OVERVIEW

The comprehensive evaluation of the patient with dysphagia entails a detailed assessment of two distinct, but inter-related, phenomena, bolus transport and airway protection (1).

Unlike the modified barium swallow (MBS), Flexible Endoscopic Evaluation of Swallowing with Sensory Testing ( FEESST) does not involve X-ray exposure, barium administration, or the presence of a radiologist or a radiology technician. Instead, FEESST involves endoscopy, and gives direct evidence regarding the handling of secretions. Moreover, it provides an objective assessment of hypopharyngeal sensitivity which, in turn, gives the clinician information regarding a patients ability to protect their airway during the ingestion of food. Like MBS, FEESST requires the participation of a speech language pathologist (SLP), and is extremely useful in guiding the dietary and behavioral management of patients with difficulty swallowing. This paper will discuss the evolution of the endoscopic air pulse laryngopharyngeal sensory testing and its application in healthy adults, the elderly, and patients with stroke and dysphagia. A brief description of an outcome study of patients with dysphagia managed with the results of videofluoroscopy versus videoendoscopy with sensory testing will then follow. Finally, a study involving the use of laryngopharyngeal sensation to predict laryngeal penetration and aspiration will be discussed.

Kidd, et. al. have shown that assessment of pharyngeal sensation, along with severity of stroke, is related to the development of pneumonia after stroke (3). Kidd assessed pharyngeal sensation with the tip of a stick applied once to each side of the hypopharynx. Patients were asked to compare the 2 stimuli and the presence or absence of sensation was noted. Kidd was not assessing the gag reflex; he placed the stick into the hypopharynx, an area innervated by the tenth nerve. This study was one of the few in the literature which pointed out the importance of assessment of laryngopharyngeal sensory discriminative capacity as it related to development of pneumonia. However, the stick technique as described by Kidd was a crude method of sensory assessment.

One of the primary difficulties with measuring sensation in the region innervated by the superior laryngeal nerve (SLN) is that one has to directly traverse the oral cavity to arrive at the laryngopharynx. This obstacle precludes standard sensory discrimination tests such as 2-point discrimination and stereognosis (4).

Therefore, a method and technique of measuring sensory discrimination was developed which circumvented the mouth by transnasal passage of a flexible endoscope to the laryngopharynx. Through a port in the endoscope, discrete air pulse stimuli were delivered to the mucosa innervated by the SLN in order to elicit the laryngeal adductor reflex (LAR), a brainstem-mediated, fundamental sensory-motor airway protective reflex (5, 6).

I. LARYNGOPHARYNGEAL SENSORY DISCRIMINATION TESTING IN THE ELDERLY

As one ages dysphagia and aspiration during swallowing is more likely to occur (7, 8). The primary explanations for these observations have been oral and pharyngeal motor dysfunctions such as abnormal lingual activity, poor lingual-palatal seal and pharyngeal pooling (7, 9). However, it has been shown that oral cavity sensory discriminatory ability diminishes with advancing age (10, 11). The possibility that laryngopharyngeal sensory capacity also diminishes with age had not been studied.

To address this issue, endoscopic air pulse stimulation of the SLN mucosa was conducted in 56 healthy adults ranging in age from 23-87 with a mean of 47 + 20 years. In general, there was a progressive increase in sensory discrimination threshold with each decade of life. A correlation analysis revealed that there were significant increases in pressure thresholds with advancing age (r = 0.62, p < 0.001). For subjects 20-40, average threshold was 2.07 + 0.20 mm Hg air pulse pressure (APP); for the 41-60 age group, 2.22 + 0.34 mm Hg APP and for subjects 61 and older, 2.68 + 0.63 mm Hg APP. Thresholds for the 61 and older group were significantly different from those for the 20-40 and the 41-60 groups (p < 0.05) (12).
One of the most interesting studies to suggest that sensory deficits might play a key role in the development of dysphagia and aspiration in the elderly came from a landmark study of cadaveric SLN's (13). The ultrastructural changes that took place with increasing age in the human SLN were examined and an extensive and statistically significant decrease in the number of sensory nerve fibers in subjects over 60 years of age were found (13). Our observations represented a striking clinical correlate to these histomorphologic findings.

