Loss of Smell

Aka: Loss of Smell, Smell Dysfunction, Anosmia, Hyposmia, Parosmia, Olfactory Dysfunction

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II. Epidemiology

  1. Olfactory Dysfunction U.S. Prevalence: 23% in age >40 years (39% in age >80 years)
    1. Rawai (2016) Chem Senses 41(1): 69-76 [PubMed]

III. Physiology

  1. See Smell Sensation
  2. See Taste Sensation

IV. Definitions

  1. Anosmia
    1. Sense of Smell lost completely
  2. Hyposmia
    1. Reduced Sense of Smell
  3. Parosmia
    1. Distorted Sense of Smell (WITH external odor stimulus)
  4. Phantosmia
    1. Olfactory Hallucination (WITHOUT external odor stimulus)

V. Risk Factors

  1. Advancing age
  2. Male gender
  3. Tobacco Abuse

VI. History

  1. Associated Symptoms
    1. Nose or sinus symptoms
      1. Rhinorrhea
      2. Sinusitis
      3. Nasal Polyps
      4. Acute Upper Respiratory Infection
    2. Mouth symptoms (if altered Taste Sensation)
      1. See Burning Mouth Syndrome
      2. See Pharyngitis
      3. See Xerostomia
      4. Dental Disorders (e.g. Gingivitis)
  2. Possible Triggers
    1. Facial Trauma
    2. Medications
      1. See Drug-Induced Olfactory Dysfunction
  3. Past Medical History
    1. Neurologic disorders (e.g. Parkinsonism, Dementia)

VII. Exam: General

  1. Nasopharynx (Anterior rhinoscopy)
    1. Allergic Rhinitis
    2. Sinusitis
    3. Nasal Polyposis
  2. Oral pharynx
    1. Xerostomia
    2. Oral Candidiasis
    3. Gingivitis or Periodontal Disease
    4. Glossitis
  3. Neurologic Exam
    1. Test Cranial Nerve 7, Cranial Nerve 9 and Cranial Nerve 10
    2. Cognitive Exam
    3. Motor Exam

VIII. Exam: Screening for Olfactory Dysfunction (Cranial Nerve I)

  1. Confirm that nares are patent prior to testing
  2. Patient closes eyes and occludes one nare
    1. Test for recognition of common substances
    2. Examples: Cloves, coffee, soap, vanilla, rose
    3. Various prepared items are available that give off odor (Quick Sticks, q-Sticks, Sniffin' Sticks)

IX. Imaging

  1. Nasolaryngoscopy
  2. Maxillofacial Sinus CT
  3. Consider Head CT or Brain MRI

X. Causes: Loss of Smell due to Local Nasal Causes (most common)

  1. Allergic Rhinitis
  2. Upper Respiratory Infection (post-viral Olfactory Dysfunction)
    1. Influenza
    2. Covid19
  3. Nasal Polyposis
  4. Sinusitis
  5. Other less common local causes
    1. Nasal surgery (e.g. septoplasty, Sinus Surgery)
    2. Tonsillectomy
    3. Head and neck radiation

XI. Causes: Loss of Smell due to Neurologic Conditions (common)

  1. Head Trauma
    1. Injury to Cribiform Plate (especially shearing force)
    2. Maxillofacial Trauma
  2. Neurodegenerative disorders
    1. Multiple Sclerosis
    2. Parkinson's Disease
    3. Alzheimer's Disease
  3. Other uncommon neurologic causes
    1. Frontal tumor
    2. Korsakoff's Psychosis
    3. Cerebrovascular Accident
    4. Intracranial Hemorrhage
    5. Lewy Body Dementia
    6. Multisystem Atrophy
    7. Huntington Disease
    8. Wilson Disease
    9. Friedreich Ataxia
    10. Spinocerebellar Ataxia
    11. Creutzfeldt-Jakob Disease

