> Table of Contents > Smell and Taste Disorders
Smell and Taste Disorders
Beth Mazyck, MD
Daniel B. Kurtz, PhD
image BASICS
DESCRIPTION
  • 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
EPIDEMIOLOGY
Incidence
There are ˜200,000 patient visits a year for smell and taste disturbances.
Prevalence
  • 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
    • Aging
    • 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)
    • Cigarette smoking
    • Cocaine abuse (intranasal)
    • Hemodialysis
    • 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
    • Gingivitis
    • 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, &bgr;-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
Genetics
May be related to underlying genetically associated diseases (Kallmann syndrome, Alzheimer disease, migraine syndromes, rheumatologic conditions, endocrine disorders)
RISK FACTORS
  • Age >65 years
  • Poor nutritional status
  • Smoking tobacco products
GENERAL PREVENTION
  • 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.
Geriatric Considerations
  • Elders are at particular risk of eating spoiled food or inadvertently being exposed to natural gas leaks owing to anosmia from aging.
  • Anosmia also may be an early sign of degenerative disorders and has been shown to predict increased 5-year mortality (1)[B].
Pediatric Considerations
  • 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 Considerations
  • 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
image DIAGNOSIS
Smell and taste disturbances are symptoms; it is essential to look for possible underlying causes.
PHYSICAL EXAM
Thorough HEENT exam
DIFFERENTIAL DIAGNOSIS
  • Epilepsy (gustatory aura)
  • Epilepsy (olfactory aura)
  • Memory impairment
  • Psychiatric conditions
DIAGNOSTIC TESTS & INTERPRETATION
Initial Tests (lab, imaging)
Consider (not all patients require all tests)
  • CBC
  • Liver function tests
  • Blood glucose
  • Creatinine
  • Vitamin B12 level
  • Thyroid-stimulating hormone (TSH)
  • Serum IgE
  • CT scanning is the most useful and cost-effective technique for assessing sinonasal disorders and is superior to an MRI in evaluating bony structures and airway patency. Coronal CT scans are particularly valuable in assessing paranasal anatomy (2)[B].
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Follow-Up Tests & Special Considerations
Diagnosis of smell and taste disturbances is usually possible through history; however, the following tests can be used to confirm:
  • Olfactory tests
    • Smell identification test: evaluates the ability to identify 40 microencapsulated scratch-and-sniff odorants (3)[B]
    • Brief smell identification test (4)[B]
    • Taste tests (more difficult because no convenient standardized tests are presently available): Solutions containing sucrose (sweet), sodium chloride (salty), quinine (bitter), and citric acid (sour) are helpful.
    • An MRI is useful in defining soft tissue disease; therefore, a coronal MRI is the technique of choice to image the olfactory bulbs, tracts, and cortical parenchyma. Possible placement of an accessory coil (TMJ) over the nose to assist in imaging.
image TREATMENT
GENERAL MEASURES
  • Appropriate treatment for underlying cause
  • Quit smoking (5)[B].
  • Treatment of underlying nasal congestion with nasal decongestants and/or nasal/oral steroids (6,7,8,9)[B]
  • Surgical correction of nasal blockage/nasal polyps (10)[B]
  • Some drug-related smell or taste loss or dysgeusias can be reversed with cessation of the offending medication, but it may take many months (11,12,13,14)[B].
  • Stop repeated oral trauma (e.g., appliances, tonguebiting behaviors).
  • Proper nutritional and dietary assessment (2)[C]
  • Formal dental evaluation
MEDICATION
  • Treat underlying causes as appropriate. Idiopathic cases will often resolve spontaneously.
  • Consider trial of corticosteroids topically (e.g., fluticasone nasal spray daily to BID) and/or systemically (e.g., oral prednisone 60 mg daily for 5 to 7 days) (6)[B].
  • Zinc and vitamins (A, B complex) when deficiency is suspected (15)[B]
ISSUES FOR REFERRAL
  • Consider referral to an otolaryngologist or neurologist for persistent cases.
  • Referral to a subspecialist at a regional smell and taste center when complex etiologies are suspected
SURGERY/OTHER PROCEDURES
If needed for treatment of underlying cause
image ONGOING CARE
DIET
  • Weight gain/loss is possible because the patient may reject food or may switch to calorie-rich foods that are still palatable.
  • Ensure a nutritionally balanced diet with appropriate levels of nutrients, vitamins, and essential minerals.
