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Smell and Taste Disorders

BASICS

  • Description:
  • Smell and taste aid digestion by triggering GI secretions.
  • Loss of smell is more frequent than loss of taste; patients often confuse loss of flavor (due to smell) with true taste loss (inability to sense sweet, sour, salty, or bitter).
  • Smell: CN I (olfactory) & CN V (trigeminal); Taste: CN VII, IX, X. Total ageusia (taste loss) is rare.
  • Systems affected: nervous, upper respiratory.

EPIDEMIOLOGY

  • ~200,000 visits/year for smell/taste disturbances.
  • Men lose smell earlier than women.
  • >80 yrs: 80% olfactory impairment; nearly 50% anosmic.
  • 65–80 yrs: 60% olfactory impairment; nearly 25% anosmic.
  • <65 yrs: 1–2% have smell impairment.

  • 2 million affected in the U.S. prior to COVID-19.

  • Very common with SARS-CoV-2 (COVID-19) infection.

ETIOLOGY & PATHOPHYSIOLOGY

  • Smell/Taste disturbances:
  • COVID-19: Common in mild (65%) & hospitalized (85%) cases. Sudden chemosensory loss predicts COVID-19.
  • Nutritional: Malnutrition, vitamin deficiencies, liver disease, pernicious anemia.
  • Endocrine: Thyroid disease, diabetes, renal disease.
  • Migraine, Sjögren syndrome, neurodegenerative diseases (Alzheimer, Parkinson, MS, stroke), toxic exposures, hemodialysis, SLE.
  • Nasal/Sinus disease: Allergies, rhinitis, URI, smoking, cocaine, neoplasms (nasal polyps/tumors), Bell palsy.
  • Taste-specific: Oral appliances, abscess, gingivitis, cranial nerve damage, frontal lobe stroke.
  • Medications: Multiple (see below).
  • Medications associated with loss:
  • Antibiotics (amikacin, ampicillin, azithro, etc.), anticonvulsants, antidepressants, antihistamines/decongestants, antihypertensives, anti-inflammatory agents, antineoplastics, antiparkinsonians, antimanics, antiseptics, antithyroid, lipid-lowering agents, statins.

RISK FACTORS

  • Poor nutrition
  • Smoking

GENERAL PREVENTION

  • Balanced diet
  • Oral/nasal hygiene
  • Avoid tobacco/chemical exposures

SPECIAL CONSIDERATIONS

  • Geriatrics:
  • Anosmia may be early sign of neurodegeneration; predicts increased 5-year mortality.
  • Pediatrics:
  • Poor nutrition (esp. zinc deficiency) can cause disorders.
  • Kallmann syndrome: Delayed puberty + anosmia.
  • Pregnancy:
  • Heightened odor sensitivity, more dislike of bitterness, preference for salty foods.

COMMONLY ASSOCIATED CONDITIONS

  • URI, allergic rhinitis, dental abscesses

DIAGNOSIS

  • Symptoms: Dry mouth/eyes, parotid swelling, arthralgia, myalgia, Raynaud, pulmonary/GI/renal/CNS symptoms.
  • History: URI, allergies, COVID-19 symptoms, oral pain, dental issues, cognitive/memory changes, medications, nutrition, weight change, infections, neurodegenerative disease.
  • Physical exam: Thorough HEENT assessment.

DIFFERENTIAL DIAGNOSIS

  • Epilepsy (gustatory/olfactory aura)
  • Memory impairment
  • Psychiatric conditions

DIAGNOSTIC TESTS

  • Initial:
  • SARS-CoV-2 test, CBC, chem panel, B12, TSH, IgE
  • CT (coronal): Best for sinonasal disease/anatomy
  • Follow-up:
  • Olfactory tests: 40-item or brief scratch-and-sniff identification tests
  • Taste tests: Solutions (sweet, salty, bitter, sour)
  • MRI (coronal): Olfactory bulbs, tracts, cortex
  • Dental exam, nutritional assessment

TREATMENT

  • General:
  • Address underlying cause (infections, nutrition, medication changes, surgical correction)
  • Smoking cessation, oral/nasal hygiene, treat nasal congestion (decongestants, nasal/oral steroids)
  • Drug-induced loss: Stop offending drug (may take months to recover)
  • Nutritional support (zinc, vitamins A/B as needed)
  • Medications:
  • Topical corticosteroids (fluticasone nasal spray daily–BID)
  • Short course oral steroids (prednisone 60 mg daily ×5–7 days)
  • Persistent cases:
  • Consider ENT or neurology referral

ONGOING CARE & PATIENT EDUCATION

  • Diet: Balanced, monitor weight
  • Advice:
  • Avoid excess sugar/salt for compensation (esp. in diabetes)
  • Use measuring tools for cooking; avoid cooking by taste alone
  • Enhance food with texture, aroma, temp, color
  • Permanent smell loss: Use smoke/gas detectors, check food expiry
  • Routine oral/dental care

PROGNOSIS

  • COVID-19–related smell loss:
  • Recovery: 74% (30d), 86% (60d), 90% (90d), 96% (120d)
  • Some develop phantosmia/parosmia (phantom/foul smells)
  • Head trauma: Most recover within 12 wks if at all
  • Smoking: Function improves with cessation
  • Taste disorders: Many resolve spontaneously over years

COMPLICATIONS

  • Permanent loss of smell/taste
  • Psychiatric symptoms (dysgeusia, phantosmia)

ICD-10

  • R43.9: Unspecified disturbance of smell and taste
  • R43.1: Parosmia
  • R43.2: Parageusia

CLINICAL PEARLS

  • Smell loss can be the first/only symptom in mild COVID-19.
  • Patients often mistake smell loss for taste loss.
  • Most temporary smell loss = nasal passage obstruction.
  • True taste loss often due to dental/medication issues.
  • Gradual smell loss common in elderly; extensive workup not always indicated.
  • Sudden unexplained smell loss: Think COVID-19.