|Classification and external resources|
Dysarthria is a motor speech disorder resulting from neurological injury, characterised by poor articulation (cf. aphasia: a disorder of the content of speech). Any of the speech subsystems (respiration, phonation, resonance, prosody, articulation and movements of jaw and tongue) can be affected.
Dysarthric speech is due to some disorder in the nervous system, which in turn hinders control over, for example, the tongue, throat, lips or lungs. Swallowing problems (dysphagia) are often present.
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).
Dysarthias 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 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.
The causes of dysarthria can be many, including toxic, metabolic, degenerative diseases (such as Parkinsonism, ALS, Huntingtons 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 (ie. muscles of the limbs), including muscles of the head and neck (dysfunction of which characterises dysarthia). These can result in dysfunction, or failure of: the motor or somatosensory cortex of the brain, corticobulbar pathways, the cerebellum, basal nuclei(comprising 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.
Articulation problems resulting from dysarthia are treated by speech language pathologists, using a variety of techniques. Techniques used depend on the effect the dysarthia has on control of the articulators. Traditional treatments target the correction of deficits in rate (of articulation), prosody (appropriate emphasis and inflection, affected eg. by apraxia of speech, right hemisphere brain damage, etc.), intensity (loudness of the voice, affected eg. in hypokenetic 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 Therapy) 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.