What is Dysarthria?
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 speech musculature and can be noticed in any of the components required for fluent speech. These include respiration (breathing), phonation (sound produced from the vibration of the vocal folds), 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 site of lesion. 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.
Meaning “excessive tone,” spastic dysarthria damage can be unilateral or bilateral. Unilateral damage may be noticed in facial features that droop on the side of the face opposite the site of the brain lesion. The tongue often moves slowly and has difficulty meeting the weak side of the mouth (the side opposite the lesion). The palate, or portion of the oral cavity that forms the roof of the mouth, is usually affected only minimally. The larynx tends to be intact so swallow function is often preserved. Prognosis for intelligible speech can be good if therapy is initiated within a brief period of time after onset.
A more devastating side of spastic dysarthria occurs with bilateral UMN damage. Also known as pseudobulbar palsy, bilateral UMN damage severely affects both range and rate of articulation movement. The back and front of the tongue tend to be disproportionately affected, causing different classes of sounds to be distorted. Voice quality may appear “harsh,” sounding almost strangled. 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.
Caused by any disease that affects a part of the motor unit, LMN damage is known as flaccid dysarthria. 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 intraoral pressure (/s/, /f/) are more susceptible to error.
Damage to the vocal fold will also affect voice production. If one of the folds is paralyzed, quality of speech depends on the position of the fold when it became paralyzed. More common than a single fold being paralyzed, both may be unable to move. If this is the case, a patient may have trouble changing pitch or loudness, and voice will often be breathy. Other characteristics of bilateral vocal fold paralysis are audible inhalation 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 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 occuring in the fifth decade of life, ALS has various symptoms depending on the type and extent of neurons affected.
Speech therapists at the Center for Speech, Language and Occupational Therapy, Inc. 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 lesion.