Anosmia is a topic covered in the 5-Minute Clinical Consult.

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Basics

Description

  • Anosmia is defined as the inability to detect odors. This condition can be temporary or permanent depending on the underlying pathology.
  • The sense of smell is necessary in determining the flavor of foods and beverages. It also aids in the detection of environmental hazards such as spoiled food, leaking natural gas, smoke, or airborne pollutants.
  • The human sense of smell is mediated by both cranial nerve I (CN I; olfactory nerve) and by cranial nerve V (CN V; trigeminal nerve).
    • Qualitative odor sensations (e.g., the smell of a flower or of spoiled food) are mediated by CN I.
    • The somatosensory components of odorants (e.g., warmth, coolness, sharpness, and irritation) are mediated by the ophthalmic and maxillary divisions of CN V.

Epidemiology

Incidence
There are >200,000 physician visits each year for chemosensory complaints.


Prevalence
  • Prevalent sex: male > female
  • Age-related deficits in olfaction are well documented (1), and the ability to detect odors slowly declines with age:
    • 1–2% in people <50 years
    • 24.5% in people 50 to 80 years
    • 62.5% in people >80 years

Etiology and Pathophysiology

  • Olfactory decline associated with aging (presbyosmia) is the most common cause of anosmia (1).
  • Anosmia not associated with presbyosmia is most often caused by nasal/sinus disease, an acute upper respiratory infection (URI), or head trauma.
  • Conductive defects:
    • Obstruction in the nasal cavity, caused by masses, may prevent flow of odorants to the olfactory epithelium:
      • Nasal polyps (most common)
      • Sinonasal papillomas
      • Certain developmental abnormalities (e.g., encephaloceles, dermoid cysts) may also cause obstruction.
      • Malignancy
    • In addition, patients with laryngectomies or tracheotomies sometimes experience hyposmia because of a reduced or absent nasal airflow.
  • Central and sensorineural defects:
    • Most olfactory defects are caused by inflammatory processes in the nasal cavity itself.
    • Chronic or acute rhinosinusitis (allergic, infectious, or toxic secondary to noxious stimuli) can lead to progressive damage of the olfactory mucosa, leading to a permanent decline in olfaction.
      • Viral infections
      • Sarcoidosis (affecting neural structures)
      • Granulomatosis with polyangiitis (Wegener granulomatosis)
      • Multiple sclerosis
    • Genetic causes (e.g., Kallmann syndrome)
    • Endocrine disorders
      • Hypothyroidism
      • Hypoadrenalism
      • Diabetes mellitus
    • Head trauma, stroke, brain surgery, or subarachnoid hemorrhage
      • Damage to olfactory bulbs or cortical lesions at the olfactory-related brain regions (e.g., amygdala, temporal lobe region, and frontal lobe region) can lead to posttraumatic anosmia.
    • Iatrogenic: toxicity from systemic or inhaled drugs (e.g., aminoglycosides, formaldehyde, alcohol, nicotine, organic solvents, or zinc nasal sprays)
    • Degenerative processes of the central nervous system (CNS) (2)
      • Parkinson disease
      • Alzheimer disease
      • Normal aging, also known as presbyosmia

Genetics
Anosmia may present as a symptom in certain genetically inherited disorders (Kallmann syndrome, migraine syndromes, rheumatologic conditions, endocrine disorders, and Alzheimer disease).

Risk Factors

  • Age >65 years
  • Poor nutrition
  • Smoking tobacco

General Prevention

  • Smoking cessation
  • Good oral hygiene and avoidance of noxious chemicals
  • Consuming a well-balanced diet

Commonly Associated Conditions

Chronic rhinosinusitis, URIs, migraines, and head trauma

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Citation

* When formatting your citation, note that all book, journal, and database titles should be italicized* Article titles in AMA citation format should be in sentence-case
TY - ELEC T1 - Anosmia ID - 117636 Y1 - 2019 PB - 5-Minute Clinical Consult, Updating UR - https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/117636/all/Anosmia ER -