Diagnosis of Vocal Fold Paresis/Paralysis

Key Glossary Terms

Paresis
Partial paralysis; partial loss of nerve input to a muscle, resulting in muscle weakness

Paralysis
Complete loss of nerve input to a muscle resulting in complete loss of muscle function

Laryngeal Electromyography (LEMG)
Test that measures electrical signals of nerve inputs to muscles

Recurrent Laryngeal Nerve (RLN)
Branch of vagus nerve to voice box muscles that open and close vocal folds

Superior Laryngeal Nerve (SLN)
Branch of vagus nerve to cricothyroid muscle involved in control of pitch

Glossary

It is important to identify vocal fold paresis/paralysis and identify its cause(s).

A complete evaluation of a voice disorder caused by vocal fold paresis or paralysis needs to address the questions below.

1. Is vocal fold paralysis/paresis present?
2. Is the vocal fold paralysis/paresis one-sided (unilateral) or two-sided (bilateral) – i.e., are one or both vocal folds affected?
3. Which voice box muscle(s)/nerve(s) are affected?
4. What is the cause(s) of your vocal fold paralysis/paresis?
5. What is the likely outcome (prognosis) of the vocal fold paralysis/paresis – spontaneous recovery? permanent loss of motion? worsening?

The examination of the voice box (laryngeal examination) by the laryngologist can provide important clues in determining whether vocal fold paresis or paralysis is present. During the examination, multiple aspects can be assessed such as vocal fold motion, strength, position, tension, mass, and overall voice function. (For more information, see Overview of Diagnosis, Treatment & Prevention.)

Key Information

Immobility as Hallmark of Paralysis

Immobile vocal fold is the hallmark of vocal fold paralysis; reduced speed of motion and/or reduced range of motion are often found in vocal fold paresis. Vocal motion is usually evaluated while the patient is breathing, sniffing, and making sound (voice production).

Vocal Fold Immobility Not Equal to Vocal Fold Paralysis

• These terms are not identical because a number of non-nerve related conditions (such as joint arthritis, subglottic stenosis, or vocal fold trauma) can also cause vocal fold immobility.
• These other causes need to be considered in the workup of the voice disorder.

Paralysis Purely a Nerve-Related Problem

The term "vocal fold paralysis" should only be used when a nerve-related problem causes the loss of normal vocal fold motion.

Consideration of Systematic Illnesses

Occasionally, degenerative or acute neurologic disorders such as Parkinson's disease, multiple sclerosis, and brain stem strokes can result in a voice disorder alone or before affecting the rest of the body. In these conditions, the paresis/paralysis is present but is part of a larger neurological disorder. A joint evaluation with a neurolaryngologist and a neurologist may be necessary to evaluate the myriad causes in this category.

The examination of the voice box provides sufficient information to assess whether one or both vocal folds is/are abnormal. Determining whether one or both vocal folds are affected is important in the treatment plan.

Voice box muscles are named according to the cartilages to which they are attached.

Identification and assessment of outcome: Depending on the suspected cause, a variety of tests may be ordered. One of the more important tests is laryngeal electromyography (LEMG). (For more information, see LEMG.)

LEMG measures electrical currents in the voice box muscles that are the result of nerve inputs. Measuring and looking at the pattern of the electric currents provides key clues about:

• Whether the voice box muscle is paralyzed or paretic
• Whether there is some hint of recovery or repair of nerve inputs (re-innervation)
• The degree of the nerve input problem.

LEMG involves the insertion of small needles that can measure electrical currents in the vocal fold muscles. During LEMG patients perform a number of tasks that would normally elicit characteristic actions in the tested muscles.

Paralysis and paresis have their typical "signatures" of electric current pattern. Certain electrical signatures from muscle are quite characteristic of nerve injury and repair. These electrical patterns give the clinician insight as to the timing, duration, and severity of the nerve injury.

Note: In some cases of arthritis or laryngeal joint problems, the nerve activity is normal. This will point the diagnosis away from that of paresis and paralysis.

