This document discusses neurogenic voice disorders. It reviews the anatomy and physiology of the nervous system related to voice production. Damage to lower motor neurons can cause flaccidity of the vocal folds, while upper motor neuron lesions can cause spasticity. Various cranial nerves like the vagus, accessory, and hypoglossal nerves also affect voice. Lesions of the recurrent laryngeal nerve or superior laryngeal nerve impact vocal fold function. Different types of dysarthrias are then outlined, including their causes, symptoms, and treatment approaches.
2. Review of the Nervous System
Review your motor speech and anatomy/physiology notes.
Neurotransmitter issues in the CNS can cause hypo- and
hyperkinetic dysarthrias.
Spasticity of vocal folds results from UMN lesions
Flaccidity of VFs and VF paralysis result from LMN lesions
The PNS cranial nerves can have an effect on the voice if
they are damaged:
IX (Glossopharyngeal)—taste, sensation, innervation of pharynx
X (Vagus)—SLN and RLN branches affect sensory and motor
systems related to the pharynx, larynx, and respiratory
structures
XI (Spinal Accessory)—resonance/respiration
XII (Hypoglossal)—resonance and quality of the voice;
positioning of the larynx and tongue
3. SLN and RLN
SLN innervates the
cricothyroid muscles. Recall
that CT contraction lengthens
the VFs and increases pitch
and contribute to VF
adduction.
RLN innervates the
thyroarytenoid, lateral
cricoarytneoid,
transverse/oblique arytenoids,
and the posterior
cricoarytenoid muscles.
5. Flaccid Dysarthria
Disorder Cause Effects Treatment
Bilateral vocal fold
paralysis
Lesions to Vagus
nerve
VFs paralyzed in
adducted or
abducted position
Medical and/or
surgical
Unilateral vocal fold
paralysis
Surgical trauma to
left RLN, also viral
infections, smoking
Aphonia, monotone,
hoarse/breathy
voice, pitch breaks,
vocal hyperfunction
Voice therapy;
perhaps surgery
Cricothyroid
paralysis
Viral infection of
SLN
Difficulty with pitch
change; breathiness
Resolves in time;
voice therapy helps
Myasthenia Gravis Antibodies block
acetylcholine from
binding to muscles
Dysphonia and
voice fatigue;
weakness increases
with use
Medical. SLP may
recognize symptoms
and refer; could
monitor symptoms
Guillain-Barre
Syndrome
Body’s immune
system attacks
nerves
Possibly dysarthric
speech and weak
voice
Focus on clear
speech and safe
swallowing
6. Unilateral Upper Motor Neuron
Dysarthria
Often due to unilateral lesions in the CNS,
caused by CVAs, tumors, or trauma.
Symptoms include a harsh, strained voice
that may be accompanied by reduced
loudness.
Good breath support is an essential form
of voice therapy for these patients.
7. Hypokinetic Dysarthria
Occurs when there is not enough dopamine to regulate
basal ganglia functioning = Parkinson’s disease.
Physical manifestations include rigidity, bradykinesia,
limited range of motion, and tremor.
Voice symptoms include decreased loudness, breathy
voice, monotone, rapid rushes of speech, and
soft/imprecise consonants.
Bowed vocal folds accompanied by respiration
difficulties may accompany voice symptoms.
Treatments include the Lee Silverman Voice Treatment
program for increased loudness, quality, and
intelligibility. The Pitch Limiting Voice Treatment also
has good results.
8. Hyperkinetic Dysarthria
Disorder Cause Effects Treatment
Huntington’s
Disease
Overabundance of
dopamine
Jerky, irregular
bursts of loud voice;
strained/strangled
voice; monopitch;
poor breath control.
Behavioral voice
therapy in early
stages (slower
speech and easier
voice production)
Adductor Spasmodic
Dysphonia
Generally
neurogenic
Strained, tight voice
produced when VFs
(true and sometimes
false) adduct during
phonation
Vocal hygiene
therapy, including
easy voice
production); Botox
injections
Abductor Spasmodic
Dysphonia
Generally
neurogenic
Intermittent aphonia Botox, possible
voice therapy
Essential tremor Neurogenic Alternating changes
in pitch; shaky voice
quality
Behavioral voice
therapy-talk less
loudly with a higher
pitch and shortened
vowel duration
9. Mixed Dysarthrias
Amyotrophic Lateral Sclerosis (ALS) and
Multiple Sclerosis (MS) are examples.
A hoarse voice due to hyperfunction is
typical of both of these disorders. Breath
support and easy onset of voice is
recommended.
Voice symptoms associated with
Traumatic Brain Injuries (TBIs) are
typically treated behaviorally.
10. Mixed Dysarthrias
Amyotrophic Lateral Sclerosis (ALS) and
Multiple Sclerosis (MS) are examples.
A hoarse voice due to hyperfunction is
typical of both of these disorders. Breath
support and easy onset of voice is
recommended.
Voice symptoms associated with
Traumatic Brain Injuries (TBIs) are
typically treated behaviorally.
Editor's Notes
In this unit we will begin our discussion of neurogenic voice disorders. We will explore types of dysarthrias and the effects that the diseases and disorders associated with these dysarthrias have on voice production.
