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 should be considered in patients with no other explanation for their hyposmia

• 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 idiopathic

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

• Surgically removing the anatomic blockage may be beneficial when olfactory dysfunction 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 olfactory dysfunction is the greatest predictor of recovery, with less severe olfactory dysfunction 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 olfactory dysfunction, 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