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For further information, see CMDT Part 8-12: Olfactory Dysfunction

Key Features

Essentials of Diagnosis

  • Subjective diminished smell or taste sensation

  • Lack of objective nasal obstruction

  • Objective decrease in olfaction demonstrated by testing

General Considerations

  • Causes include

    • Anatomic blockage of the nasal cavity with subsequent airflow disruption (hyposmia or anosmia)

    • Polyps

    • Septal deformities

    • Nasal tumors

    • SARS-CoV-2 viral infection (COVID-19 illness)

    • Head trauma (rare but severe cause)

    • Shearing of the olfactory neurites

      • Accounts for < 5% of cases of hyposmia

      • More commonly associated with anosmia

  • Transient olfactory dysfunction often accompanies the common cold, nasal allergies, and perennial rhinitis

  • About 20% of olfactory dysfunction is idiopathic, although it often follows a viral illness

  • Central nervous system neoplasms, especially those that involve the olfactory groove or temporal lobe, may affect olfaction and must be considered in patients with no other explanation for their hyposmia or for other neurologic signs

  • Absent, diminished, or distorted smell or taste has been reported in a wide variety of endocrine, nutritional, and nervous disorders

Clinical Findings

  • Hyposmia and anosmia are cardinal early manifestations of COVID-19

  • Nasal obstruction (from polyps, trauma, foreign bodies, or nasal masses)

    • Can cause functional hyposmia

    • Should be excluded before concluding that the disruption of olfaction is primary

Diagnosis

  • In current pandemic, oropharyngeal or nasal swab PCR testing for SARS-CoV-2 virus (cause of COVID-19 illness) should be done

  • The University of Pennsylvania Smell Identification Test (UPSIT)

    • A simple, self-administered "scratch-and-sniff" test that is useful in differentiating hyposmia, anosmia, and malingering

    • Available commercially

  • Odor threshold can be tested at regional specialty centers using increasing concentrations of various odorants

Treatment

  • Endoscopic sinus surgery may be beneficial when hyposmia is secondary to nasal polyposis, obstruction, and chronic rhinosinusitis

  • Unfortunately, there is no specific treatment for primary disruption of olfaction or for olfactory disorder due to SARS-CoV-2 viral infection

Outcome

Prognosis

  • The degree of hyposmia is the greatest predictor of recovery, with less severe hyposmia recovering at a much higher rate; some cases spontaneously resolve

  • The olfactory symptoms of COVID-19 may linger and even be permanent sequelae

  • In permanent hyposmia, counseling should be offered about

    • Seasoning foods (such as using pepper that stimulates the trigeminal as well as olfactory chemoreceptors, rather than table salt)

    • Safety issues (such as installing home smoke alarms and using electric rather than gas appliances)

References

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D'Ascanio  L  et al. Olfactory dysfunction in COVID-19 patients: prevalence and prognosis for recovering sense of smell. Otolaryngol Head Neck Surg. 2021;164:82.
[PubMed: 32662745]  
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Doty  RL. Age-related deficits in taste and smell. Otolaryngol Clin North Am. 2018;51:815.
[PubMed: 30001793]  
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Howell  J ...

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