n recent years, the importance and frequency of olfactory dysfunction has become apparent. Now known to affect approximately 20% of the general adult population, 1 impaired olfactory function can have a significant effect on quality of life through disordered eating behaviors, deficits in olfactory-mediated social behavior, and environmental hazard exposure. Although such effects are often more extreme in individuals relying professionally on their sense of smell, the more insidious effect of dysfunction leads to symptoms of depression in as many as 40% of patients. 2 Moreover, the physiological importance of smell is revealed by the association between olfactorydysfunctionanddisease.Olfactorydysfunctionisanearlybiomarker in many neurodegenerative conditions, including Alzheimer disease and Parkinson disease, and anosmia is more closely associated with 5-year mortality than myocardial infarction, cerebrovascular accident, diabetes, heart failure, or cancer. 3,4 Therefore, olfactory dysfunction should be diagnosed early, and treatment should be offered where available. The recent Position Paper on Olfactory Dysfunction 5 was published to provide guidance on the diagnosis, monitoring, and evidence-based manage-ment of olfactory impairment. In the following review, we provide an overview of the content of these guidelines.
Pathophysiology and Clinical Presentation
General Overview of SmellThe perception of smell requires activation of olfactory receptor neurons (collectively, cranial nerve I) found within the neuroepithelium of the olfactory cleft. Depending on the odor, this perception is usually accompanied by activation of the trigeminal nerve (cranial nerve V), which imparts varying amounts of heat, coolness, pungency, and irritation.Perceptionofodorstransmittedthroughthenoseduringbreathing or sniffing is termed orthonasal olfaction, whereas perception of those transmitted through the nasopharynx during eating is retronasal olfaction. Normal olfactory function is termed normosmia.Olfactorydysfunctionisbroadlydividedintoquantitativeandqualitative disorders. Quantitative dysfunction denotes reduced ability to perceive odors, without distortion in their quality. This type of dysfunc-IMPORTANCE Olfactory dysfunction affects approximately 20% of the general adult population. It is associated with reduced quality of life and important health care outcomes such as neurodegeneration and death. The accurate diagnosis of olfactory dysfunction is therefore important to quantify impairment, the effect of intervention, and residual disability. This review summarizes the current evidence on the diagnosis and management of olfactory dysfunction.OBSERVATIONS Olfactory dysfunction can be quantitative and/or qualitative. Despite numerous underlying pathophysiological causes, approximately two-thirds of cases are due to sinonasal disease or postinfectious or posttraumatic dysfunction. All patients should undergo assessment with a thorough clinical history and examination (including nasoendoscopy) followed by subjective olfactory a...