Definition
Aphasia is a communication disorder that occurs after language has been developed, usually in adulthood. Not simply a speech disorder, aphasia can affect the ability to comprehend the speech of others, as well as the ability to read and write. In most instances, intelligence per se is not affected.
Description
Aphasia has been known since the time of the ancient Greeks. However, it has been the focus of scientific study only since the mid-nineteenth century. Although aphasia can be caused by a head injury and neurologic conditions, its most common cause is stroke, a disruption of blood flow to the brain, which affects brain metabolism in localized areas of the brain. The onset of aphasia is usually abrupt, and occurs in individuals who have had no previous speech or language problems. Aphasia is at its most severe immediately after the event that causes it. Although its severity commonly diminishes over time through both natural, spontaneous recovery from brain damage and from clinical intervention, individuals who remain aphasic for two or three months after its onset are likely to have some residual aphasia for the rest of their lives. However, positive changes often continue to occur, largely with clinical intervention, for many years. The severity of aphasia is related to a number of factors, including the severity of the condition that brought it about, general overall health, age at onset, and numerous personal characteristics that relate to motivation.
Demographics
The National Aphasia Association estimates that approximately 25–40% of stroke survivors develop aphasia. There are approximately one million persons in the United States with aphasia, and roughly 100,000 new cases occur each year. There are more people with aphasia than with Parkinson's disease, cerebral palsy, or muscular dystrophy.
Causes and symptoms
Although aphasia occasionally results from damage to subcortical structures such as basal ganglia or the thalamus that has rich interconnections to the cerebral cortex, aphasia is most frequently caused by damage to the cerebral cortex of the brain's left hemisphere. This hemisphere plays a significant role in the processing of language skills. However, in about half of left-handed individuals (and a few right-handed persons), this pattern of dominance for language is reversed, making right-hemisphere damage the cause of aphasia in this small minority. Because the left side of the brain controls movement on the right side of the body (and vice versa), paralysis affecting the side of the body opposite the side of brain damage is a frequent co-existing problem. This condition is called hemiplegia and can affect walking, using one's arm, or both. If the arm used for writing is paralyzed, it poses an additional burden on the diminished writing abilities of some aphasic individuals. If paralysis affects the many muscles involved in speaking, such as the muscles of the tongue, this condition is called dysarthria. Dysarthria often co-occurs with aphasia.
There are a few more problems that can result from the same brain injury that produces aphasia, and complicate its presentation. Most notable among them are the problems collectively called apraxia, which influences one's ability to program movement. Apraxic difficulties make voluntary movements difficult and hard to initiate. Apraxia of speech results in difficulty initiating speech and in making speech sounds consistently. It frequently co-occurs with both dysarthria and aphasia. Finally, sensory problems such as visual field deficits (specifically, hemianopsia) and changes in (or absence of) sensation in arms, legs, and tongue commonly occur with aphasia.
There are neurological disorders other than aphasia that also manifest difficulty with language. This makes it important to note what aphasia is not. Traumatic brain injury and dementias such as Alzheimer's disease are excellent examples. Although brain injury is a cause of aphasia, most head injuries produce widespread brain damage and result in other neuropsychological and cognitive disorders. These disorders often create language that is disturbed in output and form, but are typically the linguistic consequences of cognitive disturbances. In Alzheimer's disease, the situation is much the same. Language spoken by individuals with Alzheimer's reflect their cognitive problems, and, as such, differ from the language retrieval problems typically designated as aphasia. In short, if the damage that results in language problems is general and produces additional intellectual problems, then aphasia is a correct diagnosis. In the absence of other significant intellectual problems, then the language disorder is probably localized to the brain's language processing areas and is properly termed aphasia.
Finally, aphasia is not conventionally used to refer to the developmental language learning problems encountered by some atypically developing children. However, when children who have been previously developing language normally have a stroke or some other type of localized brain damage, then the aphasia diagnosis is appropriate.
Aphasia manifests different language symptoms and syndromes as a result of where in the language-dominant hemisphere the damage has occurred. The advent of neuroimaging has improved the ability to localize the area of brain damage. Nevertheless, the different general patterns of language strengths and weaknesses, as well as unexpected dissociations in language function, can explain how normal language is processed in the brain, as well as provide insights into intervention for aphasia.
Aphasic individuals almost uniformly have some difficulty in using the substantive words of their native language. Most experts in aphasia recognize that aphasia varies along two major dimensions: auditory comprehension ability and fluency of speech output. In reality, aphasic behaviors vary greatly from individual to individual, and fluctuate in a given individual as a result of fatigue and other factors. In addition, largely in relationship to lesion size, aphasias differ in overall severity.
