ESSENTIALS OF DIAGNOSIS
Subjective diminished smell or taste sensation.
Lack of objective nasal obstruction.
Objective decrease in olfaction demonstrated by testing.
The physiology of olfaction remains less well understood than that of the other special senses. Odorant molecules traverse the nasal vault to reach the cribriform area and become soluble in the mucus overlying the exposed dendrites of receptor cells. Anatomic blockage of the nasal cavity with subsequent airflow disruption is the most common cause of olfactory dysfunction (hyposmia or anosmia). Polyps, septal deformities, and nasal tumors may be the cause. Transient olfactory dysfunction often accompanies the common cold, nasal allergies, and perennial rhinitis through changes in the nasal and olfactory epithelium. About 20% of olfactory dysfunction is idiopathic, although it often follows a viral illness. Hyposmia and anosmia are cardinal early manifestations of the COVID-19 illness caused by the novel SARS-CoV-2 coronavirus; the olfactory symptoms may linger and even be permanent sequelae of this viral infection. 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. Head trauma is a rare but severe cause of olfactory dysfunction. Shearing of the olfactory neurites accounts for less than 5% of cases of hyposmia but is more commonly associated with anosmia. Absent, diminished, or distorted smell or taste has been reported in a wide variety of endocrine, nutritional, and nervous disorders. As of 2020, acute olfactory dysfunction—even without other associated symptoms— should be considered as a presenting symptom of COVID-19 and merits immediate testing for SARS-CoV-2 infection.
Evaluation of olfactory dysfunction should include a thorough history of systemic illnesses and medication use as well as a physical examination focusing on the nose and nervous system. Nasal obstruction (from polyps, trauma, foreign bodies, or nasal masses) can cause functional hyposmia and should be excluded before concluding that the disruption of olfaction is primary. Most clinical offices are not set up to test olfaction, but such tests may at times be worthwhile if only to assess whether a patient possesses any sense of smell at all. The University of Pennsylvania Smell Identification Test (UPSIT) is available commercially and is a simple, self-administered “scratch-and-sniff” test that is useful in differentiating hyposmia, anosmia, and malingering. Odor threshold can be tested at regional specialty centers using increasing concentrations of various odorants.
Hyposmia secondary to nasal polyposis, obstruction, and chronic rhinosinusitis may respond to endoscopic sinus surgery. Unfortunately, there is no specific treatment for primary disruption of olfaction; some disturbances spontaneously resolve. The degree of hyposmia is the greatest predictor of recovery, with less severe hyposmia recovering at a much higher rate. In permanent hyposmia, counseling should be offered about seasoning foods (such as using pepper that stimulates the trigeminal as ...