Abstract
Altered speech, language, and cognitive dysfunction result from a direct insult to the brain due to various neurologic disorders. Distinctive patterns of language use have been associated with certain neurologic conditions. In the majority of individuals, the left brain contains centers of language, whereas the right brain has a distinct role in cognitive performance. Language is the communication system for the dissemination of thoughts, emotions, and beliefs. The use of language depends on receptive and expressive abilities. Receptive language is the ability to understand words; expressive language is the ability to produce words. The verbal or oral output of language is referred to as speech. Disorders of speech occur when there are dysfunctions in the key elements of speech, including sound, articulation, phonologic errors, intelligibility, stimulability, fluency, voice, and resonance. Cortical neuroplasticity has a significant role in language recovery following neurologic injury and can be facilitated by behavioral speech and language therapy. Recent research has suggested that by complementing traditional therapies with neurostimulation techniques, functional gains after neurologic injury may be enhanced.
Keywords
aphasia, apraxia, constraint-induced aphasia treatment, direct transcranial direct current stimulation (tDCS), dysarthria, dysphonia, transcranial magnetic stimulation (TMS)
| Synonyms | |
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| ICD-10 Codes | |
| R47.01 | Aphasia |
| R49.0 | Dysphonia |
| R47.1 | Dysarthria and anarthria |
| R47.81 | Other voice and resonance disorders |
| I69.320 | Aphasia following cerebral infarction |
Definitions
A summary of the speech and language disorders described in this chapter is presented in Table 155.1 .
| Disorder | Definition |
|---|---|
| Aphasia | Language processing disturbance that can involve the expression of language, the comprehension of language, or both. Word-finding errors and difficulty in understanding language are classic indicators of aphasia. |
| Dysarthria | Group of motor speech disorders associated with muscle paralysis, weakness, or incoordination. Dysarthria is often manifested as slurred speech and does not involve language (receptive or expressive) processes. |
| Apraxia of speech | Motor speech disorder disrupting the motor programming of the volitional movements for speech. Individuals struggle to position articulators (i.e., lips, tongue) correctly. Apraxia can occur without muscle weakness or impairments in receptive and expressive language. |
| Dysphonia | Faulty or abnormal phonation (voice production). Vocal quality may sound hoarse, harsh, strained, or breathy. |
Aphasia is an acquired neurogenic impairment in language processing that can disrupt the modalities of language, including speaking, listening, reading, and writing. An individual with aphasia has sustained a primary insult to the brain in the area governing language, which most commonly is the left hemisphere. Aphasia occurs in 21% to 38% of cases of acute stroke and is associated with high morbidity and mortality as well as a heavy financial burden. Aphasia also results from conditions other than stroke, such as tumors and head trauma, and must be differentiated from motor or sensory dysfunction, psychiatric illness, confusion, or general intellectual impairment. In the United States, there are approximately 100,000 new cases of aphasia per year, the majority being women 65 years of age and older. Primary progressive aphasia is a term reserved for subtle, insidious, progressive language impairments associated with frontotemporal dementia. In primary progressive aphasia, there is relative preservation of other mental and cognitive functions for at least the first 2 years of the condition.
Aphasia is classified into subtypes according to the ability to produce, understand, and repeat language. The ability to produce language is assessed in terms of fluency, defined as the rate of speech and the amount of effort required to produce speech. Each subtype of aphasia is associated with a specific profile of language ability and disability ( Table 155.2 ). An individual with Wernicke aphasia produces fluent language, has impaired auditory comprehension, and has poor repetition skills. In contrast, Broca aphasia is characterized by nonfluent language, relatively intact auditory comprehension, and poor repetition skills.
| Aphasia Type | Predicted Lesion Site | Comprehension | Fluency | Repetition |
|---|---|---|---|---|
| Broca | Inferior frontal gyrus; Brodmann area | Relatively intact | Nonfluent | Poor |
| Wernicke | Posterior superior temporal gyrus; Brodmann area | Impaired | Fluent | Poor |
| Conduction | Superior marginal gyrus and underlying white matter (arcuate fasciculus) | Relatively intact | Fluent | Poor |
| Transcortical motor | Anterior and superior to Broca area (watershed area) | Relatively intact | Nonfluent | Good or less impaired than spontaneous speech |
| Transcortical sensory | Posterior and inferior to Wernicke area (watershed area) | Impaired | Fluent | Good |
| Transcortical mixed (isolation) | Anterior and posterior association areas (watershed areas) | Impaired | Nonfluent | Less impaired than spontaneous speech |
| Anomic | Angular gyrus or anywhere in the left hemisphere | Relatively intact | Fluent | Good |
| Global | Left frontal, parietal, and temporal lobes | Impaired | Nonfluent | Poor |
Motor speech disorders, which include apraxia and dysarthria, result from neurologic impairment affecting motor planning, neuromuscular control, or execution of speech. Apraxia of speech is a neurologic speech dysfunction characterized by an impaired ability to plan or program the sensorimotor commands required for directing volitional activities; it results in phonetically and prosodically normal speech and can occur without muscle weakness or impairments in receptive and expressive language. Apraxia of speech is a distinct disorder, although some of its symptoms can coexist in the presence of dysarthria and aphasia.
Dysarthria, a group of motor speech disorders resulting from damage to the central or peripheral nervous system, affects 10% to 65% of individuals with acquired brain injury; the degree depends on the type, extent, and duration of injury. Dysarthria results from weakness, paralysis, or lack of coordination of the muscles affecting speech, resulting in an impairment of articulation, respiration, resonance, and phonation (voice production). Dysarthria can be divided into subtypes according to the speech characteristics and underlying pathophysiologic process. The various subtypes of dysarthria described include flaccid, spastic, ataxic, hypokinetic, hyperkinetic, and mixed. Dysarthric speech patterns resulting from neurogenic speech disorders should be differentiated from those resulting from structural problems (such as cleft palate or postlaryngectomy status) or psychogenic disorders. Anarthria is the extreme form of dysarthria in which an individual is entirely incapable of producing articulated speech. Individuals who present with dysarthria can often concomitantly exhibit dysphagia, or impaired swallowing, which can be expected due to the overlap of structures and functions used in speaking and swallowing.
