In most cases (about 80%), COVID-19 can be mild or asymptomatic [1]. At the same time, patients often have a violation of the sense of smell and perception of tastes [2]. To date, a large number of publications have accumulated that specifically study the issues of loss of smell, the duration of its manifestation, the nature of recovery and methods of treating this problem. At the request of RBC Style, otorhinolaryngologist Oleg Abramov made a brief overview of the current data on this topic.
Oleg Abramov - otorhinolaryngologist, head of the department of operative otorhinolaryngology at GMS Hospital.
Loss of smell and ENT symptoms in COVID-19
Smell impairment after a viral infection is not uncommon in ENT practice, it occurs on average in 11% of patients. In some situations, it lasts a long time and in 22-26% of cases it becomes a reason to see a doctor [3, 4]
In addition to coronavirus, impaired sense of smell is caused by rhinoviruses, parainfluenza viruses and the Epstein-Barr virus [5].
Types of olfactory disorders:
- anosmia - complete loss of odors;
- hyposmia - partial loss of odors;
- parosmia - a change in the perception of odors;
- phantosmia - the perception of various odors in their absence;
- acosmia - a perverse perception of odors.
Based on scientific research data, it can be argued that a violation of the sense of smell in viral infections can occur in two ways.
Why is the sense of smell impaired in viral infections
- The first mechanism: damage to the cells surrounding (supporting) the olfactory epithelium, or damage to the olfactory neurons themselves in the nasal cavity. In this case, a deeper penetration of viruses along the nerve fibers of the olfactory pathway up to the cerebral cortex can also be observed.
- The second mechanism: against the background of a viral infection, edema of the mucous membrane occurs, as a result of which the normal functioning of the olfactory zone is disrupted.
The mechanism of impairment of smell in COVID-19 is not fully understood, the opinions of specialists were divided. The fact is that the penetration of the SARS-Cov-2 virus requires the presence of a certain protein - ACE-2, which, in particular, is actively secreted on the surface of the epithelium of the nasal cavity, and the supporting cells of the olfactory zone. The olfactory neurons themselves do not synthesize this protein. However, it is possible that the virus can migrate from these cells directly to the olfactory neurons, destroying them and penetrating into the deeper parts of the olfactory tract in the brain [6].
Research on olfactory disorders in COVID-19
The first data on impaired sense of smell began to appear in the spring of 2020. Various types of olfactory disorders were observed in 56–85% of patients. The most common was anosmia (about 70% of cases), followed by hyposmia - about 20% of cases [7]. Other types of olfactory disorders such as parosmia and acosmia were much less common.
In September 2020, a large study was published, the results of which showed that, among 3739 patients interviewed, a violation of the sense of smell was noted on average in 61% [8].
The timing of the onset of the olfactory disorder varies from patient to patient. A small proportion (11–26% of cases) notice this sign before the onset of any symptoms, but most often, a violation of the sense of smell occurs during (52%) or after the onset of symptoms (26%) [9]. The same work notes that in 45% of cases, a violation of the sense of smell was the only symptom of the disease. Odor problems are most commonly reported in patients with chronic nasal diseases, in smokers, and in women.
There is also a violation of taste perception. It is believed that the mechanism of taste disorder is of a secondary nature and occurs without affecting the taste buds and nerve endings in the thickness of the tongue - troubles are associated with damage to the olfactory zone in the nasal cavity and the inability to catch odors while eating [10]. However, in about 11% of cases, COVID-19 taste disorder can occur without loss of smell.
Smell recovery times in coronavirus patients
The timing of the restoration of the sense of smell is of the greatest interest today. What if after the illness the odors have not recovered or have recovered, but not completely? It is encouraging that, regardless of the type of olfactory disorder, in most cases (72–85%), recovery or significant improvement occurs, according to various sources, within 8–14 days after the onset of symptoms [11]. This reflects the course of the disease and the so-called viral load, which prevails in the nasal cavity and nasopharynx.
Together with a decrease in viral presence and recovery, most patients recover or significantly improve their sense of smell. However, a considerable part of patients (25–40%), who have a violation of the sense of smell, notes the persistence of this problem for two months [12].
Methods for treating olfactory disorders and their effectiveness
Given that the nature of the impairment of smell in COVID-19 has not yet been fully understood, various treatments have been tried in the studies. Of course, they differed little from the previously used methods for other viral infections, which are accompanied by a violation of the sense of smell.
Methods for treating olfactory disorders
- rinsing the nose with saline solutions;
- the use of hormone-based sprays to relieve inflammation and edema (strictly as prescribed by the doctor);
- olfactory training with essential oils.
It should be noted that scientists have not been able to establish a relationship between the use of these funds and the restoration of the sense of smell, that is, the effectiveness of these methods of treatment for impaired sense of smell in COVID-19 has not been proven [13]. Olfactory training with essential oils can be recommended for those whose sense of smell has partially recovered, but not in the case when the perception of smells is perverted or other disorders have occurred. The evidence base for the effectiveness of olfactory training in olfactory disorders after Covid-19 is weak.
Smell impairment and quality of life
Of course, the loss of function of any of the senses is a significant problem, in some situations equated to disability. To assess the degree of impairment of smell and the impact of this problem on the quality of life, special questionnaires were developed. It has been found that some patients become more irritable, their level of anxiety increases, appetite may decrease, social withdrawal develops, and there is also a risk of losing the sensation of dangerous odors, such as gas leaks [14]. All this undoubtedly creates the need to address these problems.
Prospects for the restoration of the sense of smell with its persistent loss
Research data have shown that the regeneration of the olfactory epithelium after viral infections occurs through neural stem cells, from which both the olfactory epithelium and the cells that support the olfactory neurons are regenerated [15]. With a chronic inflammatory process in the nasal cavity, this regenerative process is disrupted. Perhaps in the future, drugs will be developed to stimulate the regenerative process or protocols for transplanting stem cells responsible for the regeneration of olfactory neurons into a special zone in the nasal cavity will be created. One way or another, we can only believe that these studies will be initiated by analogy with stem cell transplantation for other pathologies in the human body.
How the loss of smell is experienced by people whose work is related to tastes and smells.