Dysarthria is a motor speech disorder resulting from neurological injury of the motor component of the motor-speech system and is characterized by poor articulation. Any of the speech subsystems can be affected, leading to impairments in intelligibility, audibility, naturalness, and efficiency of vocal communication.
Neurological injury due to damage in the central or peripheral nervous system may result in weakness, paralysis, or a lack of coordination of the motor-speech system, producing dysarthria. These effects in turn hinder control over the tongue, throat, lips or lungs for example, and swallowing problems (dysphagia) are often present.
The term dysarthria does not include speech disorders from structural abnormalities, such as cleft palate, and must not be confused with apraxia, which refers to problems in the planning and programming aspect of the motor-speech system.
Cranial nerves that control these muscles include the trigeminal nerve's motor branch (V), the facial nerve (VII), the glossopharyngeal nerve (IX), the vagus nerve (X), and the hypoglossal nerve (XII).
Dysarthrias are classified in multiple ways based on the presentation of symptoms. Specific dysarthrias include spastic (resulting from bilateral damage to the upper motor neuron), flaccid (resulting from bilateral or unilateral damage to the lower motor neuron), ataxic (resulting from damage to cerebellum), unilateral upper motor neuron (presenting milder symptoms than bilateral UMN damage), hyperkinetic and hypokinetic (resulting from damage to parts of the basal ganglia, such as in Huntington's disease or Parkinsonism), and the mixed dysarthrias (where symptoms of more than one type of dysarthria are present). The majority of dysarthric patients are diagnosed as having 'mixed' dysarthria, as neural damage resulting in dysarthria is rarely contained to one part of the nervous system - for example, multiple strokes, traumatic brain injury, and some kinds of degenerative illnesses (such as amyotrophic lateral sclerosis) usually damage many different sectors of the nervous system.
Dysarthria may affect a single system; however, it is more commonly reflected in multiple motor-speech systems. The etiology, degree of neuropathy, existence of co-morbidities, and the individual's response all play a role in the effect the disorder has on the individual's quality of life. Severity ranges from occasional articulation difficulties to verbal speech that is completely unintelligible.
Individuals with dysarthria may experience challenges in the following:
- Vocal quality
- Breath control
Examples of specific observations include a continuous breathy voice, irregular breakdown of articulation, monopitch, distorted vowels, word flow without pauses, and hypernasality.
The causes of dysarthria can be many, including toxic, metabolic, degenerative diseases (such as Parkinsonism, ALS, Huntington's Disease, Niemann Pick disease, Ataxia etc.), traumatic brain injury, or thrombotic or embolic stroke. These result in lesions to key areas of the brain involved in planning, executing, or regulating motor operations in skeletal muscles (i.e. muscles of the limbs), including muscles of the head and neck (dysfunction of which characterises dysarthria). These can result in dysfunction, or failure of: the motor or somatosensory cortex of the brain, corticobulbar pathways, the cerebellum, basal nuclei (consisting of the putamen, globus pallidus, caudate nucleus, substantia nigra etc.), brainstem (from which the cranial nerves originate), or the neuro-muscular junction (in diseases such as Myasthenia Gravis) which block the nervous system's ability to activate motor units and effect correct range and strength of movements. Causes - By Mayo Clinic staff Dysarthria is caused by difficulty or inability to move the muscles in your mouth, face or upper respiratory system that control speech. Conditions that may result in dysarthria include, in addition to those above:
- Brain tumor;
- Cerebral palsy;
- Guillain-Barre syndrome;
- Head injury;
- Lyme disease;
- Multiple sclerosis;
- Parkinson's disease;
- Wilson's disease;
- Intercranial Hypertension (formerly known as Pseudotumor Cerebri);
- Tay-Sachs, and Late Onset Tay-Sachs (LOTS), disease
Articulation problems resulting from dysarthria are treated by speech language pathologists, using a variety of techniques. Techniques used depend on the effect the dysarthria has on control of the articulators. Traditional treatments target the correction of deficits in rate (of articulation), prosody (appropriate emphasis and inflection, affected e.g. by apraxia of speech, right hemisphere brain damage, etc.), intensity (loudness of the voice, affected e.g. in hypokinetic dysarthrias such as in Parkinson's), resonance (ability to alter the vocal tract and resonating spaces for correct speech sounds) and phonation (control of the vocal folds for appropriate voice quality and valving of the airway). These treatments have usually involved exercises to increase strength and control over articulator muscles (which may be flaccid and weak, or overly tight and difficult to move), and using alternate speaking techniques to increase speaker intelligibility (how well someone's speech is understood by peers).
More recent techniques based on the principles of motor learning (PML), such as LSVT (Lee Silverman Voice Treatment) Speech therapy and specifically LSVT may improve voice and speech function in PD. for Parkinson's, aim to retrain speech skills through building new generalised motor programs, and attach great importance to regular practice, through peer/partner support and self-management. Regularity of practice, and when to practice, are the main issues in PML treatments, as they may determine the likelihood of generalisation of new motor skills, and therefore how effective a treatment is.
Augmentative and Alternative Communication (AAC) devices that make coping with a dysarthria easier include speech synthesis software and text-based telephones. These allow people who are unintelligible, or may be in the later stages of a progressive illness, continue to be able to communicate without the need for fully intelligible speech. Some cases of dysarthria, as in children are of no known causes. It is a speech motor disorder causing high pitch and tone, mis pronunciation of words and fast talking. Children benefit from a speech and language therapist to help them slow down, practice beginning and end sounds of words. It is not genetic. Children sometimes cannot chew properly,thus over stuffing their mouths since there is no sensation of fullness. Early in childhood, some show signs of dysarthria but it takes years to get the correct diagnosis. A case of a 4 yo diagnosed December 2009 in which in hindsight, the pieces came together. Late talker, seemed to have acid reflux ( projectile vomiting), smile was irregular and always talked in "gibberish". Children also do well when introduced to others their age to socialize and "pick up" correct word usage. This 4 yo in particular always sounded "deaf" to her parents since she always talked loud and off key. Word books could be helpful for hard to understand words, but require training on both ends( the parent and child). Speech therapy is very beneficial to the child. After a year of SLP; the 4 yo is talking more but has difficulty with ending sounds and slow speaking. She sounds different than a typical 4 yo but has made remarkable progress. A hearing test as well as any other should be done to rule out hearing loss or a developmental delay. Dysarthria in children is classified as a learning disability. Before entering a school program, a parent should and must have all information on the child, the treatment plan and request weekly SLP sessions as well as an Individualized Education Plan (IEP) in place to ensure the child gets the correct education and assistance if needed. Dysarthria in children without a genetic or brain disorder are more common than first believed and the least attention as to why this disorder affects an other wise health child.