May 29, 2023

Table of contents

What is anosmia?

Anosmia, which can be simply explained as the inability to smell any odor that can be smelled in any environment, is also known as smell blindness. Some people cannot smell anything at all, while others cannot smell light or strong odors.

After the Covid-19 pandemic, it became clear that Anosmia also causes other disorders. These disorders include perceiving some odors differently than they are. This condition is called parosmia. There are also cases where some odors are perceived as rotten. This condition is called cacosmia.

Symptoms of anosmia

The most characteristic symptom of anosmia is the inability to smell odors in the environment. Anosmia is usually manifested by the inability to smell the food consumed. However, in order for anosmia to be diagnosed, pungent odors such as cologne and perfume, which are part of daily life, should not be smelled. The sense of smell may disappear bilaterally or unilaterally. However, there is no way for people with Anosmia to understand this.

Diagnostic criteria for anosmia

Patients’ complaints are the priority for the diagnosis of anosmia. For this reason, patients presenting to the outpatient clinic with the complaint of not being able to smell should first be differentially diagnosed. Because Anosmia can be a symptom of other diseases or it can be a disease in itself.

In order to detect the inability to smell, some chemicals are diluted with a certain amount of water and then the patients are made to smell this solution. These tests include olfactometry, in which odorous gases are sniffed, and butanol threshold tests.

However, when it comes to anosmia, the important thing is to identify the cause of anosmia. For this reason, patients undergo various tests and imaging methods:

  • MRI and CT scans of the brain investigate whether there is a condition in the brain that causes the conduction blockade of odor.
  • Sinus tomography
  • Endoscopic examination

Treatment of anosmia

In the treatment of anosmia, the main cause of anosmia is first identified. This underlying cause needs to be treated. If there are nasal polyps in the nose, the polyps must be removed to restore the sense of smell. In the case of Anosmia due to allergy, controlling the allergy with various medical drugs can restore the sense of smell. In addition, in patients with nasal curvature, surgical operation is required to correct this defect.

In some patients, the olfactory nerves may be damaged by trauma, infection or sinusitis. In these patients, it is not possible to treat Anosmia because the nerves cannot be restored.

Causes of Anosmia

Before moving on to the causes of anosmia, it is necessary to talk about how odor is perceived in order to fully understand it. Odor molecules bind to air molecules. These molecules in the air are drawn into the nose when inhaled. In the upper part of the nose, there are olfactory receptors involved in the perception of odor. Odor molecules coming to the odor receptors covering 1/3 of this region are decomposed by enzymatic reactions. The nerve endings then detect this smell and are directed to the smell center in the brain. The olfactory center determines what the smell belongs to.

Any problems at these stages cause the odor to be inaccessible. Problems are in two main groups. The first is that the transmission of odor molecules is blocked for some reason. In this so-called sensorineural type of olfactory disorder, although odor molecules are decoded in the nerves, the necessary signals cannot be transmitted to the brain due to various problems. Among the factors that cause this are the following:

  • The most common cause of sensorineural olfactory impairment is brain aneurysm.
  • Brain surgery
  • Parkinson
  • Epilepsy
  • Hormonal diseases
  • Alzheimer’s disease
  • Skull base fractures
  • Brain tumors

In addition, in conduction-type Anosmia, odor molecules cannot be transmitted to the olfactory nerves in the nose for any reason. Among the reasons why odor molecules cannot reach the nerves are the following:

  • Nasal polyps swell and block the nose
  • Severe nasal curvature
  • Nasal obstruction due to upper respiratory tract infections
  • Corona virus Some viruses can cause sensorineural odor loss as well as conductive odor loss.
  • Hookah, cigarette or drug use

Other odor disorders

There are many other olfactory disorders besides anosmia. Hyposmia or microosmia is defined as a reduced ability to smell, while hyperosmia is defined as hypersensitivity to odors. There is also an olfactory disorder called dysosmia, which is the perception of odors as bad or distorted. The condition called cacosmia and parosmia is the deterioration of odor quality. In some people, although there is no odor, the condition of smell is called pantosmia. The age-related decline in the sense of smell is called presbycusis, while olfactory agnosia is the absence of olfactory processing even though all functions are normal.

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