Olfactory loss has been linked to a variety of causes and can profoundly influence a patient's quality of life.
It is estimated that functional anosmia has a prevalence of approximately 5% of the general population. Studies suggest that the prevalence of olfactory impairment in the adult population ranges from 0.6% in those aged <35 years to 13.9% among those aged ≥65 years (depending on the test method used, sample demographics, and definition of impairment).
In a cross-sectional sample of older American adults (mean age 68 years), approximately 22% were unable to identify four or more odors using a validated odor identification task. Older African Americans and Hispanics were more likely to suffer from olfactory dysfunction.
In patients presenting primarily for loss of smell, the most commonly identified etiologies include a prior viral upper respiratory infection, head trauma, and underlying chronic sinus inflammation. These 3 causes account for over 50% of patients.
Olfactory loss may occur as a sensorineural loss, following degenerative changes in the olfactory neuronal receptors or neuroepithelium in the olfactory cleft. It may also occur as a conductive loss following an obstruction or inflammation within the nasal vault that prevents access of odorants to the olfactory receptors.
Types of olfactory loss
The loss may be complete (anosmia) or partial (hyposmia). It may be associated with perceived odor distortions (dysosmia) that are related to actual environmental odorant stimulation (parosmia) or occur spontaneously (phantosmia).
Patients may present complaining of both smell and taste loss, or isolated taste loss, but on investigation their taste function is intact. This relates to the common confusion between taste and flavor. Taste sensation includes salt, sour, sweet, bitter, and umami (savory). Flavor perception is based upon olfactory, tactile, and thermal sensations as well as taste, with olfactory being arguably the most important of these sensations. The loss of olfactory input makes food generally unappealing, something most patients notice very quickly. However, a true measurable taste loss is distinctly uncommon.
For patients with olfactory loss due to an inflammatory process, reducing inflammation and obstruction in the nasal vault can effectively restore the ability to smell.
Unfortunately, in most cases of olfactory loss, no specific therapy is available. However, patients will continue to seek medical opinion until they feel a thorough workup has been performed and a thorough explanation has been provided. Some data suggest that olfactory training can increase the potential recovery after a postviral or post-traumatic olfactory loss.
Safety issues related to olfactory loss include the inability to detect gas leaks, fire, or spoiled foods. However, the most significant impact for each patient is typically the loss in quality of life related to eating and drinking. This can be devastating. In some cases it may result in diminished appetite and inadequate nutritional intake, and in other cases it can cause increased oral intake and weight gain as patients seek chemosensory satisfaction. These consequences can have a negative impact on associated medical conditions such as diabetes and high blood pressure. Invariably, patients receive little sympathy from friends and, on occasion, family and sometimes even from their physician.
For most patients who experience a loss of smell, no restorative therapy is available (unless the loss is secondary to inflammatory rhinosinusitis). Therefore, while most patients do benefit from counseling regarding safety issues and flavor enhancement methods, any information regarding prognosis becomes very important. Studies suggest prognosis relates more to the severity of the initial loss (as confirmed on objective olfactory testing), the age and sex of the patient, smoking, and the presence of dysosmia, than to the etiology of sensorineural loss.
- Viral upper respiratory infection
- Nasal polyps
- Chronic inflammatory sinus disease
- Frontal or occipital trauma
- Concussive injury caused by frontal or occipital blow to head
- Chemical exposure
- Drug exposure
- Radiation therapy of head and neck
- Alzheimer disease
- Parkinson disease
- Anterior craniotomy
- Craniofacial procedures
- Endoscopic sinus surgery
- Granulomatosis with polyangiitis
- Sjogren syndrome
- Sinonasal tumors
- Olfactory groove meningioma
- Turner syndrome
- Kallmann syndrome
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