Chapter 030. Disorders of Smell, Taste, and Hearing (Part 6)

Approach to the Patient: Disorders of the Sense of Taste Patients who complain of loss of taste should be evaluated for both gustatory and olfactory function. Clinical assessment of taste is not as well developed or standardized as that of smell. The first step is to perform suprathreshold whole-mouth taste testing for quality, intensity, and pleasantness perception of four taste qualities: sweet, salty, sour, and bitter. Most commonly used reagents for taste testing are sucrose, citric acid or hydrochloric acid, caffeine or quinine (sulfate or hydrochloride), and sodium chloride. The taste stimuli should be freshly prepared and have similar...
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Chapter 030. Disorders of Smell, Taste, and Hearing (Part 6) Chapter 030. Disorders of Smell, Taste, and Hearing (Part 6) Approach to the Patient: Disorders of the Sense of Taste Patients who complain of loss of taste should be evaluated for bothgustatory and olfactory function. Clinical assessment of taste is not as welldeveloped or standardized as that of smell. The first step is to performsuprathreshold whole-mouth taste testing for quality, intensity, and pleasantnessperception of four taste qualities: sweet, salty, sour, and bitter. Most commonlyused reagents for taste testing are sucrose, citric acid or hydrochloric acid, caffeineor quinine (sulfate or hydrochloride), and sodium chloride. The taste stimulishould be freshly prepared and have similar viscosity. For quantification, detectionthresholds are obtained by applying graduated dilutions to the tongue quadrants orby whole-mouth sips. Electric taste testing (electrogustometry) is used clinically toidentify taste deficits in specific quadrants of the tongue. Regional gustatorytesting may also be performed to assess for the possibility of loss localized to oneor several receptor fields as a result of a peripheral or central lesion. The history ofthe disease and localization studies provide important clues to the causes of thetaste disturbance. For example, absence of taste on the anterior two-thirds of thetongue associated with a facial paralysis indicates that the lesion is proximal to thejuncture of the chorda tympani branch with the facial nerve in the mastoid. Disorders of the Sense of Taste: Treatment Treatment of gustatory disorders is limited. No effective therapies exist forthe sensorineural disorders of taste. Altered taste due to surgical stretch injury ofthe chorda tympani nerve usually improves within 3–4 months, while dysfunctionis usually permanent with transection of the nerve. Taste dysfunction followingtrauma may resolve spontaneously without intervention and is more likely to do sothan posttraumatic smell dysfunction. Idiopathic alterations of taste sensitivityusually remain stable or worsen; zinc and vitamin therapy are of unproven value.Directed therapy to address factors that affect taste perception can be of value.Xerostomia can be treated with artificial saliva, providing some benefit to patientswith a disturbed salivary milieu. Oral pilocarpine may be beneficial for a varietyof forms of xerostomia. Appropriate treatment of bacterial and fungal infections ofthe oral cavity can be of great help in improving taste function. Taste disturbancerelated to drugs can often be resolved by changing the prescribed medication. Hearing Hearing loss is one of the most common sensory disorders in humans andcan present at any age. Nearly 10% of the adult population has some hearing loss,and one-third of individuals >65 years have a hearing loss of sufficient magnitudeto require a hearing aid. Physiology of Hearing (Fig. 30-3) The function of the external and middle ear is to amplify soundto facilitate mechanotransduction by hair cells in the inner ear. Sound waves enterthe external auditory canal and set the tympanic membrane in motion, which inturn moves the malleus, incus, and stapes of the middle ear. Movement of the footplate of the stapes causes pressure changes in thefluid-filled inner ear eliciting a traveling wave in the basilar membrane of thecochlea. The tympanic membrane and the ossicular chain in the middle ear serveas an impedance-matching mechanism, improving the efficiency of energytransfer from air to the fluid-filled inner ear. Figure 30-3