II. LARYNGOPHARYNGEAL SENSORY DISCRIMINATION TESTING IN STROKE PATIENTS WITH DYSPHAGIA

Subsequent to the study of age related changes in sensation, a study of laryngopharyngeal sensation in stroke patients with dysphagia was carried out. This was a prospective study evaluating sensory capacity of the laryngopharynx in supratentorial or brainstem stroke patients who presented with dysphagia (14). Fifteen stroke patients (mean age 66.7 + 13.8 years) were prospectively evaluated using the endoscopic air pulse technique. There were 15 age-matched controls. No sensory deficits were found in any of the age matched controls. In all stroke patients studied, either unilateral (n = 9) or bilateral (n = 6) sensory deficits were identified. Deficits were defined as either a moderate impairment in sensory discrimination thresholds (4.0 - 6.0 mm Hg APP) or a severe sensory impairment (> 6.0 mm Hg APP). These elevations in sensory discrimination thresholds were significantly greater than age-matched controls (7.05 + 0.17 mm Hg APP for the supratentorial stroke group, 6.05 + 1.22 mm Hg APP for the infratentorial stroke group vs. 2.61 + 0.69 mm Hg APP for the controls). Among patients with unilateral deficits, sensory thresholds were moderately to severely elevated in all 9 cases on the affected side compared with the unaffected side (p < 0.01, Fisher's exact test). Moreover, the sensory thresholds of the unaffected side were not significantly different from those of age matched controls (2.51 + 0.25 mm Hg APP vs. 2.61 + 0.69 mm Hg APP, respectively, p > 0.05).

As described in the introductory paragraph, combining endoscopic evaluation of swallowing (15, 16) with endoscopic air-pulse sensory discrimination testing results in FEESST. FEESST was prospectively performed 148 times in 133 patients with dysphagia over an 8-month period (2). The patients had a variety of underlying diagnoses, with stroke and chronic neurological disease predominating (n=94). Treatment was based on results of the FEESST, and consisted of dietary modifications (upgrade/downgrade), behavioral modifications and gastrostomy tube placement. All patients successfully completed the examination. In 111 (75%) of the evaluations, unilateral or bilateral severe sensory deficits were found. 47% of evaluations with severe deficits compared to 11% of evaluations with either normal sensitivity or moderate sensory deficits displayed aspiration (p < .001, chi-squared test with one degree of freedom). 69% of evaluations with severe deficits compared to 24% with normal or moderate deficits displayed laryngeal penetration (p < .001, chi-squared test with one degree of freedom) (2). This study suggested an association between sensory deficits and the development of laryngeal penetration or aspiration on any given swallow.


III. OUTCOMES: FEESST VS. Modified Barium Swallow (MBS)

A randomized, prospective cohort outcome study in a hospital-based outpatient setting was performed in order to investigate whether FEESST or MBS was superior as the diagnostic test for evaluating and guiding the behavioral and dietary management of out-patients with dysphagia (17). One hundred and twenty six outpatients with dysphagia were randomized to either FEESST or MBS as the diagnostic test used to guide dietary management and behavioral management (postural changes, small bites and sips, throat clearing). The outcome variables were pneumonia incidence and pneumonia-free interval. The patients were enrolled for one year and followed for one year.

Seventy-eight MBS examinations were performed in 76 patients with 14 patients (18.4%) developing pneumonia; 61 FEESST examinations were performed in 50 patients with 6 patients (12.0%) developing pneumonia. These differences were not statistically significant (c2 = 0.93, p = .33). In the MBS group, the median pneumonia-free interval was 47 days; in the FEESST group, the median pneumonia-free interval was 39 days. Based on a Wilcoxon signed-rank test, this difference was not statistically significant (z = 0.04, p = 0.96).

