Smell (Olfactory) Disorders and Covid-19

Smell Disorders

Smell disorders can be due to many different causes. Inability to smell "Anosmia", decrease in smell "Hyposmia", hypersensitivity to odors "Hyperosmia", misperception of odors "Dizosmia", perception of odors as bad odor "Cacosmia", perceiving the opposite of odors "Parosmia", perception of code even though there is no odor in the environment " Fantosmia is called "Heterosmia", the difficulty in distinguishing different odors from each other. The absence of sense of smell from birth is called congenital anosmia.

It is not easy to measure the amount and find the cause of the problem in odor problems.

In the links below, you can find information about the causes, diagnosis and treatment of disturbances in the sense of smell.

Causes of Smell Disorders

Depending on all inflammatory diseases affecting the olfactory area (such as sinusitis, flu, cold ...) and all causes affecting the air intake to this area (such as mass, septum deviation, turbinate hypertrophy, polyps, nasal enlargement, allergic rhinitis, etc.) There may be a decrease in sense of smell. Apart from these, in events affecting the neural pathways in the head and between the nose and skull (increased intracranial pressure, head trauma, meningitis, head trauma, neurosyphilis, temporal lobe tumors, multiple sclerosis ...), diseases in which the cilia in the nose are affected (Kartagener syndrome, Afzelius syndrome, Siewert syndrome ...), various drug uses (such as chronic steroid use, various antibiotics, antithyroid drugs ...), chemical gases (sulfuric acid, benzene, butyl acetate, formaldehyde, hydrogen sulfide, nitrous gases ... ) in case of exposure, after nasal surgery, after anesthesia, in psychiatric diseases such as depression, hyphysectomy surgery, after hemodialysis, in Sjogren's Syndrome, endocrine disorders (such as diabetes mellitus, hyperthyroidism or hyprothyroidism, Addison's Disease ...) and Methotrexate. After the use of chemotherapy drugs, disorders related to smell can be seen.

During pregnancy and menstruation, problems with smell can be seen due to hormonal effects. Prolonged smoking may cause a decrease in smell due to the negative effect on the epithelium in the olfactory area.

How Are Smell Disorders Diagnosed?

Tests that can objectively measure the amount of disorders related to smell are insufficient. Almost all odor tests are subjective.

For the diagnosis of smell disorder, attention is paid to the following:

In the patient's history:

- The starting time of the olfactory disorder

- Risk factors such as trauma, upper respiratory tract infection and drug use that may cause smell disorder are questioned.

In the examination of the patient:

- Cartilage curvature (septum deviation), concha hypertrophy, nasal polyp, allergic rhinitis, mass and tumoral lesions that may cause nasal obstruction are investigated.

As an imaging method that can aid diagnosis:

- Computed Tomography

- MRI may be requested

Apart from these, the following odor tests can be applied to each nostril:

- Dilution tests

- Olfactory Spectrogram

- Butanol Threshold Test

- Odor discrimination test

- Odor detection test

- Smell recognition test

- Fragrance identification test

- Electro-olfactography

- Evoked olfactory potentials (In this test, the brainstem potentials that emerge by sniffing the fragrant substance are measured in electroencephalography. It is advocated that it can be used as an "objective test" in the investigation of odor disorder)

Biopsy of the olfactory area (alfactor area) mucosa in the nose is rarely required.

COVID-19 and Olfactory Dysfunction

According to the World Health Organization (WHO), coronaviruses; It is a family of viruses that cause diseases such as the common cold, severe acute respiratory syndrome (SARS), and Middle East respiratory syndrome (MERS). Countries around the world continue their fight against the new coronavirus intensely. One of the signs of infection detected in this process is the loss of taste and smell. It is stated that the reason for these sensory losses is the disturbance in the stimulation of the vessels that feed the taste and smell nerves. The loss of these senses that you need to perceive the environment you are in and the food you consume significantly affects your daily life.

Since the beginning of the coronavirus epidemic, it has been revealed that many people living with the infection have lost their sense of smell and taste. However, the problem is not limited to seriously ill patients. It appears to be a common and even "cardinal" symptom among people with milder coronavirus infections. Cardinal symptoms are the key symptoms by which the diagnosis is made.

In a study of European patients with mild to moderate coronavirus infection, 86% of patients reported problems with their sense of smell. In addition, there have been changes in the sense of taste. Colds and respiratory viruses can sometimes trigger a loss of smell. It is known that the loss of smell, called anosmia, causes a decrease in the sense of taste. However, it is also possible for the coronavirus to have a direct effect on the sense of taste. In some patients, even after infection; They can emphasize that they constantly smell bad fish and burnt bread. Some patients may say that coffee smells like exhaust and toothpaste smells like gasoline ...

