Smell and Taste Disorders

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Olfaction

The organs of olfaction are unique within the human body because they contain neuroepithelium that regenerates. However, these delicate nerve fibers may also be damaged and undergo permanent loss. Grossly, the nasal passages contain the structures of olfaction, which include the upper nasal septum, and middle and superior turbinates. These structures facilitate airflow and contain the primary olfactory neurons. Olfactory molecules dissolve in mucous overlying these neurons and then interact

Physiology of smell

Nasal airflow plays an integral part of smell detection. Although olfactory particles can contact the olfactory cleft by diffusion, airflow is generally a prerequisite of olfaction. As airflow distributes itself in the nasal cavity, about 15% flows to the olfactory cleft (Fig. 6). Smell is typically thought of as being mediated through nasal inhalation with orthonasal flow. Another contributor to olfaction and food flavor perception is retronasal olfaction, which occurs during ingestion of

Physiology of taste

Traditionally, taste is subdivided into 5 major gustatory classifications: salty, sweet, bitter, sour, and umami. In the taste buds, the chemical molecules are transformed into electrical signals that travel to the nucleus solitarius (medulla), to the ventricular posterior medial nucleus in the thalamus and to the parietal lobe, and give the perception of gustation.

Another integral component of gustation is the pleasure related to the oral sensation and tastes of the food ingested. Genetics

Clinical History of Olfactory or Taste Loss

A discussion with the patient while obtaining a history is useful for identifying the onset, symptoms, and duration of smell and taste changes. The patient may not disclose an olfactory disturbance unless directly asked. Associated clinical clues such as preceding trauma or viral infection are helpful in determining the cause of the perceived loss. According to rough projections, at least 1% of patients have an unrecognized loss.31 One study found that up to 16% of the general population has an

Olfactory Testing

Two classes of testing are available: electrophysical and psychophysical tests; however, psychophysical tests are more useful in the interoffice setting, more widely used, simple, and easy for the plastic rhinoplasty surgeon to use.33 Electrophysical tests are generally reserved for research studies. Testing olfaction documents not only the extent of the olfactory loss but also allows for comparisons during clinical follow-up and assessment for improvement over time (duration of deficit).

History

Patients presenting with a complaint of taste disturbance should be asked about any associated disorder of smell; any preexisting medical conditions and their treatment, such as ear infection, ear surgery, Bell palsy, significant head injury, recent upper respiratory tract illness, and various dental procedures or prostheses.47 A detailed medication history also should be obtained.

In addition to a physical examination and testing of taste and smell, special attention should be paid to the oral

After Upper Respiratory Infection

Many patients report temporary decreased smell during upper respiratory infection (URI), which is largely mediated by acute nasal edema and decrease of airflow during a viral infection. The nasal membrane edema commonly abates within a few days and smell returns to baseline. However, in a subset of patients, there is permanent olfactory loss following URI and the prognosis is principally poor, with only one-third recovering.50 In these patients a sensorineural insult occurs to the primary

Treatment of olfactory loss

A patient’s quality of life is affected after an olfactory loss, from enjoying a meal to safety around toxic chemicals. However, olfactory losses are often irreversible and lack proven therapeutic treatments. Determining the cause of the olfactory deficit is imperative in counseling the patient and predicting the likelihood of improvement. Sensorineural losses are less likely to recover, whereas conductive losses, for example obstructive nasal polyps, are more easily treatable.

Conductive smell

Future implications for olfaction loss

Much is known about the link between neurodegenerative disorders and olfaction, and this relationship may one day serve as a screening tool or early diagnostic test Alzheimer disease or Parkinson disease. The pathophysiology is still being investigated. Nonetheless, the senses of taste and smell offer unique opportunities in diagnosis and treatment of neurocognitive conditions and obesity-related ingestive behaviors.

In summary: olfaction and taste

Olfaction and taste promote satisfaction and protection in daily life. The astute facial plastic surgeon recognizes the importance of establishing a baseline smell test to document the patients’ olfactory status before surgery. After surgery, the surgeon must be alert to the possible mechanisms of hyposmia and anosmia and the pertinent treatment strategies. The surgeon must also understand the importance of counseling the patient and family regarding the cause of the dysfunction and the proper

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      Abnormalities in transport (inability of the tastant to reach the receptor), gustatory unit (abnormality of peripheral sensory organs), and neuronal unit (such as damage to the peripheral or central nervous system) are the mechanisms of such gustatory dysfunctions.92,95-97 In the oral cavity, the gustatory receptors can be exposed to pathologies (such as inflammation) or artificial restorative dental materials (such as acrylic) and can thereby affect gustation.92,98-100 Several genes and their associated receptors (for example, ENaC, T1R, T2R, TAS2R, and TRPV1) have been identified as coding for specific taste sensations.25,45,108-114

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      Smell is a fundamental sensation for having a standard life and for recognising dangerous odours that may threaten life. Viral infection of upper respiratory tract may result in olfactory impairment or smell disorders of various intensities and duration (Allis and Leopold, 2012). The incidence of anosmia is 70% in patients having different virus infections such as rhinovirus, adenovirus, influenza and parainfluenza virus (Suzuki et al., 2007).

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      Smell and taste are essential sensory functions both for good quality of life and for its preservation, by identifying several harmful odors and flavors. Viral Upper Respiratory Tract Infections (URTIs) can lead to Olfactory (OD) and Gustatory (GD) Disorders of varying degrees and duration,1 which can also occur in 70% of cases caused by rhinovirus, influenza virus and parainfluenza, respiratory syncytial virus, adenovirus and the severe acute respiratory syndrome virus (SARS-CoV-2).2 Coronavirus disease 2019 (COVID-19) became a viral pandemic that emerged from East Asia due to SARS-CoV-2.3

    • Autistic traits impact on olfactory processing in adolescent girls with Anorexia Nervosa restricting type

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      Anyway, all the correlations between “Attention Problems” and the olfactory scores resulted not significant for both AN and controls, proving a lack of effect for this possible confounding factor on the smell capabilities of the subjects enrolled. The main aim of the present study was to investigate the olfactory function in young females with recent-onset AN-R. Indeed, it is well known that chemosensory channels (smell and taste) are somehow related to each other (Freitas et al., 2018), both promoting satisfaction and protection in daily life (Allis and Leopold, 2012), and involved in reward mechanisms within eating disorders (Alonso-Alonso, 2013; Soussignan et al., 2012). However, according to previous literature analyzing whether smell and taste channels are affected in eating disorders, to which AN-R is a particularly important disturbance, the olfactory function appears to be more sensitive than the gustatory function with respect to physiopathological characteristics of AN (Fernández-Aranda et al., 2016).

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    Funding and disclosures: No funding support was obtained. Dr Allis has no financial disclosures or conflicts of interest. Dr Leopold is a consultant for: Neilmed Corp; Entellus Medical, Inc; Optinose US, Inc.

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