Anosmia - Causes, Symptoms, Diagnosis, and Management

Introduction:

Anosmia is a partial or complete loss of smell. A person with anosmia loses the ability to sense odors. Loss of smell is a warning sign of the presence of underlying health issues. Any infections irritating the nasal mucosa or causing nasal obstruction can result in loss of smell. Cold or flu and sinus (hollow space within the skull bone connecting to nose) infections can lead to temporary loss of smell which gets subsided as the infection is cured. Olfactory nerves function to perceive smell sensation in the nose; any damage to the olfactory nerves (first cranial nerve) due to trauma during surgery or by the presence of neurological (nerve) disorders can result in loss of smell which needs medical attention.

What Is the Prevalence of Anosmia?

• The prevalence of anosmia is around two to three percent of the general population.

• The prevalence of anosmia in patients with corona infections is about 40 to 45 % worldwide.

What Is the Incidence of Anosmia?

• Anosmia mostly affects people in the age group of 60 to 80 years old.

• Anosmia is more common in males than females.

What Are the Causes of Anosmia?

Loss of smell is associated with various factors like:

• Head injuries.

• Nasal fractures.

• Sinusitis (infection of the spaces within the skull bone connected with the nasal cavity).

• Cold or flu.

• Viral infections like coronavirus, influenza, or hepatitis infections.

• Nerve disorders causing injury to olfactory nerves (first cranial nerve) result in loss of smell, like Parkinson's disease or multiple sclerosis.

• Nasal deformity like deviated nasal septum.

• Cancerous or non-cancerous tumors like nasal polyps cause nasal obstruction.

• Addiction to inhaling cocaine.

• Trauma to the nose during surgery causes nerve damage.

• Nutritional deficiency like vitamin B12 deficiency.

• Allergic rhinitis (infection due to allergies to the nose).

• Chemical exposure (exposure to insecticides).

• After undergoing radiotherapy.

• Smoking.

• Aging (with age, the number of cells in the olfactory bulb is reduced).

• Medications like intranasal zinc.

What Are the Symptoms of Anosmia?

• Inability to identify any smell.

• People may have altered eating habits due to loss of smell.

• Weight imbalance (weight gain or loss) due to reduced eating or overeating because of the inability to smell.

What Is the Mechanism of Smell Work?

Many of us are curious to know how our noses can perceive so many different odors.

There are thousands of different odor-binding proteins present on the olfactory (first cranial nerve) receptor cells or neurons (receptors present in the nose). Each neuron or receptor expresses only one binding protein.

How Can We Diagnose Anosmia?

Loss of smell can be diagnosed by an ENT (ear, nose, and throat) specialist by :

• History and Clinical Examination: History of any recent trauma, previous surgeries, and radiotherapy should be recorded. A clinical examination of the nose should be done to identify any soft tissue growth causing nasal obstruction.

• Computed Tomography (CT) Scans: These scans help to diagnose any soft tissue growth present in the nasal cavity, like nasal polyps resulting in nasal obstruction.

• Magnetic Resonance Imaging (MRI): These scans are done to check for any cancerous or non-cancerous tumor compressing the nerves and rule out any damage to the olfactory bulbs and olfactory tract.

• San Diego Odor Identification Test (SDOI): It is the most frequently used test currently. In this test, eight everyday food items are kept in an opaque plastic jar for sniffing, and patients are asked to identify them.

• Scratch and Sniff Test: In this test, patients are given a paper booklet that contains tiny beads filled with different odors on each page. The patient is asked to scratch and then sniff to identify the correct odor.

What Is the Treatment for Anosmia?

Treatment modalities for anosmia depend on the cause:

• Antibiotics: Antibiotics like Ampicillin should be started to treat the underlying bacterial infections as prescribed by the doctor.

• Intranasal Steroid Sprays: Glucocorticoids intranasal spray is used for the presence of any swelling and obstruction in the nasal cavity.

• Antihistamines: Antihistamine drugs should be taken to treat allergic rhinitis (nasal mucosa swelling due to allergies).

• Surgery: Surgery is advised to treat nasal obstruction, like surgical removal of nasal polyps done by an ENT (ear, nose, and throat) specialist.

• Nutritional Supplements: Nutritional deficiencies like vitamin B12 deficiencies should be ruled out, and nutritional supplements should be started for the same.

• Treatment of Underlying Nerve Disorders: Nerve disorders like multiple sclerosis and Parkinson's disease should be reported to the doctor, and treatment should be started.

How Can We Prevent Anosmia?

• Avoid smoking.

• Rehabilitation for reducing or quitting cocaine addiction.

• Treatment of underlying disorders like nasal polyps, viral infections, or nasal tumors under a doctor's supervision.

• Avoid exposure to industrial chemicals and pesticides for a longer duration in closed spaces.

• Report to the doctor if any nasal infections like allergic rhinitis or sinusitis are there and start the medications for the same as prescribed by the doctor.

Conclusion:

Loss of smell sensation disturbs the quality of life of every person. Most of the time, the anosmia gets reversed after treating the underlying symptoms, but in some cases, anosmia is a warning sign of the presence of serious health issues. Loss of smell for a longer duration should be reported to the doctor immediately for early diagnosis and management of the cause that leads to anosmia. Anosmia due to damage to the olfactory (first cranial nerve) neurons cannot be cured as these neurons do not regenerate, and none of the treatment modalities has yet been introduced that can regenerate the damaged neurons. Further research and studies are ongoing in this area to promote the regeneration of the sensory neurons.