Patterns of Smell Dysfunction in Patient with Covid-19 Infection
Smell loss is one of the most common symptoms associated with Covid-19 infection. It can occur as the onset symptom early in the infectious process or as the only symptom of the infection. It can persist for five to seven days and then spontaneously disappear. It can also occur along with other common symptoms of the infection such as fever, chills, coryza, malaise and other systematic symptoms that commonly occur, and as these other symptoms remit the smell loss may also remit. These patterns are the most common manifestations of smell loss associated with Covid-19 infection.
However, in as many as 1/3 of patients with Covid-19 these symptoms of smell loss persist and are usually associated with loss of ability to recognize the taste of food. These symptoms may persist and reflect the major characteristic of smell loss following Covid-19.
Over time there are multiple specific patterns of smell dysfunction which may occur. One pattern is the specific persistence of smell loss which may vary to some extent over time but persists as a general loss. A second pattern is when the smell loss persists with it becoming associated with the onset of taste distortions in the mouth absent the taste of food or distortions in the nose in the absence of any odors. Taste and odors and may also develop a distorted, obnoxious quality. These can occur with the presence of the obnoxious taste in the mouth or smell in the nose, or it can also occur only with the presence of an external odor or a taste. These distortions may be present even though the loss of taste and smell may remit or may even disappear. A third pattern may occur with the persistence of these distorted tastes and smells in the absence of food or odors but with the onset of distorted taste and smell associated with the taste of food or smell of odors. These distortions may occur as the major sensory dysfunction associated with Covid-19 and may present in the absence of any other systemic symptoms such that they are the major sensory changes which persist with Covid-19 infection.
This complex series of events reflects the result of the Covid-19 virus attack on the receptor functions of the smell and taste systems. Their attack reflects that the so-called growth factors that maintain olfactory and taste receptors may be absent or decreased.
These results occur regardless of the variants of the virus which affect taste or smell function but its persistence is consistent with the inhibition of the growth or transcription factors which stimulate the stem cells in each sensory system.
See Henkin, Robert I. How Does COVID-19 Infection Affect Smell? JAMA Otolaryngology. January 2021.