Difficulty using words and sentences (expressive aphasia)
Difficulty understanding others (receptive aphasia)
Difficulty with both using words and understanding (global aphasia)
Patients may also experience problems with spoken and written language. Typically, reading and writing are more impaired than talking or understanding.
See Clinical Presentation for more detail.
Careful assessment of language function with an evaluation of neighborhood signs is important in the diagnosis of the localization and cause of aphasia. These signs include:
difficulties with vision, especially hemianopia
deficits of motor or sensory function
neurobehavioral deficits such as alexia, agraphia, acalculia, or apraxia
Components of bedside language examination include assessments of spontaneous speech, naming, repetition, comprehension, reading, and writing. Although bedside examination can usually reveal the type of aphasia, formal cognitive testing by a neuropsychologist or speech/language therapist may be important to determine fine levels of dysfunction, to plan therapy, and to assess the patient's potential for recovery.
Because aphasia is most often caused by stroke, neuroimaging is required to localize and diagnose the cause of aphasia. CT scanning and MRI are the mainstays of neuroimaging.
See Workup for more detail.
The treatment of a patient with aphasia depends on the cause of the aphasia syndrome. Acute stroke treatment for the aphasic patient, such as intravenous tPA, intra-arterial interventional treatments, carotid endarterectomy and stenting, or even blood pressure manipulation may help to alleviate the deficit. Surgery for a subdural hematoma or brain tumor may be beneficial. In infections such as herpes simplex encephalitis, antiviral therapy may help the patient recover.
If brain damage is mild, a person may recover language skills without treatment. However, most people undergo speech and language therapy to rehabilitate their language skills and supplement their communication experiences. Speech and language therapy is the mainstay of care for patients with aphasia.
Aphasia is an acquired disorder of language due to brain damage. Aphasia does not include (1) developmental disorders of language, often called dysphasia in the United States; (2) purely motor speech disorders, limited to articulation of speech via the oral-motor apparatus, referred to as stuttering, dysarthria, and apraxia of speech; or (3) disorders of language that are secondary to primary thought disorders, such as schizophrenia.
Encompassed under the term aphasia are selective, acquired disorders of reading (alexia) or writing (agraphia). Closely related to aphasia are the family of disorders called apraxias (disorders of learned or skilled movements), agnosias (disorders of recognition), acalculias (disorders of calculation ability), and more global neurobehavioral deficits such as dementia and delirium. Such related syndromes may coexist with aphasia or exist independently.
Aphasia may occur secondary to brain injury or degeneration and involves the left cerebral hemisphere to a greater extent than the right. Language function lateralizes to the left hemisphere in 96-99% of right-handed people and 60% of left-handed people. Of the remaining left-handed people, about one half have mixed hemisphere language dominance, and about one half have right hemisphere dominance. Left-handed individuals may develop aphasia after a lesion of either hemisphere, but the syndromes from left hemisphere injury may be milder or more selective than those seen in right-handed people.
Most aphasias and related disorders are due to stroke, head injury, cerebral tumors, or degenerative diseases. The neuroanatomic substrate of language comprehension and production is complex, including auditory input and language decoding in the superior temporal lobe, analysis in the parietal lobe, and expression in the frontal lobe, descending via the corticobulbar tracts to the internal capsule and brainstem, with modulatory effects of the basal ganglia and the cerebellum.
Aphasia syndromes have been described based on patterns of abnormal language expression, repetition, and comprehension. These classical syndromes have been roughly correlated with specific left hemisphere locations, though clear overlaps and individual differences make the aphasia syndromes limited in specificity. Patients may lose the ability to produce speech, to comprehend speech, to repeat, and to hear and read words in many nuanced ways. Classical aphasia syndromes (see Aphasia syndromes in History) include global, Broca, Wernicke, and conduction aphasia, as well as transcortical motor, transcortical sensory, and transcortical mixed aphasia. Pure alexia and optic aphasia are often discussed with the classical aphasias.
Language function can be parsed in several important ways other than assignment to the classical aphasia syndromes. A variety of types of evidence have noted that certain specific language functions (such as naming pictures) activate widespread neural networks involving many parts of both hemispheres of the brain. Producing, receiving, and interpreting speech requires specific and distinct cognitive processes such as phonologic decoding and encoding, orthographic decoding and encoding (for reading), lexical access, lexical-semantic representations of words, and semantic interpretation of language. Differentiation of these processes involves testing patients with different aphasia types and attempting to find double dissociations among groups of patients to determine the neurologic basis of specific cognitive processes.
The lesion method, the principal source of information about aphasia from autopsy studies in the 19th and early to mid 20th centuries and from brain imaging modalities since the 1970s, remains a useful source of information. However, it has been abetted by cortical stimulation studies, mainly in patients with epilepsy, and functional neuroimaging, such as fMRI and PET scanning often carried out during language testing in healthy individuals, to determine the language function of specific areas of the brain.
Data on incidence of aphasia in the United States are limited. Aphasia occurs in a variety of cerebrovascular, traumatic, and degenerative conditions. Stroke is likely the most common cause of aphasia, and it has been estimated that about 20% of stroke patients develop aphasia. More than 700,000 strokes occur in the United States each year, and approximately 170,000 new cases of aphasia every year are related to stroke. The number of patients with language disorders secondary to traumatic brain injury, brain tumors, and other brain lesions such as arteriovenous malformations is not precisely known. Patients with neurodegenerative disorders such as Alzheimer disease and frontotemporal dementia frequently manifest language deficits. The prevalence of Alzheimer disease in the United States is approximately 5 million cases.
Aphasia is a condition, not a disease; therefore, it has no attributable mortality rate.
No reliable data exist on the incidence of aphasia in different racial groups. Within disease entities, however, such differences are well known. In stroke, for example, African Americans have almost a 2-fold higher incidence as compared with whites. In addition, specific types of stroke, such as cerebral hemorrhage, lacunar infarctions, and intracranial artery stenoses, are known to be more common in African Americans than Caucasians. One might therefore surmise that poststroke aphasias would be more common in African Americans.
Not enough data are available to evaluate differences in the incidence and clinical features of aphasia in men and women. Some studies suggest a lower incidence of aphasia in women because they may have more bilaterality of language function. Differences may also exist in aphasia type, with more women than men developing Wernicke aphasia.
Age may be an important factor in recovery. Some studies suggest that recovery from aphasia due to a stroke is less favorable in patients older than age 70 than in younger patients. However, at any age, recovery of various degrees can occur, even at times remote from the brain injury.
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