Olfactory dysfunction and its measurement in the clinic

Abstract

The sense of smell is largely taken for granted by laypersons and medical professionals alike. Indeed, its role in determining the flavor of foods and beverages, as well as in warning of, or protecting against, environmental hazards, often goes unrecognized. This is exemplified, in part, by the fact that most patients presenting to medical clinics with "taste" problems are typically subjected to complex brain imaging and gastroenterological tests without the sense of smell even being tested or considered as a basis of the problem. Aside from frank deficiencies in sweet, sour, bitter, salty and savory (umami) sensations, "taste" disorders most commonly reflect inadequate stimulation of the olfactory receptors via the retronasal route; i.e., from volatiles passing to the receptors from the oral cavity through the nasal pharynx. This article describes the two most common procedures for measuring the sense of smell in the clinic and provides examples of the application of these tests to diseases and other disorders frequently associated with smell loss. Basic issues related to olfactory testing and evaluation are addressed. It is pointed out that smell loss, particularly in later life, can be a harbinger for not only a range of neurodegenerative diseases, but can be a prognostic indicator of early mortality.

Keywords: Allergy; Iatrogenesis; Nasal disease; Olfaction; Polyposis; Psychophysics; Rhinosinusitis; Smell.

Fig. 1

Relationship of reliability to cumulative test length for test measures amenable to such an evaluation. Best fit formulae are indicated. Modified from Doty et al. (1995). Copyright^© 1995 Oxford University Press.

Fig. 2

The University of Pennsylvania Smell Identification Test. This 40-odorant self-administered test consists of four 10-page booklets. Each page contains a different “scratch and sniff” scented strip and an associated multiple choice question. The stimuli are released using a pencil tip.

Fig. 3

The Snap and Sniff^® Threshold Test. This modern test allows for rapid and reliable determinations of detection thresholds. Concentrations of phenyl ethyl alcohol, ranging from 10⁻² to 10⁻⁹ log vol/vol in half-log concentration steps are commonly employed, along with blanks for forced-choice testing.