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Dysarthria

Definition

Dysarthria is a group of speech impairments due to weakness, incoordination, spasticity, rigidity, or irregular movements caused by damage to the nervous system.

Description

Speech abilities depend on the coordinated function of muscles of respiration, phonation (larynx), and articulation. These functions are controlled by a complex neural circuitry involving the structures and pathways of the peripheral nervous system (cranial and spinal nerves) and central nervous system (cerebral cortex, basal ganglia, substantia nigra, cerebellum, brainstem). Damage to any portion of the speech neural circuitry can lead to dysarthria. As a result, speech may be distorted and difficult to understand. Dysarthria is frequently accompanied by dysphagia, or swallowing difficulty, as similar neural circuits are necessary for swallowing function. Depending on which portion of the nervous system is affected, dysarthria can be accompanied by other speech, language, motor and sensory disturbances. Dysarthria can occur in adults and children who have neurologic conditions affecting the speech circuitry.

Causes and symptoms

Many neurologic etiologies that affect the speech neural circuitry can lead to dysarthria. Among the most common etiologies are stroke, degenerative conditions (e.g., Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, cerebellar degeneration, multiple sclerosis), trauma, cerebral palsy, tumor, infections, and toxic conditions. Because dysarthria can arise from so many different neurologic conditions, the prevalence of the disorder is difficult to estimate.

The symptoms of dysarthria vary depending upon which portion of the neural circuitry is damaged. Articulation may be slurred, imprecise, distorted, or irregular. The resonance quality of speech may be hypernasal (over nasally sounding) or hyponasal (under nasally sounding). The voice may be breathy, strained, hoarse, or strangled to the point of stopping. Selective dysphonia (strained or breathy voice quality) can be observed. The prosody or melody of speech may be flattened, excessive, or choppy. The rate of speaking is usually slowed, but some individuals may actually speak at an excessive rate. Respiration for speech may be weak or forced. Tremor, spasms, or excessive movements of the speech muscles may disrupt the flow of speaking. Different combinations of symptoms can lead to significant loss of speech intelligibility (how easily speech is understood). Patterns of these symptoms tend to be observed in relation to the part of the nervous system that is damaged.

Diagnosis

A physician will perform a clinical neurological examination to determine a diagnosis in individuals with suspected neurologic disease. When an accompanying speech disorder is noted, the physician will refer the patient to a speech-language pathologist trained in the administration of speech examination protocols to identify the pattern of dysarthria and determine a course of treatment if warranted. Although most dysarthria tests depend on the clinician's perceptual analysis and judgment of the patient's speech characteristics, some acoustic and physiologic measurements can be completed using computerized analyses. Clinicians evaluate patterns of speech characteristics related to articulation, resonance, phonation, respiration, and prosody to determine a course of intervention. Assessment of dysarthria, which occurs in acute through chronic stages of the neurologic condition, takes one to two hours to complete.

Treatment

Treatments provided by physicians that may improve aspects of dysarthria include pharmacologic treatments for neurologic conditions, surgical intervention (e.g., injection of botulinum toxin into the vocal folds), or prosthetic management (for example, palatal lift, a prosthesis used to improve speech for a patient with an incompetent soft palate). Patients with dysarthria often work with a speech-language pathologist who will use behavioral methods to alleviate the consequences of dysarthria for communication. When patients have a neurologic condition from which recovery is anticipated (e.g., stroke), clinicians will use drills and practice with speech activities to restore speech skills or identify strategies to improve speech intelligibility. In degenerative neurologic conditions, when it often becomes impossible to rehabilitate speech, patients with dysarthria may adopt alternative and augmentative communication strategies including writing, communication pointing boards, computers, or speech-generation devices to compensate for the severe speech impairment.

Prognosis

The prognosis for recovery of dysarthria relates to the nature of the neurologic disorder that has caused the disease. When patients develop degenerative neurologic conditions, speech is likely to deteriorate as well. When the patient has a static or recovering neurologic condition (e.g., stroke), some improvement in speech abilities is likely depending on the extent of the nervous system injury.

Health care team roles

Nursing and medical staff providing medical care for individuals with dysarthria implement strategies recommended by speech-language pathologists to foster communication with patients. The rehabilitation team (e.g., physical therapist, occupational therapist, physiatrist, social worker) assists with neurological recovery and implements strategies to maximize communication skills.

Prevention

The way to prevent dysarthria is to prevent the neurologic event that causes dysarthria.

KEY TERMS

Articulation—The pronunciation of speech sounds.

Central nervous system—Portions of the nervous system within the confines of the meninges and bones.

Dysphagia—Swallowing difficulty.

Dysphonia—Hoarse, breathy, or strained voice.

Etiology—The cause or causes of a disease or condition.

Peripheral nervous system—Portions of the nervous system that exit the meninges; the nerves.

Phonation—Sound that emanates from the larynx; voice.

Prosody—Intonation and rhythm of speech.

Resonance—The nasal quality of speech.

Resources

BOOKS

Duffy, J.R. Motor speech disorders. St. Louis: Mosby, 1995.

Weiner, W.J., and Goetz, C.G., eds. Neurology for the Non-Neurologist. Philadelphia: Lippincott, Williams, & Wilkins, 1999.

ORGANIZATIONS

American Academy of Neurology. 1080 Montreal Avenue, St. Paul, MN 55116. (651) 695-1940. 〈http://www.aan.com〉.

American Speech-Language-Hearing Association. 10801 Rockville Pike, Rockville, MD 20852. (800) 638-8255. 〈http://www.asha.org〉.

National Institute of Deafness and other Communicative Disorders: Health Information: Aphasia. National Institutes of Health, 31 Center Drive, MSC 2320, Bethesda, MD 20892-2320. 〈http://www.nidcd.nih.gov/health/pubs_vsl/〉.

National Parkinson Foundation. Bob Hope Parkinson Research Center, 1501 N.W. 9th. Avenue, Bob Hope Road, Miami, FL 33136-1494. (305) 547-6666. (800) 327-4545. 〈http://www.parkinson.org〉.