Chapter 030. Disorders of Smell, Taste, and Hearing (Part 5) pptx

Disorders of Smell, Taste, and Hearing Part 5 Disorders of the Sense of Taste Disorders of the sense of taste are caused by conditions that interfere with the access of the tastant to

Chapter 030 Disorders of Smell,

Taste, and Hearing

(Part 5)

Disorders of the Sense of Taste

Disorders of the sense of taste are caused by conditions that interfere with the access of the tastant to the receptor cells in the taste bud (transport loss), injure receptor cells (sensory loss), or damage gustatory afferent nerves and central gustatory pathways (neural loss) (Table 30-2)

Transport gustatory losses result from xerostomia due to many causes,

including Sjögren's syndrome, radiation therapy, heavy-metal intoxication, and bacterial colonization of the taste pore

Sensory gustatory losses are caused by inflammatory and degenerative

diseases in the oral cavity; a vast number of drugs, particularly those that interfere with cell turnover such as antithyroid and antineoplastic agents; radiation therapy

to the oral cavity and pharynx; viral infections; endocrine disorders; neoplasms; and aging

Neural gustatory losses occur with neoplasms, trauma, and surgical

procedures in which the gustatory afferents are injured Taste buds degenerate when their gustatory afferents are transected but remain when their somatosensory afferents are severed Patients with renal disease have increased thresholds for sweet and sour tastes, which resolves with dialysis

Table 30-2 Causes of Gustatory Dysfunction

Transport Gustatory Losses

Drugs

Heavy-metal intoxication

Radiation therapy

Sjögren's syndrome

Neural Gustatory Losses

Diabetes mellitus

Hypothyroidism

Oral neoplasms

Oral surgery

Sensory Gustatory Losses

Aging

Candidiasis

Drugs (antithyroid and antineoplastic)

Endocrine disorders

Oral neoplasms

Pemphigus

Radiation therapy

Viral infections (especially with

herpes viruses)

Radiation therapy

Renal disease

Stroke and other CNS disorders

Trauma

Upper respiratory tract infections

A side effect of medication is the single most common cause of taste dysfunction in clinical practice Xerostomia, regardless of the etiology, can be associated with taste dysfunction

It is associated with poor oral clearance and poor dental hygiene and can adversely affect the oral mucosa, all leading to dysgeusia However, severe salivary gland failure does not necessarily lead to taste complaints

Xerostomia, the use of antibiotics or glucocorticoids, or immunodeficiency

can lead to overgrowth of Candida; overgrowth alone, without thrush or overt

signs of infection, can be associated with bad taste or hypogeusia When taste dysfunction occurs in a patient at risk for fungal overgrowth, a trial of nystatin or other antifungal medication is warranted

Upper respiratory infections and head trauma can lead to both smell and taste dysfunction; taste is more likely to improve than smell The mechanism of taste disturbance in these situations is not well understood

Trauma to the chorda tympani branch of the facial nerve during middle ear surgery or third molar extractions is relatively common and can cause dysgeusia Bilateral chorda tympani injuries are usually associated with hypogeusia, whereas unilateral lesions produce only limited symptoms

As noted above, aging itself may be associated with reduced taste sensitivity The taste dysfunction may be limited to a single compound and may be mild