Measurement of chemosensory function

Abstract

Although hundreds of thousands of patients seek medical help annually for disorders of taste and smell, relatively few medical practitioners quantitatively test their patients' chemosensory function, taking their complaints at face value. This is clearly not the approach paid to patients complaining of visual, hearing, or balance problems. Accurate chemosensory testing is essential to establish the nature, degree, and veracity of a patient's complaint, as well as to aid in counseling and in monitoring the effectiveness of treatment strategies and decisions. In many cases, patients perseverate on chemosensory loss that objective assessment demonstrates has resolved. In other cases, patients are malingering. Olfactory testing is critical for not only establishing the validity and degree of the chemosensory dysfunction, but for helping patients place their dysfunction into perspective relative to the function of their peer group. It is well established, for example, that olfactory dysfunction is the rule, rather than the exception, in members of the older population. Moreover, it is now apparent that such dysfunction can be an early sign of neurodegenerative diseases such as Alzheimer's and Parkinson's. Importantly, older anosmics are three times more likely to die over the course of an ensuring five-year period than their normosmic peers, a situation that may be averted in some cases by appropriate nutritional and safety counseling. This review provides the clinician, as well as the academic and industrial researcher, with an overview of the available means for accurately assessing smell and taste function, including up-to-date information and normative data for advances in this field.

Keywords: Age; Ageusia; Anosmia; Detection; Hypogeusia; Hyposmia; Identification; Olfaction; Psychophysics; Smell; Taste; Threshold.

Fig. 1

The Snap & Sniff^® threshold test. The test kit is comprised of 20 smell “wands”. Five contain no odor and the others contain, in the case of the standard odorant phenyl ethyl alcohol, half-log stimulus dilutions ranging from 10⁻² (strongest) to 10⁻⁹ (weakest) concentrations. When the thumb of the operator pushes the black ring forward, an odorized tip is presented to the subject. Releasing the ring retracts the tip back into the wand's housing. This test makes it impossible to touch the nose to the odor source. Photographs courtesy of Sensonics International, Haddon Heights, New Jersey USA. Copyright © 2017, Sensonics International.

Fig. 2

The self-administered computerized olfactory test system (SCOTS). The dome, which can be readily exchanged for other domes with different sets of odors, contains up to 40 odorants that can be individually released, or released in combination, to the sniffing port. The standard configuration in a single dome is a 12-item smell identification test and a phenyl ethyl alcohol threshold test analogous to the one employed in the Snap & Sniff^® threshold test (Fig. 1). Photograph courtesy of Sensonics International, Haddon Heights, New Jersey USA. Copyright © 2017, Sensonics International.

Fig. 3

Frequency distribution of Snap & Sniff^® bilateral detection threshold test scores. n = 386. Odorant is phenyl ethyl alcohol (PEA). Scores ≥-2.00 are indicative of total anosmia. Copyright © 2017 Sensonics International, Haddon Heights, NJ USA.

Fig. 4

The 40-odor University of Pennsylvania Smell Identification Test (UPSIT). This test is comprised of four booklets, each containing 10 microencapsulated (“scratch and sniff”) odors which are released by a pencil tip. The examinee is required to provide an answer on each test item (see columns on last page of each booklet) even if no odor is perceived or the perceived odor does not smell like one of the response alternatives (i.e., the test is forced-choice). Photograph courtesy of Sensonics International, Haddon Heights, New Jersey USA. Copyright ©2017, Sensonics International.

Fig. 5

Male normative data for the University of Pennsylvania Smell Identification Test (UPSIT; n = 1819). Female normative data are found elsewhere (Doty¹¹). Note classification of dysfunction in absolute terms (normosmia, mild microsmia, moderate microsmia, severe microsmia, anosmia), as well as relative terms (percentiles for age categories). Note also that low test scores suggest avoidance of correct responses in a forced-choice situation, i.e., probable malingering. From Doty. Copyright ©2017, Sensonics International.

Fig. 6

Examples of four types of rating scales. From left to right: (a) a labeled magnitude scale; (b) standard category scale in which the subject provides answers in discrete categories; (c) a visual analogue or graphic scale with anchors (descriptors) at each end; (d) a category scale with logarithmic visual density referents to denote non-linear increasing magnitudes of sensation, with verbal anchors at each end. Copyright © 2002, Richard L. Doty.