Because this is a graduate level course, I know that you have all had an undergraduate anatomy and physiology class, and many of you may have already taken a motor speech class at the grad level. For this unit you will want to review your notes on the nervous system. Make sure you are familiar with the Central and Peripheral Nervous Systems as well as the functions of the upper and lower motor neurons. The cranial nerves which are most important to voice disorders include the Glossopharyngeal, Vagus, Spinal Accessory, and Hypoglossal nerves. You should understand how lesions to these nerves might impact a person’s ability to produce good voice. Let’s take a look at the next slide to discuss what is arguably the most important cranial nerve for voice production, the vagus nerve.
You will recall that there are two parts to the Vagus nerve: the superior laryngeal nerve and the recurrent laryngeal nerve. Each of these nerves serve different purposes for voice production. The superior laryngeal nerve or SLN innervates the cricothyroid muscle, which you will recall is the primary muscle of pitch change. Nearly every other major muscle of the larynx is innervated by the recurrent laryngeal nerve, or RLN. Note on the picture that the left branch of the RLN loops around the aortic arch. If a patient undergoes heart surgery and has a subsequent weak voice or paralyzed vocal folds, there is a good chance that a lesion to the RLN occurred during the surgery.
There are many types of dysarthria that can occur due to neurogenic diseases. In the slides that follow, I will highlight neurogenic disorders that result in dysarthrias and their effects on voice production.
In this slide I have included the major disorders of voice related to flaccid dysarthria. Remember that flaccid dsyarthria means that there is weakness or paralysis of the musculature. Let’s start with vocal fold paralysis. Vocal fold paralysis comes in two types: bilateral and unilateral. The bilateral form is obviously the most debilitating. If the folds are stuck in the abducted position, then there is a choking hazard. On the other hand, if the folds are stuck in the adducted position, breathing may be compromised. Treatment is mostly medical or surgical and can even include tracheotomy if breathing is impaired. Unilateral paralysis is usually less severe and results from infections and smoking, though surgical trauma to the left recurrent laryngeal nerve is the most common cause. Voice therapy is usually warranted focusing on good vocal hygiene and compensatory strategies. Surgical procedures like thyroplasty or injections are also used to treat unilateral vocal fold paralysis. Cricothyroid paralysis can occur when there is an infection in the superior laryngeal nerve. Difficulty with pitch change is, therefore, the biggest voice symptom. In most cases the paralysis goes away on its. Own. Myasthenia gravis is a neurogenic disease in which the person experiences muscle weakness the more he or she uses those muscles. A person with MG will usually start off with a strong voice that will get weaker and weaker over a matter of minutes. SLPs can’t treat patients with myasthenia gravis, as any attempt to use the muscles necessary for speech only tire the muscles instead of strengthening them. Finally, Guillain-Barre Syndrome may or may not have an affect on voice. This disease can spread rapidly, and can require hospitalization due to total body paralysis. Speech will often be slurred and voice weak when the disease affects the larynx and oral musculature.
A patient who is diagnosed with unilateral upper motor neuron dysarthria often has a history of stroke, tumors, or other type of trauma. SLPs who work with stroke patients, in particular, should be aware that dysarthric patients may also have voice difficulties as well as swallowing difficulties. Working on increasing respiration can result in a louder voice that is less strained.
Parkinson’s Disease is a prime example of a hypokinetic dysarthria. Parkinson’s occurs because there not enough dopamine. Imprecise or slurred speech that comes out in fast rushes is characteristic of Parkinsons, and these voice and speech characteristics are often accompanied by rigidity, bradykinesia, and tremors in the person‘s body. Neurologists must diagnose and treat the patient’s medical symptoms. A team approach is typically the best; physicians should regulate medicine so that voice/speech therapy can be most effective. New technologies are becoming available to treat PD, such as deep-brain stimulation.
Hyperkinetic dysarthria occurs in several disorders which can have an affect on voice. Huntington’s disease is the most progressive and degenerative of these disorders. People with Huntington’s usually die 15-20 years post-onset. Unlike Parkinson’s disease, Huntington’s is caused by too much dopamine. This results in jerky physical movements that also manifest themselves in the voice. The SLPs job is to help facilitate communication for as long as possible. Working on voice in the early stages is important, but in later stages, AAC devices and safe eating strategies should be the focus of treatment. Note that dementia is a characteristic of Huntington’s disease. A less severe disease but one that also carries a lot of emotional weight is spasmodic dysphonia, or SD. There are two types: adductor and abductor SD. As you can imagine, the adductor type occurs when the vocal folds are tightly compressed during phonation, leaving the speaker to sound strangled as she tries to push past the laryngeal resistance. In abductor SD, the folds suddenly move away from each other, leaving the speaker in a state of aphonia. In both cases, Botox injections to relax the laryngeal musculature and behavioral voice therapy may be beneficial. Finally, essential tremor is a poorly understood neurogenic disorder that results in a shaky voice. Behavioral voice therapy is also helpful.
Mixed dysarthrias (like those found in ALS, MS, and TBI) are caused due to multiple lesion sites that affect the central and peripheral nervous systems. In later stages, concerns with dysphagia and AAC for overall communication will outweigh voice issues.
