Flexible Endoscopic Evaluation of Swallowing with Sensory Testing

Flexible Endoscopic Evaluation of Swallowing with Sensory Testing (FEESST), is essentially a Flexible Endoscopic Evaluation of Swallowing (FEES) procedure with a formal sensory test (also known as laryngopharyngeal sensory testing) protocol included used to elicit the Laryngeal Adductor Reflex (LAR) directly using air pulses or direct touch with an endoscope.

FEES is currently used as a functional assessment of swallowing to identify and treat patients with swallowing difficulties, called "dysphagia", and to decrease their risk of aspiration (food and liquids going into the lungs instead of the stomach) and choking. FEES was invented by Speech Language Pathologist Dr. Susan Langmore, PhD in 1988, and is used primarily by Speech Language Pathologists throughout the world.

The air pulse sensory test was invented by Dr. Jonathan E. Aviv MD, FACS in 1993,^[1] and has been used by otolaryngologists (ear, nose and throat doctors),^[2] pulmonologists (lung doctors),^[3] gastroenterologists (stomach and digestion doctors),^[4] intensivists (intensive care specialists)^[5] and speech-language pathologists who perform FEES.^[6]

Swallowing consists of two distinct but interrelated processes: 1. Moving food and liquids from the mouth into the stomach through a set of coordinated muscle movements of the mouth larynx, pharynx and the esophagus 2. Protecting the airway to prevent food and liquids from entering the lungs.^[7] This natural process of swallowing can be disrupted in many ways. The problem can occur when the movements involved in swallowing are restricted due to a tumor, any type of blockage, or paralysis after a stroke. Besides the motor problems, swallowing can be impaired due to sensory dysfunction, meaning when sensation (the ability to feel) is lost or reduced anywhere in the throat area. The loss of sensation can be caused by a problem originating in the brain, such as what happens after certain types of stroke, or it can be a result of a nerve injury or swelling in the actual throat area.

The laryngeal adductor reflex (LAR), also called the glottic closure reflex, is a brainstem-mediated, involuntary reflex arc mechanism of laryngeal protection, which prevents material from inappropriately entering the upper airway. "Mechanoreceptors and chemoreceptors in the laryngopharyngeal (LP) mucosa receive innervation from the internal branch of the superior laryngeal nerve (SLN), which serves as the afferent component of the LAR. Sensory information is then transduced through the central nervous system via the nucleus tractus solitaries to the ipsilateral nucleus ambiguus in the medulla of the brainstem. The motor neurons within the nucleus ambiguus then project to the recurrent laryngeal nerve (RLN), the efferent component. In response to a unilateral stimulus, a discrete and rapid bilateral contraction of the thyroarytenoid (TA) muscles is produced"^[8]

FEES is a procedure which involves the passing of a thin flexible scope through the nose to the pharynx to assess the function of a swallow. The FEES exam protocol consists of two parts.

The first part consists of pre swallowing tasks and clinical/anatomical observations observations of the larynx and pharynx, including: volitional airway protection, movement of structures, secretion management, spontaneous swallows and obstructions. These findings inform potential impairments that may be seen during the second part of the FEES protocol.

The second part of the FEES protocol involves food, or "bolus" presentation to observe swallow function. ^[9] Food coloring is typically given in the food to track the food as it travels along the natural pink-colored tissues of the throat. The timing of the swallow and the efficiency of clearing the bolus is assessed along with the ability to protect the airway before, during and after the swallow. If the food that is given is seen to remain in the throat after the swallow it is called “residue”. Food entering the laryngeal area but not passing below the vocal folds is known as "penetration", food passing below the level of the vocal folds is known as "aspiration". The control of the bolus, or timing, relative to the onset of swallowing gestures and the sensory response is assessed to further understand why the residue, penetration, or aspiration occurred and could indicate a lack of sensation and/or motor movement problems.

The addition of a formal sensory test is optional and patient dependent, but use of a sensory test changes the Medicare billing descriptor from FEES to FEESST. The LAR is often included as part of a FEES using the "touch method" as it does not require specialized equipment beyond an endoscope. This was the only method used prior to the invention of the "air pulse" technique feature for FEESST.^[10] Clinical use of the "air pulse" method is currently lacking since this specialized equipment is no longer commercially manufactured. The "touch method" is still used during a comprehensive FEES to assess the LAR, however, studies have shown that while it can identify significant sensory deficits, inter-rater reliability may not always be high.^[11] Newer techniques are evolving that may have greater accuracy in assessing sensory responses.^[12]

When there is damage to the nerve that innervates the throat, the vagus nerve, both motor and sensory function can be affected since the vagus contains both motor and sensory nerve fibers. However, until sensory testing was developed there was no way to assess sensory loss from a vagus nerve injury. One of the most common symptoms of a vagus nerve injury is chronic cough. If a physician looked into the vocal cords of a patient with chronic cough it would appear they are opening and closing normally, however if sensory testing was performed it would give abnormal results thus indicating that the sensory nerve fibers of the vagus were somehow damaged. This would allow for a more precise diagnosis and treatment.^[13][14][15]

Another clinical situation where assessment of laryngeal sensation is helpful is in patients complaining of throat pain. Again, when examining the throat of such patients, if everything seemed to be moving well, then clinicians are often befuddled as to what the source of the throat pain is. With sensory testing, one can demonstrate that the throat tissues are numb, signifying some damage to the sensory fibers of the vagus and thereby identify vagus nerve injury as the cause of the patient's pain. This is called vagus nerve neuralgia and treatment for neuralgia can then commence.

One always sensory tests both the right and left sides of throat and the sensory levels should be symmetric, that is, the right side of the throat should normally equal the left side. However, if during sensory testing it is determined that one side is normal and the other side has a sensory deficit, then likely something has injured the vagus nerve somewhere along it lengthy course from the brain into the neck. As a result, when there is asymmetric sensory nerve loss, imaging of the neck and brain must be done to see where along the course of the vagus nerve a blockage or injury might have taken place.^[16][17]

Over the past 20 years, primarily due to work with sensory testing performed by gastroenterologists (stomach doctors) and pulmonologists (lung doctors), sensory testing and FEESST have been shown to have additional applications beyond assessing swallowing function.

For example, people with acid reflux disease, especially those with Throatburn Reflux usually have swollen vocal cords due to years of acid damage. Untreated acid-injured vocal cords will not have as sharp reflexes as vocal cords that are not swollen. Therefore, aspiration is common in people with chronic acid reflux disease. Sensory testing can quantify and assess the swelling for better treatment. The strength of the air pulse given during sensory testing in acid-injured vocal cords due to acid reflux disease will necessarily be much greater in order to elicit an airway reflex than tissues that are not swollen.^[18][19][20]