In adults, the two most common causes of smell problems that we see at our Clinic are: (1) Smell loss due to an ongoing process in the nose and/or sinuses such as nasal allergies and (2) smell loss due to injury of the specialized nerve tissue at the top of the nose (or possibly the higher smell pathways in the brain) from a previous viral upper respiratory infection. Individuals who lose their sense of smell as a result of a respiratory virus generally give us a very clear history of dating their smell loss from a time when they were experiencing cold or flu symptoms. These patients are typically in the older age groups. The smell loss is partial rather than total for many, and can be associated with taste loss, parosmias and/or dysgeusias. There is no known effective therapy for taste and/or smell problems due to presumed viral damage. Specifically, treatment with zinc is not recommended because it was not demonstrated to be any more effective than placebo. Some patients will recover function with time. We have followed some individuals with this disorder long-term. Of these, only 18 percent significantly improved their smell function on retesting. Improvement was gradual. Although this low improvement rate is discouraging, it should be remembered that we typically see the worst cases here at the Taste and Smell Clinic. There are probably many individuals out in the community who lost their sense of smell as a result of a virus and recovered it within short periods of time.
The other most common cause of smell loss is that due to an ongoing process in the nose and/or sinuses, specifically rhinitis (inflammation in the nose), nasal polyps and/or sinusitis. The history usually is that of gradual loss of smell ability proceeding to total loss. Recurrent, rapid, temporary improvement in the ability to smell, often after exercise or showering, is often reported. Some patients report temporary improvement with medications, such as antibiotics or corticosteroids. True taste loss does not occur, but patients sometimes report the presence of foul tastes/smells. Other important features include difficulty breathing through the nose, post nasal drip, nasal allergies, and a history of sinusitis and/or nasal polyps. Chronic sinusitis may present with smell loss and no other chronic symptoms, however.
In people who date the onset of smell loss to a viral infection, it can be difficult discerning between viral damage and an ongoing process in the nose and/or sinuses as the cause of the loss. Viral infection can lead to sinusitis in susceptible patients. This group of patients will have sinusitis as a key feature of their smell loss, but will report a sudden loss of smell as a result of an upper respiratory virus. In these cases, the virus interferes with the ability of the nose and/or sinuses to drain properly and sinusitis ensues. The specialized smell tissue at the top of the nose is not damaged, however. It is important to discern between viral damage and sinusitis as only the latter is treatable.
If an active process in the nose and/or sinuses is believed to be present and evaluation by an otorhinolaryngologist (ENT specialist) that includes nasopharyngoscopy should be considered. Thought should also be given to a CT (computerized tomography) scan of the sinuses. Once diagnosed, patients should be treated; normalization of smell function is possible with optimal management.