General Medical Information

Olfactory Function And Dysfunction

Richard L. Doty
Daniel A. Deems

The sense of smell serves as a sentinel for assessing the quality of the air entering the respiratory system, alerting the individual of environmental pollutants, smoke, and numerous toxic agents. Such a function is of considerable consequence, as the average adult breathes in approximately 15 kg of air each day, in contrast to taking in only approximately 1.5 kg of food and 2 kg of water, and even small amounts of pollutants can pose a significant burden on the respiratory tract. Warning agents added to natural gas by public works companies capitalize on the extreme sensitivity of this sensory system to airborne chemicals, and olfaction is the first sensory system to detect volatiles arising from spoiled foods and beverages. Aside from aiding in the avoidance of dangerous environments and foodstuffs, this primary sensory modality plays a significant role in mediating a wide range of aesthetic pleasures and largely determines the flavor of foods and beverages. Indeed, most patients presenting with complaints of decreased taste function have, in fact, loss of olfactory function, reflecting decreased effectiveness of retronasal stimulation of the receptors by flavor molecules arising from food during deglutition.

Olfactory loss or distortion is of considerable personal and practical significance to the patient, particularly ones whose lifestyle, livelihood, or immediate safety depends on a normal sense of smell (e.g., cooks, firemen, homemakers, plumbers, professional food and beverage tasters, employees of natural gas works, chemists, and numerous industrial workers). Importantly, subtle alterations in smell function, often detectable only by quantitative testing, can be an early sign of such neurological disorders as Alzheimer disease (AD) and idiopathic Parkinson disease (PD)—disorders where early pharmacologic intervention can be critical. Unfortunately, some patients are notoriously inaccurate in describing the current state of their chemosensory function. Hence, it behooves the otolaryngologist to be familiar with modern means for accurately and objectively assessing olfactory function in the office setting, including means for detecting malingering. Many patients who believe they have a smell problem do not upon objective testing, whereas others are unaware of a clear deficit.

The goal of this chapter is to provide the otolaryngologist with a basic understanding of the anatomy and physiology of the olfactory system, practical ways to accurately and quantitatively assess its function, and a guide for identifying and managing patients with common olfactory disorders.