In many cases, LEMG is a useful indicator in determining outcome (prognosis) of a patient's condition.

Key Information

Subtle Clues
Vocal fold paresis results in a decrease of vocal fold movement, as well as voice weakness and low tone. These findings and the patient complaints associated with them are milder and more subtle in vocal fold paresis than in paralysis.

LEMG Role in Identification
Vocal fold paresis is not easily recognized because vocal fold motion is still present. Identification of vocal fold paresis may require LEMG studies which can detect abnormalities in electrical signals of muscles (electromyographic abnormalities) in the presence of seemingly normal vocal fold motion.

Determining whether vocal fold paresis/paralysis is one-sided or two-sided directs where to look for the probable cause. Likewise, knowing which muscles are affected also provides clues as to which nerve, whether RLN or SLN or both, is affected. Knowing which nerve is affected also directs where to look for the probable cause.

The presence of a systemic illness provides clues as to possible causes as well as guidelines for treatment plans.

Because there is a wide list of diseases that may cause a nerve to be injured, further testing is usually necessary (blood tests, x-rays, CT scans, MRI, etc.) to identify the cause(s) of vocal fold paresis/paralysis.

For example, a neurological consultation may be requested to see if there are nerves other than those to the voice box (RLN and/or SLN) affected. According to current best practices, a CT scan of the skull base to the chest may be ordered to check for masses that may be pushing on the nerve as it travels to the larynx from the base of the brain. Laboratory tests such as screening for diabetes, thyroid disease, and infectious and immune disorders may be ordered to make sure the laryngeal paralysis is not part of a more systemic disorder. (For more information, see How Breakdowns Result in Voice Disorders and Voice Dysfunction in Neurological Disorders.)

Red Flag

Need to Pursue Diagnosis

Persistent hoarseness or voice symptoms should not be left without diagnosis.

Voice Center Consultation

When the cause of persistent hoarseness remains a problem, referral to a voice center where more extensive testing can be done is the best course of action. These cases are often diagnosed as vocal fold paresis by Voice Centers. In some cases of vocal fold paresis, the differences in vocal fold motion impairment may be quite subtle and must be brought out by repetitive testing.

Masking of Vocal Fold Paresis

A more prominent diagnosis can mask the diagnosis of vocal fold paresis. Vocal fold paresis, when present with functional muscle tension dysphonia, is usually overlooked.

Even if the physician has determined that the vocal fold immobility is due to nerve paralysis, determining the underlying cause of vocal fold paralysis is important.

For example, vocal fold paralysis may be due to cancer compressing or involving the nerve. The paralysis could be the first symptomatic manifestation of the tumor. Thus it is crucial for the physician to carefully look along the paths of the vagus and recurrent laryngeal nerve for a cancer that could be invading the nerve and causing the vocal fold paralysis. Cancers that commonly cause a vocal fold paralysis are cancers of the lung, esophagus, and thyroid gland. Thoracic malignancies (cancerous tumors growing in the chest) that grow on top of nerves in the chest are also one of the more common causes of paralysis. Clearly, early diagnosis of cancer would impact the overall treatment course.

Most vocal fold paralyses are not caused by cancer. However, the importance of making a diagnosis of cancer promptly, if cancer is the cause of vocal fold paralysis, is so important that current best practices suggest that every patient who develops vocal fold paralysis should be evaluated for possible nerve compression by tumor.

Red Flag

Identification of Vocal Fold Paresis Is Frequently Missed

Since its patient complaints with paresis can be mild and hardly noticeable, as well as so similar to those of other voice disorders, the disorder can be easily misdiagnosed.

Hard-to-Find Clues

Often, the only physical sign of paresis present is a slight asymmetry in the opening and closing motions of the vocal folds, or a slight variation in the tension of the two folds. These findings can be subtle and can be easily missed on examination of the voice box.

Importance of Careful Voice Box Examination

The importance of a careful and detailed throat and voice box examination cannot be overestimated.

Role of LEMG

Testing by LEMG plays a major role in definite identification of vocal fold paresis.

Red Flag

Any and all airway problems require immediate attention.