In specifically examining the patients who had an underlying diagnosis of stroke, the following was noted: in the MBS group 7/24 patients developed pneumonia (29.2%) while in the FEESST group 1/21 (4.76%) developed pneumonia. This difference was statistically significant (p =0.05, Fisher's exact test).

There are two possible reasons dietary and behavioral management of stroke patients guided by FEESST resulted in better outcomes than those seen in patients whose management was guided by MBS. One reason is related to the greater amount of time that is allowed for a FEESST relative to a MBS, so that patient fatigue and its sequellae are more readily identified and managed. Patients with stroke have been shown to experience fatigue of the pharyngeal phase of swallowing as they progress through a meal (18, 19). The other reason for the marked difference in stroke patient outcomes may be related to the fact that information regarding the sensory or afferent component of the swallow is rigorously assayed with FEESST while only indirectly addressed with MBS. As a result, the clinician using FEESST has a heightened awareness of potential aspiration and pneumonia risks that might otherwise have been overlooked.

In conclusion, whether dysphagic out patients have their dietary and behavioral management guided by the results of MBS or FEESST, their outcomes with respect to pneumonia incidence and pneumonia-free interval are essentially the same.

IV. LARYNGEAL ADDUCTOR REFLEX and PHARYNGEAL SQUEEZE AS PREDICTORS OF LARYNGEAL PENETRATION and ASPIRATION

The contribution of laryngopharyngeal (LP) sensory deficits to the outcome of a swallow has been unclear, also, the relationship between sensory and motor deficits in the laryngopharynx has also been unclear. The purpose of this study was to determine if patients with LP sensory and motor deficits were at increased risk for laryngeal penetration and aspiration during swallowing and to determine the relationship between pharyngeal motor weakness and LP sensory deficits. Endoscopic evaluation of swallowing with sensory testing was performed on 122 patients with dysphagia who were prospectively divided into 2 groups. The control group was 76 patients with normal sensitivity- determined by an intact laryngeal adductor reflex (LAR) upon air pulse stimulation of the mucosa innervated by the superior laryngeal nerve. The study group was 46 patients with severe sensory deficits - determined by an absent LAR. Each group was given puree followed by thin liquid noting presence or absence of laryngeal penetration and aspiration. Pharyngeal muscle strength was assessed by noting presence or absence of pharyngeal contraction during voluntary adduction of the vocal folds (pharyngeal squeeze).
In the control group, with purees, 6/76 (7.90%) penetrated, 3/76 (3.94%) aspirated; with thins, 26/76 (34.2%) penetrated, 13/76 (17.1%) aspirated. In the absent LAR group, with purees, 39/46 (84.8%) penetrated, 32/46 (69.6%) aspirated; with thins, 46/46 (100%) penetrated, 43/46 (93.5%) aspirated. For both consistencies, the differences in prevalence of penetration and aspiration between groups was significant (p<0.0001, c2).

In controls, pharyngeal squeeze was impaired in 17/76 (22.4%), with penetration of puree in 6/17 (35.3%) and aspiration in 3/17 (17.6%). In the absent LAR group, squeeze was impaired in 41/46 (89.1%), with penetration of puree in 39/41 (95.1%) and aspiration in 32/41 (78.0%). The difference in the prevalence of pharyngeal weakness between groups was significant (p<0.0001). The difference in the prevalence of penetration and aspiration was higher in the absent LAR/ impaired contraction cohort than in the normal sensation/impaired contraction cohort (p<0.0001). We conclude that absence of the LAR and impaired pharyngeal squeeze puts patients with dysphagia at high risk for laryngeal penetration and aspiration compared to patients with an intact LAR and intact pharyngeal squeeze. There is a strong association between motor and sensory deficits in the laryngopharynx (20).

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