Fig. 7

Magnitude estimates given to six concentrations of amyl butyrate after adjustment for number usage by using a cross-modal matching procedure. Each age group was comprised of 10 men and 10 women, the younger ranging from 18 to 26 years and older ranging from 65 to 85 years. From Stevens and Cain, with permission. Copyright © 1982, ANKHO International, Inc.

Fig. 8

Left: A modern electrogustometer and its electrodes. This device can apply a wide range of perithreshold currents with the electrode on the tongue being either the anode (standard confirmation) or cathode. Right: A modern clinical taste testing system employing plastic disposable tabs whose ends are embedded with tastants. Photograph courtesy of Sensonics International, Haddon Heights, New Jersey USA. Copyright © 2017 Sensonics International.

Fig. 9

Mean NaCl detection thresholds (±SEM) on the anterior tongue as a function of stimulus duration plotted on log–log axes. The four data points, from left to right, correspond to 200, 400, 750 and 1500 ms. The relationship between threshold and stimulus duration represents a power function. From Bagla et al. Copyright © 1997 Oxford University Press.

Fig. 10

Left: University of Pennsylvania Regional Automated Taste Testing System (RATTS). From: Bagla et al, Copyright © 2001 Elsevier Science, Inc. Right: Glass stimulation device viewed from below. The stimuli flow through the 25 mm central chamber (A). A vacuum is present on the annular chamber (B) which holds the device securely to the tongue. The pressure (∼40 mmHg) was calibrated with a differential pressure gauge connected by a tube to the distal end of the vacuum chamber (C). Copyright© 1997 Oxford University Press.

Fig. 11

Left: Mean (±SEM) threshold values obtained from 8 subjects for NaCl presented to the four anterior tongue regions for two stimulation areas (12.5 and 50 mm²). The number of papillae counted under videomicroscopy is indicated by the dark bars, and threshold values by the gray bars. Note that the threshold scale is inverted, such that greater sensitivity is depicted at the top of the scale. Right: Tongue regions where stimulators were centered. From Doty et al. Copyright © 2001 Elsevier Science Inc.

Fig. 12

Mean (±S.E.M.) number of fungiform papillae and current density thresholds on four anterior tongue sites for two different sized electrode areas. From Doty et al. See Fig. 11 for depicted stimulation sites. Copyright © 2001 Elsevier Science Inc.

Fig. 13

Influence of Terbinafine (Lamisil^®) on taste identification test scores for stimuli representing the four major taste qualities. The agents were presented to left and right anterior and posterior regions of the tongue using micropipettes. The test scores represent the summation of scores across all four lingual regions. Dark bars are terbinafine patients and gray bars controls (see text for details). From Doty & Haxel. Copyright © 2005 The American Larygological, Rhinological and Otological Society, Inc.

Fig. 14

Mean (±SEM) percent correct performance of 29 PD patients and 29 matched controls in identifying the bitter taste quality of caffeine at each of five stimulus concentrations. From Doty et al. Copyright © 2015 Springer.

Fig. 15

Mean (±SEM) whole mouth taste intensity ratings for five concentrations of NaCl (salty) in anosmics, hyposmics and normosmics. P values are for olfactory function group main effects from ANOVAs performed on data from each stimulus concentration. This shows no effect of smell impairment on intensity rating to NaCl. From Stinton et al. Copyright © 2010 American Psychological Association.

Fig. 16

Perceived taste intensity as a function of fungiform papillae density on the anterior tongue. Graphs on the left were obtained with the gLMS; graphs on the right were obtained with a nine-point category scale. All correlations between the papilla density and perceived intensity on the left were statistically significant (P < 0.05), but only the correlation for quinine was significant on the right. From Snyder et al. Copyright © 2004 Imprint Academic.

Fig. 17

Perceived magnitude of electrical taste (converted to a tone level) as a function of electrical stimulus intensity in dB using an electrogustometer. n = 12. From Salata et al. Copyright © 1991 Oxford University Press.