Smell and Taste Disorders
- Physiologically, the senses of smell and taste aid in normal digestion by triggering GI secretions.
- 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:
- 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.
- Prior to the COVID-19 pandemic, an estimated >2 million people were affected in the United States
- Commonly occurs with SARS-CoV-2, the virus responsible for COVID-19
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)
- Migraine headache (e.g., gustatory aura, olfactory aura)
- Sjögren syndrome
- Toxic exposures
- Neurodegenerative diseases (e.g., multiple sclerosis, Alzheimer disease, cerebrovascular accident, Parkinson disease)
- Smell-specific disturbance:
- Nasal and sinus disease (e.g., allergies, rhinitis, rhinorrhea, URI)
- Cigarette smoking
- Cocaine abuse (intranasal)
- Neoplasm (e.g., brain tumor, nasal polyps, intranasal tumor)
- Systemic lupus erythematosus (SLE)
- Bell palsy
- Taste specific loss:
- Oral appliances, procedures
- Intraoral abscess, gingivitis
- Damage to CN VI, IX, or X
- Stroke (especially frontal lobe)
- Selected medications:
- 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
- Poor nutritional status
- Well-balanced diet
- Maintain good oral and nasal health.
- Avoid tobacco products and chemical exposures.
- 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).
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
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