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Understanding Vocal Fold Paresis/Paralysis
What are vocal fold paresis and paralysis?
Vocal fold paresis and paralysis comprise a continuum of abnormal nerve inputs to the voice box muscles
(laryngeal muscles) – ranging from the loss of some to all neural input.
- Paralysis is due to the total interruption of nerve impulse resulting in no movement of the muscle.
- Paresis is the partial interruption of nerve impulse resulting in weak or abnormal motion of laryngeal muscle(s).
Vocal Fold Paralysis Versus Normal Vocal Folds – Open Position
| One-Sided Vocal Fold Paralysis |
Normal Vocal Folds |
Paralyzed
left vocal fold (*vf) is foreshortened and appears "fatter" due to loss
of muscle tone; the surrounding areas (indicated by yellow arrows) are
also affected and seem to "collapse" onto the vocal folds in contrast
to normal vocal folds.
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Normal vocal folds on inspiration (open); note right and left vocal folds open equally from the imaginary midline [-----].
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(click photos for larger images) |
 Key Information Viewed with patient facing examiner: vf, vocal folds; R, right side of patient; L, left side of patient
What nerves are involved in vocal fold paresis/paralysis?
Like all other voluntary movements of the body, vocal fold movements
are a result of the coordinated contraction of various muscles. These
muscles are controlled by the brain through a specific set of nerves.
Brain signals responsible for movement (motor signals) intended for the voice box travel through the tenth cranial nerve or vagus nerve.
Each side of the voice box receives its own set of signals from the brain through two named nerves.
- Superior laryngeal nerve (SLN): Carries
signals to the voice box muscle that is between the cricoid and thyroid
cartilages of the voice box, hence the name, cricothyroid muscle. (For more information, see Anatomy & Physiology of Voice Production.)
Since
the cricothyroid muscle is involved in adjusting the tension of the
vocal fold for high notes during singing, SLN paresis and paralysis
result in:
- Abnormalities in how high or low the voice is (pitch)
- Inability to sing with smooth change to each higher note (glissando or pitch glide)
Because the other voice box muscles are still active, the vocal
folds may still appear to move normally. This may make the diagnosis of
SLN paresis/paralysis difficult in some cases. Sometimes, patients with
SLN paresis/paralysis may have a normal speaking voice but an abnormal
singing voice.
- Recurrent laryngeal nerve (RLN): Carries signals to different voice box muscles responsible for:
- opening vocal folds (as in breathing, coughing)
- closing vocal folds for vocal fold vibration during voice use
- closing vocal folds during swallowing
(For more information, see Anatomy & Physiology of Voice Production.)
Basis of Name
The recurrent laryngeal nerve or RLN is called such because its path
"recurs," i.e., goes into the chest cavity and curves back into the
neck until it reaches the larynx.
Long Course = Increased Risk for Injury
Because the RLN is relatively long and takes a "detour" to the voice
box, the RLN has greater risk of injury from quite different causes –
such as infections and tumors of the brain, neck, chest, or voice box;
as well as complications during surgical procedures in the head, neck,
or chest regions – that directly injure, stretch, or compress the nerve.
Increased Risk for Injury = Majority of Cases
Consistent with its longer course and corresponding higher risk for
injury, the recurrent laryngeal nerve is involved in majority of cases
of vocal fold paresis or paralysis.
What are the causes of vocal paralysis/paresis?
| Cause |
Effects on Laryngeal Nerves
RLN: Recurrent Laryngeal Nerve
SLN: Superior Laryngeal Nerve |
Inadvertent injury during surgery |
Because
of the length of the RLN, surgery in the neck (e.g., surgery of thyroid
gland, carotid artery) or surgery in the chest (e.g., surgery of the
lung, esophagus, heart, or large blood vessels) may inadvertently
result in RLN paresis or paralysis. The SLN may also be injured during
head and neck surgery. |
Complication from endotracheal intubation |
Very
rarely, injury to the RLN may occur when breathing tubes are used for
general anesthesia and/or assisted breathing (artificial ventilation).
However, this type of injury is rare, given the large number of
operations done under general anesthesia. |
Blunt neck or chest trauma |
Any type of penetrating, hard impact on the neck or chest region may injure the RLN; impact to the neck may injure the SLN. |
Tumors of the skull base, neck, and chest |
Tumors
(both cancerous and non-cancerous) can grow around nerves and squeeze
them (compression), resulting in varying degrees of paresis or
paralysis. |
Viral infections |
Inflammation
from viral infections may directly involve and injure the vagus nerve
or its nerve branches to the voice box (RLN and SLN). |
Other causes |
Systemic illnesses affecting nerves in the body may also affect the nerves to the voice box |
Unknown cause or idiopathic |
Despite
advances in diagnostic technology, physicians are unable to detect the
cause in about half of all vocal fold paralyses. These cases are
referred to as idiopathic (due to unknown origins). In idiopathic
cases, paralysis or paresis might be due to a viral infection affecting
the voice box nerves (RLN or SLN) or the vagus nerve, but this cannot
be proven in most cases. |
Key Information
- Knowing
the cause of vocal fold paralysis or paresis can provide clues as to
whether the disorder will resolve over time or whether it is most
likely permanent.
- When a reversible cause is present,
surgical treatment will most likely not be recommended given the
likelihood of spontaneous resolution of the paresis or paralysis.
Who does vocal fold paresis/paralysis affect?
Anyone – No Particular Age or Gender Susceptibility
Vocal fold paresis/paralysis can happen at any age – from newborns
to the very old, males and females alike, from a variety of causes.
Impact Varies According to Person's Voice Demands
The effect on patients may vary greatly depending on the voice
demands of the patient. For example, mild vocal fold paresis can be
"devastating" to a singer's career, but have only a minimal effect on a
computer programmer's career.
Case-to-Case Differences
Even if the cause is the same, every case of vocal paresis/paralysis is always slightly unique because:
- Degrees of weakness of the voice box muscles vary
- Adaptation of other laryngeal muscles adapt varies
- Patient needs vary and are affected by gender, age, as well as overall health.
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