Motor speech disorders are a group of disorders that interrupt the ability of the body to produce speech. There are a variety of causes of these disorders but all involve some level of dysfunction in the ability of the brain to integrate neurological and muscular activities. The ability to produce speech involves a thought and the regulation on airflow and placement of lips and tongue. These activities can be disrupted by conditions that impact the central or peripheral nervous systems that are involved in the planning of motor functions (Vargha-Khadem, Gadian, Copp, Mishkin, 2005). This paper will explore two groups of motor speech disorders: dysarthria, apraxia, and developmental verbal dyspraxia. Causes and differentiating symptoms will be presented.
Dysarthria
Dysarthria is a condition that involves weakness in the muscle function around the mouth (oral musculature). It interferes with the placement of the lips, tongue, and jaw. It is , by definition, a reduced ability to plan the voluntary motor activities needed to produce speech This condition results from damage to the neurological centers that that control the motor speech system. Dysarthria is characterized by an inability to pronounce words that is not necessarily accompanied by an inability to understand language. Dysarthria can affect any of the subsystems of speech including respiration, resonance, prosody, phonation, or articulation. As a result, speech may be unintelligible, unnatural, inefficient, and even inaudible. In some cases, the dysarthria can progress to the degree that all speech is lost. This condition is called anarthria ((Vargha-Khadem, Gadian, Copp, Mishkin, 2005).
Dysarthria should not be confused with speech problems that are the result of structural problems or those that involve that centers of the brain that govern the planning or programming of speech. The problems in dysarthria originate in the cranial nerves, specifically the trigeminal nerve (its motor branch, V), the facial nerve, the glossopharyngeal nerve, vagus nerve, and the hypoglossal nerve (Vargha-Khadem, Gadian, Copp, Mishkin, 2005).
There are various types of dysarthrias They are classified primarily according to the symptoms they present. Spastic dyarthrias are produced when there is damage to both sides of the upper motor neuron. Flaccid dysarthrias involve damage to the lower motor neuron. When there is damage to the cerebellum, an ataxic dysarthria is produced. Unilateral damage to the upper motor neuron can cause a mild dysarthria. If the basal ganglia in damaged, the individual may display a hypokinetic or hyperkinetic dysarthria. Most individuals with dysarthria have a mixed type that results from a traumatic brain injury or some degenerative condition that involves multiple part of the nervous system (Vargha-Khadem, Gadian, Copp, Mishkin, 2005).
Ataxic dysarthria is an acquired condition that is usually a part of other ataxic disorders. Common feature of ataxic dysarthrias are abnormalities in articulation and the timing of speech. ( prosody). There are also notable abnormalities in the rate of speech, modulation, rate of speech, scanning speech, or explosive speech. Dysarthrias also are characterized by irregular stress patterns, vocalic and/or consonantal misarticulations (West; Hesketh; Vail,; Bowen; West,2005).
Apraxia
Apraxia of speech or AOS refers to an acquired disorder that disrupts the ability of the individual to integrate intentional speech with the requisite motor functions. While this condition usually involves the volitional production of speech, it also can be observed in the production of automatic speech (Knollman-Porter, 2008).
The problem in apraxia is the dysfunction in the centers of the brain that plan motor responses. Therefore, individuals know what they want to say but the signal does not travel to the muscle to create the appropriate movement. The individual displays significant problems with sequencing and forming sounds. They may also display groping (Ogar, Slama, Dronkers, Amici, Gorno-Tempini, 2005).. This characteristic feature is displayed by an effort to move the mouth to form the correct sound. This is a trial and error process the causes the individual to speak with long extended sounds, repeated sounds, or silent speak. They may be able to create some sounds correctly on their own but if they try to do so on command, produce the wrong sound. Speech production is difficult and requires great effort. They attempt to correct their own errors and demonstrate significant stress. Unlike those with dysarthria, they have great difficulty initiating speech. An important differentiating characteristic of apraxia is the absence of muscle control issues. The individual can make the correct sound without difficulty physically but cannot plan and therefore execute speech to convey an idea (Knollman-Porter, 2008).
As mentioned, AOS is an acquired condition (Knollman-Porter, 2008). It can occur as the result of a head injury or stroke. It may also result from some degenerative conditions the effect the speech planning centers of the brain. Dyspraxia can also occur at birth or in the early years of development (Maassen, 2002).. Developmental verbal dyspraxia (DVD) or childhood apraxia of speech (CAS) effects a child’s ability to plan and execute speech in the years when language is learned. The characteristics of DVD and CAS are similar to AOS but may have other causes.
Treatment
The first step in the treatment of motor speech disorders involves the completion of an evaluation and assessment. This assessment is designed to provide an exploration of both strengths and weaknesses in function. It in not limited solely to speech and language function but also to other skills and deficits that may affect the individual’s ability to benefit from a particular program. This assessment is completed by trained speech-language pathologists who may be part of a team that includes family and professionals ( ASHA, 2005).
Assessments involve a review of systems including auditory, visual, motor, cognitive, language, and emotional status. History is important in assessing the individual’s ability to respond to treatment. The individual’s preferences are also important in designing this process. A physical examination involves an assessment of both non-speech and speech muscles for tone, strength, steadiness, speed, range and accuracy of movement. Auditory processes are also important. An evaluation of pitch, volume, and tonal quality is necessary. This information is collected through both simulated and natural contexts ( ASHA, 2005).
Because motor speech disorders are neurogenic, they cannot be eliminated by behavioral techniques alone. In some cases, these neuromuscular conditions can affect breathing support and swallowing. Therapists can design exercises that improve or maintain muscle strength and coordination. Individuals can learn to compensate for the dysfunctions or otherwise develop strategies to help themselves (Morgan & Vogel, 2009).
Speech and Language therapists provide exercises that allow the individuals to retrain their brains and mouths to produce sounds. They can then learn to sequence those sounds into words. These exercises require the individual to repeat the sounds for the purpose of correcting mouth movements. Individuals with apraxia learn to correct the pace of speech to allow themselves an opportunity to produce all the necessary sounds ( Morgan & Vogel, 2009). In some cases, individuals simply cannot learn to produce speech sounds voluntarily. In these cases, augmentative devices can be a solution. Other alternatives such as the use of gestures of sign can also be helpful.
