Dysarthria is commonly caused by neurological conditions such as Parkinson’s disease, cerebral palsy, Lou Gehrig’s disease, or late stages of multiple sclerosis. It may also occur after a cerebral vascular accident (stroke), head trauma, tumor, or infection.
Existing at birth or occurring over time, dysarthria is considered a disorder of movement. Symptoms occur due to paralysis, weakness, or incoordination of the muscles that coordinate the production of speech sounds and can be noticed in any of the other factors needed for fluent speech. These include respiration (breathing), phonation (sound produced from the vibration of the vocal cords), resonance (the inflection or tone of voice), articulation (movement of oral structures) and prosody (quality and intensity of voice).
Dysarthria resulting from a stroke is generally broken into two categories based on location in the brain where the damage occurred. Damage to upper motor neurons (UMN) those running from the brain to the spine, results in spastic dysarthria, while damage to the lower motor neurons (LMN) those running from the spine to the muscle, results in flaccid dysarthria.
What is spastic dysarthria?
Meaning “excessive tone,” spastic dysarthria damage can be unilateral (on one side of the body) or bilateral (on both sides of the body). Unilateral damage may be noticed in facial features that droop on the side of the face opposite the side of the brain where the damage occurred. The tongue often moves slowly and has difficulty meeting the weak side of the mouth. The palate, or portion of the oral cavity that forms the roof of the mouth, is usually only minimally affected. The larynx, or muscles of the throat, tends to not be affected so the client’s ability to swallow is usually fine. Prognosis for intelligible speech can be good if therapy is initiated soon after the damage to the brain occurs.
A more debilitating aspect of spastic dysarthria occurs with bilateral damage of the upper motor neurons (UMN). Also known as pseudobulbar palsy, bilateral UMN damage severely affects both the range and rate of movement of the tongue, lips, and jaw. The back and front of the tongue tend to be disproportionately affected, causing different classes of sounds to be distorted. Voice quality may be perceived as “harsh,” sounding almost strangled. The pitch of voice is commonly low with little variation in loudness. It is not uncommon for chewing and swallowing problems to arise. Movement of the palate can be severely reduced, causing excessively nasal speech.
What is flaccid dysarthria?
Flaccid dysarthria is caused by damage to the lower motor neurons (LMN). Symptoms may be seen in reflexive, automatic, or voluntary movement and most commonly arise from a brainstem stroke or condition known as myasthenia gravis. Reflexes become reduced, which in turn shortens or causes atrophy to the muscle over time. If atrophy occurs, muscles may become flabby and have difficulty lifting, reaching, or moving forward. Tiny tremors may also occur, disrupting the fluency of movements, especially in the tongue. Speech production will range in its precision, but sounds requiring the tongue tip (/p/, /t/, and /k/) or sounds needing pressure in the mouth (/s/, /f/) are more likely to be affected.
Damage to the vocal cords will also affect voice production. If one of the vocal cords is paralyzed, the effect on quality of speech depends on the position of the fold when it became paralyzed. More common than a single vocal cord being paralyzed, both vocal cords may be unable to move. If this is the case, a client may have trouble changing pitch or loudness, and the quality of the client’s voice will often be breathy. Other characteristics of bilateral vocal cord paralysis are audible breaths when inhalating and speaking in short phrases.
Another area of concern for patients with lower motor neuron damage is that of dysphagia, or difficulty with swallowing. Injuries to the brainstem are commonly related to the ability to protect the airway. Because brainstem strokes commonly cause flaccid dysarthria, many patients with lower motor neuron damage develop dysphagia.
If both upper and lower motor neurons are involved, a patient is diagnosed with Amyotrophic Lateral Sclerosis (ALS), or Lou Gehrig’s disease, usually occurring in the fifth decade of life, ALS has various symptoms depending on the type and extent of neurons affected.
How can speech therapy help?
Speech therapists currently provide several options for alternative communication and feeding. Because each patient is unique, professionals design a therapy program to best suit the individual’s immediate needs. If deficits exist in both speech and swallowing, the swallowing issues will be addressed first to establish proper nutrition. If an individual is strong, both areas can be addressed at the same time. It is important to remember that differences in symptoms and therapy potential will occur depending on site and severity of the damage in the brain.