Coronavirus (Covid-19) disease is a highly contagious infectious disease caused by the SARS-CoV-2 virus. Basically, it can be transmitted from animal to human and from person to person via droplets. The incubation period of the disease is about 1-14 days (average 5.2 days). Coronavirus is highly resistant to external environments due to it being an enveloped virus, and it has been revealed in various studies that it can live on inanimate surfaces for up to 14-21 days. The disease started in Wuhan, China at the end of December 2019, and spread to all continents in a short time and was declared as a pandemic by the World Health Organization (WHO) in March 2020. As of May 2020, nearly 4 million cases and nearly 300,000 deaths have been reported[18–20].
COVID-19 disease affects the respiratory epithelium. The disease starts like a cold and can turn into pneumonia in a short time. If the disease progresses further, it progresses to Acute Respiratory Distress Syndrome (ARDS) and leads to mortality. It is believed that viral load is important in worsening the illness. The viral load was reported to be highest in the lower respiratory tract – in the bronchoalveolar fluid (93%), secondarily in the upper respiratory tract, nasopharynx (60%), and thirdly in the pharynx (30%). The disease is diagnosed by bronchoalveolar lavage fluid, nasopharyngeal or swabs from the oropharynx, via an RT-PCR test. In addition, it can be diagnosed as a rapid antigen test with serological methods. The disease has been reported to be more severe in males, smokers, elderly and those with additional diseases[21]. In our study, the relationship of the disease to gender was not detected. Elderly and additional diseases were influential in mortality (p <0.05, p = 0.046, respectively). No relation was found between smoking and the degree of smell disorder. (p> 0.05)
Imaging in COVID-19 pneumonia is much more important than many viral diseases. There are even authors who report that the disease is as important as the PCR test. The classic finding in thorax CTs that are routinely seen in patients is the “ground glass view”[22, 23]. COVID-19 recently reported cases with pulmonary imaging, Abdomen CT and Brain CT. Encephalitis has been reported in the brain as in some viral infections. A possible way for this to occur is via nasopharynx, sphenoid sinus, frontal sinus and cerebrospinal fluid[24].
Post-viral odor loss has been identified in many viral diseases, primarily Influenza and Rhinoviruses[12–14]. Patients with sudden olfactory loss were even reported in the MERS- CoV outbreak in 2012[25]. In the COVID -19 pandemic, which started in China on December 2019, patients with sudden olfactory loss have been reported in countries such as China, Italy, Spain, Singapor and USA where pandemics are frequently seen. The rate of 5% was seen in a study in China and The American Academy of Otolaryngology-Head and Neck Surgery" in the study were reported as striking as the first symptom in 73% Health 26.6% patients.[25– 28]
It is obvious that the disease causes much more olfactory disorders than other viral infections. In this, the direct damage to the olfactory epithelium of the virus or the neural retrograde pathway can have an effect on the olfactory region containing the odor receptors in the region. From a study, the nucleic acid of the virus has been detected in both the brain tissue and the cerebrospinal fluid (CSF) [29, 30]. In the spread of the virus in the body, into many tissues and nervous system of the body, the angiotensin converting enzyme 2 (ACE 2) and transmembrane serine protease 2 (TMPRSS2) proteins plays a role. However, in a new study, it was shown that ACE 2 and TMPRSS2 proteins were not found in the olfactory region in humans. Therefore, there is no role of these proteins in olfactory damage. On the contrary, damage to basal cells was detected. Therefore, the possible mechanism in olfactory disorder appears to be the damage of these cells. Therefore, the biochemical reaction in the formation of odor cannot take place[31–34]. In our study, when we evaluated Paranasal CTs taken from patients with odor loss, pathological findings were observed in 2 patients' CT and were statistically significant (p <0.05).
Since odor disorder is a subjective concept, objective tests were needed in its diagnosis. There are two types of odor tests, psychophysical and electrophysiological tests. In the diagnosis of smell disorder, smell tests are used in practice. These tests are carried out in two stages as odor threshold tests and odor odorant tests. In the threshold determination test, a scent bottle containing fragrances such as phenyl ethyl alcohol (PEA) or butyl alcohol (butanol) 4% and another bottle containing only water are presented to the patient. Odor detection tests are quantitative tests. Patients are asked to identify fragrances above the threshold. The most used of these are The University of Pennsylvania Smell Identification Test (UPSIT), Sniffin' Sticks, Connecticut odor detection test-CCCRC, OSIT-J (Odor Stick Identification Test for Japanese, Daiichi Yakuhin, Co., Tokyo, Japan), B-SIT (the Brief Smell Identification Test) and the Crosscultural smell identification test (CC-SIT). The most widely used of these tests is the UPSIT test[10, 15, 35]. These tests can also be used in the diagnosis of olfactory disorders in COVID-19 . In a study, the UPSIT test was used in patients with COVID-19 smell disorder, and according to this test, most patients were found to have a loss of smell ranging from mild microsmia to anosmia. The test scores were not related to age, degree of disease, nor additional diseases[10]. In another study, a smell and taste change survey was conducted on social media, and a significant result for COVID-19 was found in those with this symptom[35]. In our study, the CCCRC test, which is more suitable for Turkish society, was used. A correlation was found between both clinical and PNS CT finding on the positivity of the CCCRC score. As patients' illness worsened, an increase in olfactory loss was observed (p <0.05). A statistically significant relationship was found between the CCCRC score and PNS CT findings (p = 0.012).
In literature, single Paranasal imaging in patients with COVID-19 with olfactor impairment has been reported in a single patient in the USA. A thickening and drainage disorder in the olfactory region was reported in this patient in coronal sections. It is estimated that the olfactory bulb is retained through the cribriform plate depending on the involvement of the respiratory epithelium in patients with COVID-19[11]. In a study related to post-infectious olfactor loss, the infection-related olfactory bulb volume was shown to decrease38. In our study, in the majority of patients with COVID-19 with olfactory disorders, obstructive thickening and loss of aeration were observed, especially in the Paranasal Sinus CT, which disrupted the olfactory region drainage. Thus, the cause of olfactory loss in these patients was confirmed by imaging. In addition, a significant relationship was found between the degree of odor disorder and the positivity of CT findings.
Since there were 40 patients in the study, the study needs to be done in larger series and in multiple centers.