Nonfluent aphasia
Frontal cortex is responsible for shaping, initiating, and producing behaviors. Individuals with nonfluent aphasia characteristically have brain damage affecting Broca's area of the cortex and the frontal brain areas surrounding it. These areas are responsible for formulating sound, word, and sentence patterns. Damage to the anterior speech areas results in slow, labored speech with limited output and prosody and difficulty in producing grammatical sentences. Because the motor cortex is closely adjacent, nonfluent Broca's aphasia, by far the most common nonfluent variant, is quite likely to co-occur with motor problems.
Several additional characteristics of nonfluent aphasia can be noted: in nonfluent aphasia verbs and prepositions are disproportionately affected; speech errors occur mostly at the level of speech sounds, producing sound transpositions and inconsistencies; auditory comprehension is only minimally affected; reading abilities parallel comprehension, writing problems parallel speech output, but are sometimes further complicated by hemiplegia; finally, there is an inability to repeat what someone else says.
Fluent aphasia
Fluent aphasias occur when damage occurs in the posterior language areas of the brain, where sensory stimuli from hearing, sight, and bodily sensation converge. In fluent aphasia, the prosody and flow of speech is maintained; one typically must listen closely to recognize that the speech is not normal. Because this posterior damage is located far from the motor areas in the frontal lobes, individuals with fluent aphasia seldom have co-existing difficulty with the mechanics of speech, arm use, or walking. There are three major variants of fluent aphasia, each thought to occur as a function of disruption to different posterior brain regions.
WERNICKE'S APHASIA Wernicke's aphasia results from temporal lobe damage, where auditory input to the brain is received. The essential characteristic is that individuals with this disorder have disproportionate difficulty in understanding spoken and written language. They also have problems comprehending and monitoring their own speech. They are often verbose, and frequently use inappropriate and even jargon words when they speak. Reading and writing are impaired in similar ways to auditory comprehension and speech output. Their comprehension difficulties preclude their being able to repeat others' words.
ANOMIC APHASIA Most people, particularly as they grow older, have trouble with the names of persons and things; all aphasic persons experience these difficulties. But when brain damage occurs in the area of the posterior brain where information from temporal, parietal, and occipital lobes converge, this problem of naming is much more pervasive than for normal and aphasic speakers alike. Most anomic aphasic individuals have excellent auditory comprehension and read well. But for most of them, writing mirrors speech, and individuals with anomic aphasia can take advantage of words provided by others. Hence, their repetition ability is good. Although anomic aphasia is classified as a fluent syndrome, frequent stops, starts, and word searches typically make speech choppy in between runs of fluency.
CONDUCTION APHASIA Individuals with conduction aphasia are thought to have a discrete brain lesion that disrupts the pathways that underlie the cortex and connect the anterior and posterior speech regions. These individuals have good comprehension, as well as high awareness of the errors that they make. Placement of their brain damage also suggests that there should be little interference with speech production, reading, and writing. However, damage to the neural links between posterior and anterior speech areas makes it quite difficult for these individuals to correct the errors they hear themselves making. Conduction aphasia also affects the ability to repeat the speech of others or to take advantage of the cues others provide. The speech of individuals with this problem includes many inappropriate words, typically involving inappropriate sequences of sounds.
UNUSUAL APHASIA SYNDROMES There are a few other rare aphasic syndromes (called "transcortical aphasias") and unique dissociations in aphasic patterns. The above aphasias represent the most common distinctive syndromes. However, they are estimated to account for only approximately 40% of individuals with aphasia.
MIXED AND GLOBAL APHASIA The remaining majority, about 60% of aphasic individuals, have aphasias that result from brain lesions involving both the anterior and posterior speech areas. Their aphasias, thus, affect both speech production and comprehension. They frequently have reading and writing disorders as well. Individuals with mixed and global aphasia are also very likely to have hemiplegia and dysarthria, as well as a variety of sensation losses. Depending upon the severity of these symptoms, people with mild-to-moderate symptomatology of this type are said to have mixed aphasia; global aphasia describes individuals with extensive difficulties in all language skills.
Diagnosis
As an aid to accurate diagosis immediately following stroke, it is important to differentiate aphasia from cognitive disorders such as confusion and disorientation. To this end, brief, but general testing of the language functions (naming, comprehension, reading, writing, and repetition) can be incorporated into broader testing that might determine other cognitive functions. Evaluators must remember that language is the medium though which most of these other functions are observed. Therefore, language should be assessed first; if extensive aphasia is present, then only cautious interpretations of other cognitive functions may be given. At present, there are few available objective and standardized measures for testing during the acute phases of disorders such as stroke.
A number of standardized measures are available that provide an inventory of aphasic symptoms. These tests are useful in providing baseline and follow-up assessments to measure progress in treatment, as well as to guide the treatment itself. A fairly general feature of aphasia tests is that individuals without aphasic symptoms should perform with almost no errors on them. Tests are available to measure the extent and severity of language impairments as well as to provide information about functional skills and outcomes. Finally, there are assessments designed specifically to look at quality of life with aphasia.