Dysphonia is faulty or abnormal phonation (voice production). Phonation is a complex phenomenon regulated by cranial and spinal nerves that innervate muscles and functions controlling speech and voice production. Although prevalence rates are not well established, dysphonia is common in any condition causing abnormal motion of the vocal cords or lack of coordination of breathing and speaking. These conditions often include brain stem stroke, Parkinson disease, amyotrophic lateral sclerosis, Guillain-Barré syndrome, myasthenia gravis, spastic dysphonia, and multiple sclerosis, among others, as well as secondary processes that alter the structure or function of the vocal cords, including vocal abuse (such as excessive talking, screaming, or smoking), trauma (traumatic or prolonged intubation, arytenoid dislocation), status post–laryngeal surgery, and a variety of disorders (laryngeal cancer, reflux laryngitis). Dysphonia is distinguished from dysarthria in that dysphonia involves only the sound of the voice, whereas dysarthria involves the overall sound of speech, including resonance and articulation.
Symptoms
Individuals with aphasia often complain of difficulty in the formulation or interpretation of language, specifically speaking, reading, writing, or understanding speech. They often report word-finding difficulties and can become frustrated by this. Some individuals, however, are unaware of their deficits. Individuals who solely have a motor speech disorder (e.g., dysarthria, dysphonia, or apraxia of speech) have no impairments in word finding and report no difficulties with reading, writing, or auditory comprehension but complain primarily of difficulty in producing intelligible speech. Aphasia develops most commonly after left hemispheric involvement even in people who are left-handed, whereas neglect, visuospatial impairments, and other cognitive syndromes are demonstrated more commonly with right hemispheric involvement.
Physical Examination
During the physical examination it is important to attend to the various elements of speech, language, and cognition including speech intelligibility, vocal quality, language content, fluency, and auditory comprehension. Deficits in these areas may warrant referral to a speech and language pathologist for further evaluation, testing, and recommendations for treatment. In the rehabilitation setting, the functional independence measure is widely used to assess various functional abilities including communication. Typical physical examination findings are described further on for the four main categories of speech and language disorders.
Aphasia
Findings indicative of aphasia vary according to the location and size of the brain lesion (see Table 155.2 ). A characteristic sign of aphasia is difficulty in comprehending language (spoken, gestural, or written). This type of aphasia is generally termed Wernicke aphasia . Significant impairment can be characterized by difficulty in following simple commands; milder impairments may be obvious only during lengthy or complicated messages. Broca aphasia generally refers to a predominant dysfunction in verbal expression (difficulty in producing meaningful verbal output), which may be manifested as a total loss of language with the production of only jargon (multiple whole-word substitutions) or meaningless sounds. A person with less severe aphasia may be able to express basic wants and needs but have difficulty in expressing complex ideas in conversation. Paraphasias, or naming errors, constitute a classic symptom of aphasia. Phonemic paraphasias involve the substitution, addition, or omission of target sounds (phonemes). An individual may say “bable” for “table.” A semantic paraphasia occurs when an individual produces a word related in meaning to the target word (i.e., “fork” for “spoon”). The severity of impairment can vary for each modality of language (listening, reading, writing, recognition of numbers, and gesturing). Aphasia, then, is a primary disorder in the area of language, and is not a result of decreased auditory or visual perceptual skills, disordered thought processes, impaired motor programming, or weakness or incoordination of the speech musculature.
Apraxia of Speech
Apraxia, a disorder of higher motor cognition, is a frequent sequela of left hemispheric stroke. The most common sign of apraxia of speech is a struggle or effortful groping to speak. This struggle is a direct result of the difficulty in finding the correct position of the articulators (i.e., lips, tongue). Apraxic speech is often halting and may contain sound substitutions, consonant and vowel distortions, omissions, additions, and repetitions. The individual is aware of his or her speech errors and will attempt to self-correct them, with varying degrees of success. Severe forms of apraxia of speech may result in the inability to produce even simple words. Interestingly, most people with apraxia of speech can produce common everyday phrases or sayings (e.g., How are you? Have a nice day. Thank you. ) without error.
Nonverbal oral apraxia, which often coincides with apraxia of speech, is the inability to imitate or to follow commands to perform volitional movements with the mouth or tongue. Apraxia of speech is not caused by muscle weakness, decreased tone, or incoordination, nor is it the result of linguistic disturbances, as in aphasia. Sound-level errors in apraxia of speech are thought to result from difficulty with motor execution and not with the selection of phonemes found in aphasia. Apraxia of speech differs from dysarthria in that it is not a result of paresis or paralysis or the uncoordinated movements of articulatory muscles. Apraxia of speech is believed to reflect a disturbance in the planning and programming of movements used for speech. Errors in apraxia of speech are characteristically highly irregular, in contrast to dysarthric speech errors, which are typically consistent and predictable.
Dysarthria
In dysarthria, speech is often characterized as being slurred, with the predominant dysfunction being distortions of speech sounds. Dysarthria may also be characterized by changes in the rate, volume, and rhythm of speech. Findings and degrees of involvement vary greatly, depending on the pathophysiologic mechanism affected. Table 155.3 presents an overview of the classification of dysarthria by type, anatomic localization of insult, and anticipated motor deficit.
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