Chapter 030. Disorders of Smell, Taste, and Hearing (Part 3)

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Approach to the Patient: Disorders of the Sense of Smell Unilateral anosmia is rarely a complaint and is only recognized by testing of smell in each nasal cavity separately. Bilateral anosmia, on the other hand, brings patients to medical attention. Anosmic patients usually complain of a loss of the sense of taste even though their taste thresholds may be within normal limits. In actuality, they are complaining of a loss of flavor detection, which is mainly an olfactory function. The physical examination should include a thorough inspection of the ears, upper respiratory tract, and head and neck. A neurologic...

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Chapter 030. Disorders of Smell, Taste, and Hearing (Part 3) Approach to the Patient: Disorders of the Sense of Smell Unilateral anosmia is rarely a complaint and is only recognized by testing of smell in each nasal cavity separately. Bilateral anosmia, on the other hand, brings patients to medical attention. Anosmic patients usually complain of a loss of the sense of taste even though their taste thresholds may be within normal limits. In actuality, they are complaining of a loss of flavor detection, which is mainly an olfactory function. The physical examination should include a thorough inspection of the ears, upper respiratory tract, and head and neck. A neurologic examination emphasizing the cranial nerves and cerebellar and sensorimotor function is essential. Any signs of depression should be noted.
Sensory olfactory function can be assessed by several methods. The Odor Stix test uses a commercially available odor-producing magic marker–like pen held approximately 8–15 cm (3–6 in.) from the patient's nose. The 30-cm alcohol test uses a freshly opened isopropyl alcohol packet held ~30 cm (12 in.) from the patient's nose. There is a commercially available scratch-and-sniff card containing three odors available for gross testing of olfaction. A superior test is the University of Pennsylvania Smell Identification Test (UPSIT). This consists of a 40-item, forced choice, scratch-and-sniff paradigm. For example, one of the items reads, "This odor smells most like (a) chocolate, (b) banana, (c) onion, or (d) fruit punch." The test is highly reliable, is sensitive to age and sex differences, and provides an accurate quantitative determination of the olfactory deficit. The UPSIT, which is a forced-choice test, can also be used to identify malingerers who typically report fewer correct responses than would be expected by chance. The average score for total anosmics is slightly higher than that expected on the basis of chance because of the inclusion of some odorants that act by trigeminal stimulation. Olfactory threshold testing is another method of assessing olfactory function. Following assessment of sensory olfactory function, the detection threshold for an odorant such as methyl ethyl carbinol is established using graduated concentrations for each side of the nose. Nasal resistance can also be measured with anterior rhinomanometry for each side of the nose.
CT or MRI of the head is required to rule out paranasal sinusitis; neoplasms of the anterior cranial fossa, nasal cavity, or paranasal sinuses; or unsuspected fractures of the anterior cranial fossa. Bone abnormalities are best seen with CT. MRI is the most sensitive method to visualize olfactory bulbs, ventricles, and other soft tissue of the brain. Coronal CT is optimal for assessing cribriform plate, anterior cranial fossa, and sinus anatomy. Biopsy of the olfactory epithelium is possible. However, given the widespread degeneration of the olfactory epithelium and intercalation of respiratory epithelium in the olfactory area of adults with no apparent olfactory dysfunction, biopsy results must be interpreted with caution. Disorders of the Sense of Smell: Treatment Therapy for patients with transport olfactory losses due to allergic rhinitis, bacterial rhinitis and sinusitis, polyps, neoplasms, and structural abnormalities of the nasal cavities can be undertaken with a high likelihood for improvement. Allergy management; antibiotic therapy; topical and systemic glucocorticoid therapy; and surgery for nasal polyps, deviation of the nasal septum, and chronic hyperplastic sinusitis are frequently effective in restoring the sense of smell. There is no proven treatment for sensorineural olfactory losses. Fortunately, spontaneous recovery often occurs. Zinc and vitamin therapy (especially with vitamin A) are advocated by some. Profound zinc deficiency can
produce loss and distortion of the sense of smell but is not a clinically important problem except in very limited geographic areas (Chap. 71). The epithelial degeneration associated with vitamin A deficiency can cause anosmia, but in western societies the prevalence of vitamin A deficiency is low. Exposure to cigarette smoke and other airborne toxic chemicals can cause metaplasia of the olfactory epithelium, and spontaneous recovery can occur if the insult is removed. Counseling of patients is therefore helpful in such cases. More than half of people over age 60 suffer from olfactory dysfunction. No effective treatment exists for presbyosmia, but patients are often reassured to learn that this problem is common in their age group. In addition, early recognition and counseling can help patients to compensate for the loss of smell. The incidence of natural gas–related accidents is disproportionately high in the elderly, perhaps due in part to the gradual loss of smell. Mercaptan, the pungent odor in natural gas, is an olfactory stimulant that does not activate taste receptors. Many elderly with olfactory dysfunction experience a decrease in flavor sensation and find it necessary to hyperflavor food, usually by increasing the amount of salt in their diet. Taste
Compared with disorders of smell, gustatory disorders are uncommon. Loss of olfactory sensitivity is often accompanied by complaints of loss of the sense of taste, usually with normal detection thresholds for taste.