Treatment team
Because of the various other problems in addition to language that affect most individuals with aphasia, a multidisciplinary team is used in rehabilitation centers for the management of aphasia. Team members, as well as speech-language pathologists, typically include physical and occupational therapists, clinical neuropsychologists, nurses, and social workers who are guided by physiatrists and neurologists. Once discharged from rehabilitation centers, aphasic individuals often continue their treatment by speech-language pathologists in settings such as speech and hearing clinics. Self-help groups and support via the Internet are available as well.
Treatment
Most individuals with aphasia are hospitalized for some period of time for treatment of the condition that has resulted in aphasia. Assessment of the extent and type of language disorder is made during that time, as assessment of the ability to swallow (dysphagia). Early medical intervention is important for lessening the long-term effects of stroke.
Recovery and rehabilitation
To date, no pharmacological treatments for aphasia have proven effective, although a number of drugs (dopaminergic, cholinergic, and neurotrophic) continue to be investigated, usually in conjunction with behavioral treatments for aphasia. Various behavioral treatment approaches for aphasia exist. They are usually characterized dichotomously as restorative (restitutive) or compensatory. The goal of restorative treatments is to reestablish disordered language skills. Goals for compensatory approaches are to develop and train alternative approaches to circumvent the language skills that have been affected by aphasia. Most clinicians use both approaches (often simultaneously) to aid in language recovery. Some examples of restorative approaches include practice of carefully selected syntactic structures, naming drills, or practice using self-selected communication needs such as using the telephone.
Compensatory approaches include training conversational partners to modify their own language and communication skills in ways that make it easier for the aphasic individual to communicate, or teaching aphasic individuals to use a relatively intact language skill such as writing or drawing to substitute for talking. Computerized approaches to both restitutive and compensatory aphasia treatment are increasing. Many clinics offer both individual treatment and group treatment, with the latter offering increased psychosocial support. Many clinics also incorporate family support groups.
Clinical trials
Randomized control trials (RCTs) are rare for the behavioral realm of treatments. Aphasia is no exception. To date, only four RCTs have been completed, with three of the four addressing to the efficacy of treatment. A far greater number of phases I and II studies exist, and investigate the value of language intervention, particularly post stroke. The largest testimony comes from single-case designs and qualitative case studies that agree that treatment has a positive influence on outcome. Only one meta-analysis of significant scope has been completed (Robey, 1998).
Prognosis
The traditional view is that most of the language gains made by aphasic individuals will occur in the first six months following injury, except in persons with global aphasia, who may begin the recovery process later, but are shown to make gains through one year. Significantly, it must be noted that most traditional treatment techniques have been validated using aphasic patients whose period of spontaneous recovery has passed. Some people with aphasia may be able to return to work, although the communicative demands of many occupations may affect employment.
As of the late 1990s, research has begun to focus on recovery across the remainder of the lifespan, and it has become apparent that aphasic individuals continue to make progress, often for years after the precipitating event. The factors that explain very late recovery are not clear and will require scientific observation and study.
Special concerns
Despite the prevalence of aphasia, the disorder is neither well recognized nor well understood. Aphasia's psychosocial and vocational consequences are over-whelmingly devastating, but community understanding is at best limited. Similarly, despite substantial evidence concerning the effectiveness of intervention, skepticism about the value of treatment remains. As a consequence of both of these factors, many aphasic individuals and their families are not well informed about either the disorder or what might be done to alleviate it.
Additionally, although a significant and growing number of individuals in the United States is bilingual, there is a surprising lack of research concerning the effects of speaking more than one language on recovery from aphasia. Finally, current funding for only very limited treatment for aphasia is available via third-party reimbursement.
Resources
BOOKS
Davis, G. A. Aphasology: Disorders and Clinical Practice. Boston: Allyn and Bacon, 2000.
Goodglass, H. Understanding Aphasia. New York: Academic Press, 1993.
Hillis, A. E. The Handbook of Adult Language Disorders. New York: Psychology Press, 2002.
PERIODICALS
Robey, R. R. "A Meta-analysis of Clinical Outcomes in the Treatment of Aphasia." Journal of Speech and Hearing Research 41 (1998): 172–187.
ORGANIZATIONS
Aphasia Hope Foundation. 2436 West 137th St., Leawood, KS 66224. (913) 402-8306 or (866) 449-5894; Fax: (913) 402-8315. http://www.aphasiahope.org.
National Aphasia Association. 29 John Street, New York, NY 10038. (212) 267-2812 or (800) 922-4622. naa@aphasia.org. http://www.aphasia.org.
Audrey L. Holland, PhD