Anosmia or loss of smell: causes and symptoms of the disease

 A relatively common sensory disorder, anosmia affects 10 to 12% of the population.

A largely misunderstood and very often ignored disease which is characterized by a loss of smell and an alteration of taste sensations in the majority of cases.

What is anosmia? How to recognize it and what are its main causes? We take stock.

Anosmia: what is it?

Anosmia is the total or partial loss of the sense of smell. It is usually associated with a partial or total loss of taste, also called ageusia .

Anosmia is characterized by great difficulty in smelling an odor and in recognizing the aroma or flavor of food.

When anosmia results in a partial loss (decrease) of the sense of smell, it is called hyposmia .

Anosmia is usually bilateral but can sometimes involve only one nostril. When this is the case, it is called hemianosmia .

Anosmia is a pathology not to be confused with other smell disorders such as:

- cacosmia : constantly feeling a bad smell, whether real or not;

- parosmia : the deformation of certain smells.

Anosmia or loss of smell: what symptoms?

People with anosmia no longer smell odors and often complain of a loss of taste (ageusia).

In fact, people with the disease have great difficulty in distinguishing the aromas and flavors of food and therefore in appreciating food. They can recognize whether foods are sweet, salty, sour and bitter, but cannot tell the difference between specific flavors.

We then deduce that the ability to distinguish aromas and flavors depends on the sense of smell and not on the taste receptors of the tongue.

What are the causes of anosmia?

Anosmia can have several origins and the causes of anosmia are multiple.

Anosmia may be due to damage to the cells of the olfactory mucosa, the olfactory nerve or the olfactory nerve center where olfactory messages, i.e. smells, are processed.

Anosmia can be present from birth or acquired as a result of a pathology or behavior.

Congenital anosmia

When anosmia is present at birth, it is called congenital anosmia . However, few people are born without the sense of smell.

Congenital anosmia can be isolated or associated with a syndrome .

Isolated anosmia

Isolated anosmia is due to a malfunction in the development of the olfactory bulbs or an abnormality of the olfactory tissue. Isolated congenital anosmia is extremely rare.

Syndrome-associated anosmias

Anosmia associated with a syndrome, the best known is that of Kallmann . It is a genetic disease of embryonic development, characterized by damage to the olfactory bulbs due to hormonal insufficiency.

Acquired anosmia

You should know that when anosmia is an acquired disorder, due to an illness (sinusitis, cold, etc.), it is generally transient.

In the majority of cases, anosmia is due to an acquired disorder.

There are two types of anosmia:

• Anosmia of perception : we speak of anosmia of perception when there is a dysfunction in the perception of olfactory information (odors).  The sensory organs are affected, in other words, the olfactory nerves are impaired.
• Transmission anosmia : we speak of transmission anosmia when it comes to disorders of the transmission of olfactory information (odors) . The odorous molecules do not reach the sensory cells because of a lack of permeability of the nasal cavities. Transmission anosmia is due to obstruction of the nasal passages and cavities.

Perceptual impairment

Perceptual impairment may be due to:

• certain drug treatments such as anti-cancer treatments, morphine, etc. ;
• radiotherapy against cancer can lead to anosmia or loss of taste (ageusia) which can last for months and even become permanent;
• a surgical intervention ;
• head trauma due to a traffic or other accident;
• certain infections, in particular those of the upper respiratory tract, caused by the influenza virus (flu), responsible for almost a quarter of hyposmia or anosmia;
• certain infections caused by the herpes simplex virus;
• viral hepatitis, inflammation of the liver caused by a virus;
• poisoning due to the inhalation of harmful substances or industrial pollutants in the workplace, for example;
• neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease or epilepsy;
• other degenerative brain diseases such as multiple sclerosis;
• a tumor, often benign, which develops in the meninges,
• an olfactory meningioma;
• age: as we get older, the olfactory faculties weaken. Indeed, the loss of olfactory receptors leads to a decrease in the ability to smell odors in the elderly from the age of 60. After 70 years, changes in the sense of smell become significant.

Disorders due to impaired transmission

Anosmia corresponds to a disorder in the transmission of odors when the odorous molecules do not reach the sensory cells of the system.

Anosmia may be related to an anatomical abnormality characterized by:

• poor quality of mucus or olfactory mucosa;
• Naso-sinus polyposis (chronic sinusitis): a disease of the nose and sinuses which is characterized by the formation of edema and polyps in the mucous membranes blocking the transmission of odors. This disease affects 5% of the population;
• the presence of a foreign body in the nose, a tumor for example, thus blocking the nose and altering the sense of smell;
• an underlying illness such as a cold;
• an underlying disease such as rhinitis : an inflammation of the mucous membrane of the nasal cavities which can have several origins, in particular an allergic origin. Seasonal allergies such as allergic rhinitis can indeed impair the sense of smell;
• an underlying disease such as chronic sinusitis  : inflammation of the mucous membranes of the sinuses;
• a deviation of the nasal septum.

Finally, it happens that the anosmia is idiopathic, that is to say that it has no identified cause. The loss of smell occurs without explanation.