Postviral olfactory loss

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Incidence

A viral upper respiratory infection (URI) is one of the most commonly identified causes of persistent olfactory dysfunction. Data from the University of Cincinnati Taste and Smell Center reported a viral etiology in 78 of 354 patients presenting with a smell loss, or 22% [1]. Other centers have reported similar experiences. The Connecticut Chemosensory Clinical Research Center described 82 patients of 441, or 18.6%, presenting with an olfactory loss following a viral URI [2]. Of 750 patients

Pathophysiology

Although it is unknown which virus is most often associated with olfactory loss, viruses can invade the central nervous system through the olfactory neuroepithelium and olfactory pathways [9]. Damage may occur at the level of the epithelium and receptor cells, or in central processing pathways such as the olfactory bulb. [6] Several animal studies have demonstrated damage to central olfactory pathways and other areas of the brain after intranasal inoculation of different viruses [10], [11].

Diagnosis

There is no definitive test that will identify clearly an olfactory loss as being postviral. The diagnosis is made when a loss immediately follows a URI, in the absence of any other apparent etiology. Patients will describe a persisting olfactory deficit after resolution of cold or flu symptoms, often describing such infections as having been particularly severe. Patients usually will remember such an episode, even though they may not present for months or years afterward. If they do not

Therapy and prognosis

Olfactory neurons present receptor nerve endings that are exposed directly to the external environment, making them unique and vulnerable to injury. Perhaps this is why these bipolar neurons are the only neurons in the central nervous system that can regenerate [22]. At least in theory, therefore, the sense of smell should be able to recover following any number of environmental insults. In reality, this does not occur consistently.

Preliminary observational studies of postviral olfactory loss

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