Smell and taste disorders in primary care.

Smell and taste disorders can be challenging to diagnose because of the large number of potential etiologies. Patients are often unable to provide a clear history of symptoms, because they frequently cannot distinguish between difficulties with smell and taste. Standardized questionnaires may be helpful in diagnosis. Smell and taste dysfunction have been implicated in loss of appetite, unintended weight loss, malnutrition, and reduced quality of life. Taste dysfunction may be complete or partial, and affect one or more aspects of taste (sweetness, bitterness, sourness, saltiness, and umami [savory]). An estimated 95% of taste disorders are caused by impairment of smell rather than gustatory loss. The most common causes of olfactory dysfunction include allergic rhinitis, chronic rhinosinusitis (with or without sinonasal polyps), and upper respiratory infection. Other potential causes include head trauma, neurodegenerative diseases (including Parkinson disease and cognitive impairments), and medications. Examination of the nose, mouth, and oropharynx as well as neurologic examination (focusing on cranial nerves I, VII, IX, and X) is essential. Additional assessment such as cognitive testing, nasal endoscopy, computed tomography of the sinuses or nose, or brain magnetic resonance imaging may be indicated. Up to one-half of patients with olfactory dysfunction improve over time. Improvement in olfactory function is inversely correlated with severity and duration of loss, age, smoking, and male sex.