How Does Covid-19 Cause Smell Disorder?

In experimental studies, it has been shown that the virus reaches the olfactory center in the brain via the olfactory nerve fibers after it is transmitted into the nose. Some of the viruses taken through the nose reach the lungs and cause infection here. It is thought that some of them proliferate in the epithelium in the olfactory area located on the ceiling of the nasal cavity and reach the brain through the olfactory nerve and cause smell disorders, and taste disturbance develops as a result of similar effects on the nerves that transmit the sense of taste to the brain.

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a new type of coronavirus agent, is a common problem all over the world due to the emergence of severe life-threatening infections, different clinical pictures and health problems. The most common symptoms of COVID-19 are fever, sore throat, and shortness of breath. According to anecdotal reports from healthcare professionals, it was suggested that the virus could reach the brain and cause anosmia, hyposmia (decreased sense of smell), hypogeusia (extremely weak sense of taste). After SARS-CoV-2 enters the central nervous system (CNS), it can inactively exit the tissues or cause neuroinflammation. Here, we aim to discuss chronic infection of the olfactory bulb region of the brain by SARS-CoV-2 and how this may affect nearby neurons in the host. We review in more detail the possible cellular mechanism and activation of the microglia 1 phenotype, which likely leads to various neurodegenerative disorders. As a result, SARS-CoV-2 can possibly infect the olfactory bulbus neuron that irritates the nasal epithelium that accesses the CNS and can cause future neurodegenerative diseases.

In most patients, the situation is not permanent, but there are not enough clinical studies on the subject!

In a study, it was found that 88 percent of the patients who reported smell and taste disorders improved within 4 weeks. It was observed that the situation did not change and the disorder continued in 12 percent. It has been reported that most smell and taste disorders are not permanent. However, this period is short to make a clear assessment of whether the disorder is permanent or not. More clear information can be obtained with longer term studies.

It can also be seen in other viral infections that affect the respiratory tract of smell and taste disorders!

In patients with coronavirus infection; In addition to the main symptoms such as high fever, dry cough, and shortness of breath, taste and smell problems can be observed. However, taste and smell disorders are not only symptoms of coronavirus, but can also be seen in colds and many other types of diseases caused by other factors. Other symptoms seen in the individual are decisive in determining the reason for the problem in question. Causes of taste and smell disorders include old age, cold and flu infections, allergies, nasal polyps, psychiatric diseases, dry mouth and tooth decay, exposure to chemicals, smoking and drug abuse, use of various medications, facial paralysis, concussion and head. traumas, multiple sclerosis, Alzheimer's, Parkinson's and dementia, skull base tumors, vitamin and mineral deficiencies, some diseases related to the salivary glands, sinusitis. Similar link >> Anosmia, Hyposmia and Dysgeusia Can Be a Sign of Coronavirus Infection!

Treatment of Smell Disorders 

The treatment of olfactory disorders is based on the underlying cause. It is very important that upper respiratory tract infections (sinusitis, flu infection ...), which are the most common causes of olfactory disorder, are treated quickly, and the nasal interior is washed with saline water (sinus rhinse, sea water sprays ...) to remove harmful contents from the smell area.

There is a good comprehensive study on the subject published in 2009. In this study conducted in Korea, in patients with decreased sense of smell after viral infection, when Ginkgo biloba treatment was given with intranasal cortisone spray (Mometasone Nasal Spray) and oral cortisone treatment, especially in patients who received Ginkgo biloba treatment within the first 6 months, the sense of smell could return to normal emphasized. It was emphasized that there is nerve degeneration in the olfactory nerves and early intervention is very important, and the effect of medical treatment may be limited after 6 months. You can read a summary article about this study:

Study Examines Treatment For Olfactory Loss After Viral Infection

Accordingly, this information may be important in patients whose smell disturbance does not disappear after sinusitis treatment, although nasal congestion and sinusitis symptoms disappear. 

Source links >> Smell (Olfactory) Disorders—Anosmia, Phantosmia & Others ... / Smell disorders: When your sense of smell goes astray ... / Smell Disorders: Get Facts on Causes and Symptoms / Smell and Taste Disorders: A Primary Care Approach ... - AAFP / COVID-19 and olfactory dysfunction: A possible associative approach towards neurodegenerative diseases

Murat Enoz, MD, Otorhinolaryngology, Head and Neck Surgeon - ENT Doctor in Istanbul

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