Smell and Taste Disorders—Diagnostic and Clinical Work-Up

10.1055/b-0034-91132

Smell and Taste Disorders—Diagnostic and Clinical Work-Up

Antje Welge-Luessen, Donald A. Leopold, Takaki Miwa

Introduction

Smell and taste disorders are common complaints presenting to ear, nose, and throat (ENT) physicians.1–3 Approximately one-fifth of all adults have some form of olfactory dysfunction,2,4,5 increasing to 30% or more suffering from functional anosmia over the age of 70 years.2 These numbers are reflected by 79,000 patients/year in central Europe (Austria, Germany, and Switzerland),6 and around 200,000 patients/year in the USA,7 consulting ENT specialists about olfactory disorders.

Taste disorders seem to be less common, affecting around 5% of people8 if diagnosed by two different psychophysical tests. If, however, only four tastants are applied and the incorrect identification of one of these four is defined as taste disorder, then the prevalence rises to almost 20%.5 Other epidemiological studies, using questionnaires to evaluate the number of self-perceived taste disorders, report numbers in the range of 0.6%7 to 0.93%.9 These numbers increase to 8.7% in patients seeking medical advice.3 The fact that there are three different nerves on each side, all transmitting taste information, makes this sense more robust than the sense of smell, and less likely to decrease through life.

Even though olfactory receptor cells regenerate throughout life, this regeneration seems to decrease with growing age. Patients suffering from age-related olfactory dysfunction are often not even aware of the disorder,10 which usually develops gradually and is most likely due to the reduced regenerative capacity of the olfactory receptor cell. In contrast to hearing and visual losses, which are often noticed by spouses, family members, or friends, smell losses usually remain undetected by other persons. This might explain why patients with olfactory disorders, particularly older people, are more likely to encounter hazardous events (e.g., burning food, ingesting spoiled food, fire) than a normosmic control group.11,12 These hazards have to be especially mentioned when counseling patients with smell loss. The increased risk of these hazards contributes to the loss in quality of life experienced by patients suffering from smell loss. Both the increased risk of hazardous events and the reduction in quality of life are likely to explain why patients with post-traumatic smell loss receive some financial reimbursement from insurance providers (see Chapter 18). With growing age, the sense of taste also decreases, but less than the decline seen in olfaction.9,13,14

Making an accurate diagnosis of smell or taste disorder is essential in order to determine appropriate treatment and counseling. The first step is to determine whether the disorder is an olfactory problem, a gustatory problem, or both. As patients do often complain about taste problems or complain simply that, “the food just does not taste the same anymore,” it is first necessary to evaluate the kind of chemosensory deficit present.

It has been established for some years now that self-assessment of olfactory function is unreliable.15 Even in patients complaining of olfactory disorders, self-assessment correlates only moderately with measured olfactory function.16,17 The use of a validated test that actually measures olfactory ability, gustatory ability, or both is therefore mandatory in all patients seeking advice (see Chapter 6 for smell testing; Chapter 14 for taste testing).

Olfactory Disorders

The vast majority of chemosensory complaints are olfactory, and the patient′s history can help to classify the disorder. Smell disorders are classified as sinonasal, postinfectious, post-traumatic, congenital, toxic (including drug-induced disorders), other (postoperative), and idiopathic. The detailed characteristics of each of these disorders are discussed in the following chapters; however, in clinical consultations it is important to differentiate between sinonasal (sometimes called “conductive”) and nonsinonasal (sometimes called “neural”) disorders within the initial work-up.

Assessment of a patient depends on the situation. In general, one has to distinguish between an asymptomatic patient who has to be evaluated because of a medicolegal reason (e.g., preoperatively [before any endonasal operation] or in the context of a thorough ENT examination [e.g., for an expert opinion]) and a patient presenting with an olfactory complaint. In asymptomatic patients, the use of a validated screening test is recommended (see Chapter 6). It is important to bear in mind that the test has been adapted to cultural factors18,19 (for details, see Chapter 6). Only if this test reveals any pathological results is further testing required. In Japan, a self-administered odor questionnaire is sometimes used as an instant index.17

However, patients seeking medical advice for olfactory disorders have different expectations. They expect not only a diagnosis, but also information concerning prognosis and treatment (or, at least, coping strategies in cases in which therapeutic tools are lacking). To meet these expectations, classification of the disorder is mandatory.

Gustatory Disorders

Like olfactory disorders, gustatory disorders should be classified and measured using a validated test. Unlike preoperative smell testing before endonasal operations, there is currently no consensus about the need for preoperative taste testing in asymptomatic patients undergoing enoral operations such as tonsillectomy or teeth extraction. Whether this approach will change in the future remains to be seen, and is likely to depend on the number of complaints about postoperative taste problems observed in such patients (for details, see Chapter 15).

Nevertheless we do recommend performing a screening taste test in every patient receiving an extensive olfactory test, and vice versa.

Examination of the Patient

History: Olfaction

The importance of a detailed history cannot be overemphasized. Of special importance is the time course of the complaint.

Has the disorder started suddenly or has it developed over a longer period of time? In this context, it is important to remember that the patient should recall a temporal connection to, for example, accidents, intake of medication, or acute infection such as rhinitis or rhinosinusitis. However, the examiner should be cautious not to overinterpret possible causative correlations sometimes offered by patients.

Has the patient ever experienced something like this before? Are there any additional nasal symptoms (discharge, rhinorrhea, postnasal drip, nasal breathing) or concomitant diseases (e.g., thyroid, cardiopulmonary, hepatic, or renal disease, or allergies)? A history of movement disorders (tremor, etc.) or disturbances in memory should also be taken. A family history of Parkinson or Alzheimer disease should be evaluated and considered.

The existence of additional qualitative disturbances, if not mentioned spontaneously, should also be evaluated (see below). The use of a simple history questionnaire as depicted in Fig. 5.1 (adapted from ref. 20) can be of great help in clinical practice and is recommended. An important question is whether the disorder is continuously present or whether is it fluctuating. Fluctuating disorders point to a sinonasal (conductive) problem. Olfactory distortions most often present in females in the second to fifth decades of life. If a distortion is noted in the teens or twenties, a metabolic disorder should be suspected.21 It should also be noted whether the distortion is experienced during inhalation or exhalation and whether blocking one or both nostrils can eliminate it.

History: Gustation

Once again, a meticulous history is of great importance. The onset of the disorder—suddenly versus gradually—and any possible causative factors have to be evaluated. Concomitant diseases (renal, liver, other systemic diseases such as autoimmune diseases, etc.) should also be assessed, and a thorough medication history taken. Local factors such as the use of mouth irrigations or saliva problems should be assessed. If possible, the examiner should try to evaluate whether a quantitative or a predominantly qualitative disorder is present; however, qualitative disorders might also be accompanied by quantitative disorders, so a quantitative assessment should always be made. For more details about the history of gustatory disorders, see Chapter 15.