ESSENTIALS OF DIAGNOSIS
Subjective diminished smell or taste sensation.
Lack of objective nasal obstruction.
Objective decrease in olfaction demonstrated by testing.
Odorant molecules traverse the nasal cavity to reach the cribriform area along the anterior skull base and become soluble in the mucus overlying the olfactory 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. Due to localized inflammation, 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. Olfactory dysfunction is an early manifestations of COVID-19; the olfactory symptoms may linger and even be permanent sequelae of this viral infection; however, few data are available on longevity of dysfunction. 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.
CNS neoplasms, especially those that involve the olfactory groove or temporal lobe, also may affect olfaction and should be considered in patients with no other explanation for their hyposmia. Head trauma is also a rare but severe cause of olfactory dysfunction due to shearing of the olfactory sensory cells. Head trauma accounts for less than 5% of cases of hyposmia but is more commonly associated with anosmia than with hyposmia. Absent, diminished, or distorted smell has been reported in a wide variety of endocrine, nutritional, and nervous disorders.
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 idiopathic. 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.
Olfactory dysfunction secondary to nasal polyposis, obstruction, and chronic rhinosinusitis may respond to surgically removing the anatomic blockage, as with endoscopic sinus surgery. Unfortunately, there is no specific treatment for primary disruption of olfaction; some disturbances spontaneously resolve. The degree of olfactory dysfunction is the greatest predictor of recovery, with less severe olfactory dysfunction recovering at a much higher rate. In permanent olfactory dysfunction, counseling should be offered ...