Smell and Taste Disorders
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- The senses of smell and taste allow a full appreciation of the flavor and palatability of foods and also serve as a warning system against toxins, polluted air, smoke, and spoiled food.
- Physiologically, the chemical senses aid in normal digestion by triggering GI secretions. Smell/taste dysfunction may have a significant impact on quality of life.
- Loss of smell occurs more frequently than loss of taste, and patients frequently confuse the concepts of flavor loss (as a result of smell impairment) with taste loss (an impaired ability to sense sweet, sour, salty, or bitter).
- Smell depends on the functioning of CN I (olfactory nerve) and CN V (trigeminal nerve).
- Taste depends on the functioning of CNs VII, IX, and X. Because of these multiple pathways, total loss of taste (ageusia) is rare.
- Systems affected: nervous, upper respiratory
There are ~200,000 patient visits a year for smell and taste disturbances.
- Predominant sex: male > female. Men begin to lose their ability to smell earlier in life than women.
- Predominant age: Chemosensory loss is age dependent:
- Age >80 years: 80% have major olfactory impairment; nearly 50% are anosmic.
- Ages 65 to 80 years: 60% have major olfactory impairment; nearly 25% are anosmic.
- Age <65 years: 1–2% have smell impairment.
- Estimated >2 million affected in the United States
Etiology and Pathophysiology
- Smell and/or taste disturbances:
- Nutritional factors (e.g., malnutrition, vitamin deficiencies, liver disease, pernicious anemia)
- Endocrine disorders (e.g., thyroid disease, diabetes mellitus, renal disease)
- Head trauma
- Migraine headache (e.g., gustatory aura, olfactory aura)
- Sjögren syndrome
- Toxic chemical exposure
- Industrial agent exposure
- Medications (see below)
- Neurodegenerative diseases (e.g., multiple sclerosis, Alzheimer disease, cerebrovascular accident, Parkinson disease)
- Infections (e.g., upper respiratory infection [URI], oral and perioral infections, candidiasis, coxsackievirus, AIDS, viral hepatitis, herpes simplex virus)
- Possible causes of smell disturbance:
- Nasal and sinus disease (e.g., allergies, rhinitis, rhinorrhea, URI)
- Cigarette smoking
- Cocaine abuse (intranasal)
- Radiation treatment of head and neck
- Congenital conditions
- Neoplasm (e.g., brain tumor, nasal polyps, intranasal tumor)
- Systemic lupus erythematosus (SLE)
- Bell palsy
- Oral/perioral skin lesion
- Damage to CN I/V
- Possible association with psychosis and schizophrenia
- Possible causes of taste loss:
- Oral appliances
- Dental procedures
- Intraoral abscess
- Damage to CN VI, IX, or X
- Stroke (especially frontal lobe)
- Selected medications that reportedly alter smell and taste:
- Antibiotics: amikacin, ampicillin, azithromycin, ciprofloxacin, clarithromycin, doxycycline, griseofulvin, metronidazole, ofloxacin, tetracycline, terbinafine, β-lactamase inhibitors
- Anticonvulsants: carbamazepine, phenytoin
- Antidepressants: amitriptyline, doxepin, imipramine, nortriptyline
- Antihistamines and decongestants: zinc-based cold remedies (Zicam)
- Antihypertensives and cardiac medications: acetazolamide, amiloride, captopril, diltiazem, hydrochlorothiazide, nifedipine, propranolol, spironolactone
- Anti-inflammatory agents: auranofin, gold, penicillamine
- Antimanic drugs: lithium
- Antineoplastics: cisplatin, doxorubicin, methotrexate, vincristine
- Antiparkinsonian agents: levodopa, carbidopa
- Antiseptic: chlorhexidine
- Antithyroid agents: methimazole, propylthiouracil
- Lipid-lowering agents: statins
May be related to underlying genetically associated diseases (Kallmann syndrome, Alzheimer disease, and other neurodegenerative disorders, migraine syndromes, rheumatologic conditions, endocrine disorders)
- Age >65 years
- Poor nutritional status
- Smoking tobacco products
- Eat a well-balanced diet, with appropriate vitamins and minerals.
- Maintain good oral and nasal health, with routine visits to the dentist.
- Do not smoke tobacco products.
- Avoid noxious chemical exposures/unnecessary radiation.
- Smell and taste disorders are uncommon in children in developed countries.
- In developing countries with poor nutrition (particularly zinc depletion), smell and taste disorders may occur.
- Delayed puberty in association with anosmia (± midline craniofacial abnormalities, deafness, or renal abnormalities) suggests the possibility of Kallmann syndrome (hypogonadotropic hypogonadism).
- Pregnancy is an uncommon cause of smell and taste loss or disturbances.
- Many women report increased sensitivity to odors during pregnancy as well as an increased dislike for bitterness and a preference for salty substances.
Commonly Associated Conditions
URI, allergic rhinitis, dental abscesses