XII. Causes: Loss of Smell due to Systemic Conditions (less common causes)

  1. Pregnancy
  2. Organ failure
    1. Renal Failure
    2. Hepatic failure
  3. Infectious Disease
    1. Viral Hepatitis
    2. HIV Infection
    3. Herpes Encephalitis
  4. Endocrine disorders
    1. Cushing's Syndrome
    2. Addison Disease
    3. Hypothyroidism
    4. Diabetes Mellitus
  5. Rheumatologic Conditions
    1. Sjogren Syndrome
    2. Systemic Lupus Erythematosus
    3. Sarcoidosis
  6. Malnutrition or Vitamin Deficiency
    1. Vitamin B12 Deficiency
    2. Vitamin B6 Deficiency
    3. Zinc Deficiency
    4. Copper Deficiency
    5. Vitamin A Deficiency
    6. Niacin Deficiency
  7. Genetic disorders
    1. Kallmann's Syndrome
  8. Psychiatric Disorders
    1. Anorexia Nervosa
    2. Major Depression
    3. Bipolar Disorder
    4. Schizophrenia
  9. Substances of abuse
    1. Tobacco smoke
    2. Alcohol Abuse
    3. Amphetamines
    4. Topical Cocaine
  10. Medications
    1. See Drug-Induced Olfactory Dysfunction
  11. Toxins
    1. Hydrocarbons
      1. Benzene
      2. Gasoline
      3. Paint solvents
      4. Formaldehyde
    2. Heavy Metals
      1. Iron Poisoning
      2. Cadmium
      3. Chromium
      4. Lead Poisoning
      5. Mercury
      6. Welding agents
    3. Miscellaneous chemicals
      1. Acrylates
      2. Ammonia
      3. Salon chemicals (hair dressing)
      4. Sulfuric Acid

XIII. Management: Approach

  1. Distinguish Gustatory Dysfunction from Olfactory Dysfunction
    1. Olfactory Dysfunction in 95% of cases
  2. Evaluate for specific cause
    1. Consider olfactory testing (see exam above) if available
    2. Eliminate reversible causes (see above)
    3. Consider medication causes
      1. See Drug-Induced Olfactory Dysfunction
      2. See Medication Causes of Dry Mouth
    4. Smoking Cessation
      1. Olfactory function does not fully return to non-smoking levels for 15 years after cessation
      2. Vascular disease may further prolong recovery (up to 20 years)
      3. Passive Smoke Exposure appears to have inconsistent effects
  3. Evaluate and treat nasal and sinus disorders
    1. Consider Nasal Corticosteroid trial for 8 weeks
      1. Indicated for suspected Allergic Rhinitis, Chronic Sinusitis or Nasal Polyposis
      2. Sinwani (2019) Am J Rhinol Allergy 33(1): 69-82 [PubMed]
    2. Consider otolarygology Consultation
    3. Consider Sinus CT
    4. Consider post Head Trauma related causes
      1. MRI Brain may demonstrate Olfactory Bulb related changes
  4. Covid19 Related Olfactory Dysfunction
    1. No treatment (e.g. Intranasal Steroids) found effective in speeding olfactory recovery
    2. Improves or resolves more quickly than other causes
    3. Resolution by 7 days in a majority of patients and by 3 months in 80%
      1. Course prolonged in more severe disease
      2. Ferrell (2022) Eur Arch Otorhinolaryngol 279(9): 4633-40 [PubMed]
  5. Evaluate for neurodegenerative disease
    1. Parkinsonism is highly associated with Olfactory Dysfunction (95% of patients, 70% have Anosmia or Hyposmia)
      1. Olfactory Dysfunction may precede the diagnosis of motor dysfunction in Parkinsonism by up to 6 years
    2. Consider neurology Consultation
    3. Consider Brain MRI
  6. Symptomatic management
    1. Consider Olfactory Training twice daily before meals for 12 weeks
      1. See Olfactory Training
      2. Involves smelling 4 odors (e.g. rose, eucalyptus, Lemon, Clove)
      3. Hummel (2009) Laryngoscope 119(3) 496-9 [PubMed]

XIV. Complications

  1. Malnutrition and Unintentional Weight Loss
  2. Insomnia
  3. Safety Risk
    1. Lost ability to identify toxic odors (natural gas, smoke)
    2. Review with patients safety plans for home and work to compensate for Loss of Smell
  4. Depressed Mood
    1. Sivam (2016) Chem Senses 41(4): 293-9 [PubMed]

XV. Resources

  1. Smell and Taste Association of North America
    1. https://thestana.org/

XVI. References

  1. Baloh in Goldman (2000) Cecil Medicine, p. 2249-50
  2. Snow in Wilson (1991) Harrison's Internal Med, p. 152
  3. Malaty (2013) Am Fam Physician 88(1): 852-9 [PubMed]
  4. Savard (2023) Am Fam Physician 108(3): 240-8 [PubMed]

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