PATIENT EDUCATION
  • Caution patients not to overindulge as compensation for the bland taste of food. For example, patients with diabetes may need help in avoiding excessive sugar intake as an inappropriate way of improving food taste.
  • Patients with chemosensory impairments should use measuring devices when cooking and should not cook by taste.
  • Optimizing food texture, aroma, temperature, and color may improve the overall food experience when taste is limited.
  • Patients with permanent smell dysfunction must develop adaptive strategies for dealing with hygiene, appetite, safety, and health.
  • Natural gas and smoke detectors are essential; check for proper function frequently.
  • Check food expiration dates frequently; discard old food.
PROGNOSIS
  • In general, the olfactory system regenerates poorly after a head injury. Most patients who recover smell function following head trauma do so within 12 weeks of injury.
  • Patients who quit smoking typically recover improved olfactory function and flavor sensation.
  • Many taste disorders (dysgeusias) resolve spontaneously within a few years of onset.
  • Phantosmias that are flow-dependent may respond to surgical ablation of olfactory mucosa.
  • Conditions such as radiation-induced xerostomia and Bell palsy generally improve over time.
REFERENCES
1. Pinto JM, Wroblewski KE, Kern DW, et al. Olfactory dysfunction predicts 5-year mortality in older adults. PLoS One. 2014;9(10):e107541.
2. Malaty J, Malaty IA. Smell and taste disorders in primary care. Am Fam Physician. 2013;88(12): 852-859.
3. Doty RL, Shaman P, Dann M. Development of the University of Pennsylvania smell identification test: a standardized microencapsulated test of olfactory function. Physiol Behav. 1984;32(3): 489-502.
4. Jackman AH, Doty RL. Utility of a three-item smell identification test in detecting olfactory dysfunction. Laryngoscope. 2005;115(12):2209-2212.
5. Frye RE, Schwartz BS, Doty RL. Dose-related effects of cigarette smoking on olfactory function. JAMA. 1990;263(9):1233-1236.
6. Seiden AM, Duncan HJ. The diagnosis of a conductive olfactory loss. Laryngoscope. 2001;111(1):9-14.
7. Deems DA, Doty RL, Settle RG, et al. Smell and taste disorders, a study of 750 patients from the University of Pennsylvania Smell and Taste Center. Arch Otolaryngol Head Neck Surg. 1991;117(5): 519-528.
8. Apter AJ, Gent JF, Frank ME. Fluctuating olfactory sensitivity and distorted odor perception in allergic rhinitis. Arch Otolaryngol Head Neck Surg. 1999;125(9):1005-1010.
9. Mott AE, Cain WS, Lafreniere LG, et al. Topical corticosteroid treatment of anosmia associated with nasal and sinus disease. Arch Otolaryngol Head Neck Surg. 1977;123(4):367-372.
10. Olsson P, Stjärne P. Endoscopic sinus surgery improves olfacton in nasal polyposis, a multicenter study. Rhinology. 2010;48(2):150-155.
11. Naik BS, Shetty N, Maben EV. Drug-induced taste disorders. Eur J Intern Med. 2010;21(3):240-243.
12. Ackerman BH, Kasbekar N. Disturbances of taste and smell induced by drugs. Pharmacotherapy. 1997;17(3):482-496.
13. Cowart BJ. Taste dysfunction: a practical guide for oral medicine. Oral Dis. 2011;17(1):2-6.
14. Tuccori M, Lapi F, Testi A, et al. Drug-induced taste and smell alterations: a case/non-case evaluation of an Italian database of spontaneous adverse drug reaction reporting. Drug Saf. 2011;34(10):849-859.
15. Henkin RI, Martin BM, Agarwal RP. Efficacy of exogenous oral zinc in treatment of patients with carbonic anhydrase VI deficiency. Am J Med Sci. 1999;318(6):392-405.
Codes
&NA;
ICD10
  • R43.9 Unspecified disturbances of smell and taste
  • R43.1 Parosmia
  • R43.2 Parageusia
Clinical Pearls
&NA;
  • Smell disorders are often mistaken as decreased taste by patients.
  • Most smell loss is due nasal passage obstruction.
  • Actual taste disorders are often related to dental problems or medication side effects.
  • Gradual smell loss is very common in the elderly; extensive workup in this population may not be indicated if no associated signs/symptoms are present but may be predictive of 5-year mortality.