Understanding Dysarthria: A Neuromuscular Speech Disorder

Dysarthria is a neuromuscular disorder that prevents the muscles in the vocal tract from working properly. This disorder most commonly takes place within the oral cavity of the vocal tract. It affects the articulators in a way that can create several possible symptoms noticeable in a person's speech. The type and severity of symptoms that occur depend on the location of the damage or lesion in the nervous system. Dysarthria is seen in many stroke and trauma victims, but can also be caused by various other diseases and disorders such as Parkinson's disease, cerebral palsy, and muscular dystrophy. No matter what the cause or etiology, there are some very common symptoms associated with the majority of patients who have been diagnosed with this disorder.

Muscle Weakness or Paralysis - This symptom occurs when a person has damage in the area of their brain where their lower motor neurons, muscle fibers, and myoneural (myo=muscle) junctions are located. This type of damage causes weakness or paralysis of muscle contractions. This is known as flaccidity and it limits the function of a person's articulators and muscles necessary for speech. Sometimes, depending on the type of disease or disorder and the severity of the condition, a patient may experience complete paralysis of muscle contractions. Muscular dystrophy is the most common disease known to do this. It is a progressive disease that starts during childhood, which deteriorates muscle fibers, and ultimately can result in paralysis.

Reduced Range of Movement - This symptom occurs when there is a lesion in the area of the brain where the upper motor neurons are located. This type of damage can cause a condition called spasticity to occur. This means that the person will experience hyperactive reflexes and disturbances when attempting to control voluntary movements. This can become an issue with speech because spasticity can limit a person's ability to completely produce articulatory gestures. For example, someone with this condition may attempt to produce a sound, which requires them to elevate their tongue, but they may not be able to fully lift it, due to their limited range of movement.

Involuntary Movement - This symptom usually occurs when there is damage to the portion of the brain known as the basal ganglia. It causes a person's muscles to move involuntarily. When these involuntary movements take place in the vocal tract, the size and shape of the tract are altered causing articulation errors.

Poor Coordination - This symptom usually occurs when there is a lesion in the part of the brain known as the cerebellum. This is known to regulate different characteristics of bodily movements such as direction, timing, force, speed, and range of movements, particularly rapid ones. Articulation of speech sounds is a very rapid process, therefore, if there is damage to this area of the brain, it can affect the way the person is able to control the muscles of their oral cavity and precisely and accurately articulate their words when speaking.

Dysarthria is a very frustrating disorder to live with and requires adjustments in various areas of life, but therapy is available. Speech-Language Pathologists are trained to help support, diagnose, treat, and teach the patients compensatory strategies to allow more effective communication.

Source:
Silverman, Franklin H. Essentials of Speech, Language, and Hearing Disorders. Cincinnati: Atomic Dog, 2003.