Parosmia - Causes, Diagnosis, and Treatment

What Is Parosmia?

Parosmia is a qualitative olfactory disorder characterized by an abnormal perception of olfactory stimulus (smell). Sometimes the person with parosmia will find that the smell which is pleasant seems unpleasant for him or her, or the smell that he or she used to like now seems unpleasant. It could be due to parosmia. If a person has parosmia, then either the sense of smell seems to be altered or distorted, or completely lost. This parosmia can be temporary or permanent and will depend on the cause.

What Causes Parosmia?

Parosmia can occur when the neurons that detect the scent are damaged or are affected by any medical condition. These neurons are present in the lining of the nose and send signals to the brain, and the brain interprets the smell. The neurons may be damaged or affected due to viral infections or other medical conditions. When these neurons are damaged, it changes the way the brain interprets any smell.

These signals from these neurons are received in the olfactory bulbs present underneath in the front of the brain, and they interpret whether the smell is pleasing, enticing, appetizing, or foul. Any damage to these olfactory bulbs can also be the reason for parosmia.

The conditions that can cause parosmia are briefly discussed below:

• Bacterial or Viral Infection - One reason for parosmia is the damage to the olfactory neurons from a cold or a viral infection. Upper respiratory infections can cause damage to these olfactory neurons. These occur mostly in older patients as compared to younger patients with the same infection.

• Head Injury or Brain Trauma - Injury to the brain from trauma is linked to parosmia due to olfactory damage. The duration and severity of the parosmia depend on the injury. Parosmia from injury can also be due to damage to the olfactory nerve fibers at the cribriform plate (part of the skull). This can also be caused by seizures which will affect the brain.

• Chemical and Smoking - Parosmia can also be caused due to damage to the olfactory neuron from smoking. This can happen gradually. Likewise, exposure to chemical toxins can also cause damage and eventually result in parosmia.

• Side Effects from Cancer Treatment - Radiation and chemotherapy, which are done as a part of cancer treatment, have been reported to cause parosmia in many patients.

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• Neurologic Conditions - Conditions like Alzheimer’s and Parkinson's disease have been seen to affect the olfactory senses. One of the early arising symptoms of Alzheimer’s disease and Parkinson’s disease is parosmia. Other conditions like Lewy body dementia and Huntington’s disease can also cause this.

• Tumors - One of the rarest causes of parosmia is a tumor on the olfactory bulbs in the frontal cortex.

• Covid-19 Infection - Covid-19 infection is seen widely to cause anosmia (that is, loss of smell) in affected patients and is seen to revert back once the infection subsides. In some patients, it is seen to cause parosmia by affecting the olfactory system.

How Is Parosmia Diagnosed?

For parosmia, you may have to consult an otolaryngologist, also known as ENT (ear, nose, and throat) specialist.

• During the visit, certain things will be presented, and the patient has to describe the scent and rank them according to their quality.

• One of the common tests to diagnose parosmia involves a small booklet of “scratch and sniff” items that the patient needs to test and respond to the doctor.

• The doctor will ask for the family history of cancer and any neurologic conditions, history of any recent infections, lifestyle factors, and medicines that are taken.

If the doctor suspects that the cause could be due to cancer or any neurologic problem, they may suggest other investigations, which include:

• CT scan.

• Biopsy of the sinus.

• MRI scan.

What Are the Treatments for Parosmia?

The treatment for parosmia depends upon the severity and the cause of the parosmia. In most cases, the senses return back to normal once the causative factor is stopped or removed. In some cases, like in the case of tumors and nasal obstruction like nasal polyp is the reason for the parosmia, then surgery might be required to remove the causative factor.

Treatment for parosmia includes:

• Zinc.

• Vitamin A.

• Antibiotics in case of infections.

• Topical steroids and antihistamines have significantly improved parosmia cases associated with allergic and post-infective rhinosinusitis.

• Olfactory training.

There is no treatment for parosmia, which occurs as a result of viral infections like Covid-19 or head injury. The injured or damaged nerve fibers can grow back in your nose and nasal cavity, and the sense of smell will be fully or partially recovered.

What Are the Complications of Parosmia?

For healthy living, all the organs and senses should be functional in our bodies. If we have any health-related issue, it greatly affects the quality of our life. Smell plays an important part in life; like for enjoying food, the sense of smell plays a major role. It also plays an important role in professions like chefs, perfumers, and firefighters. In such people, parosmia may make it hard for them to do their job. Also, parosmia can have other effects and can lead to problems like:

• Loss of appetite.

• Weight loss.

• Depression.

Can One Recover From Parosmia?

Parosmia is not a permanent condition in most cases. If the parosmia is caused due to any damage to the nerve fibers, this can be recovered once the nerve fibers grow back. In the majority of cases, parosmia is caused due to viral infections, which are reverted back once the infection subsides. But in some patients, it may take a long time for the sense to recover to normal.

The recovery rate depends on the cause of the condition and also the treatment for the same. Also, it will depend upon the patient's factors, like age and pre-existing medical conditions.

Conclusion

Parosmia is a condition that affects the sense of smell. It could be caused by infection, brain trauma, smoking, chemical fumes, or medications. The recovery depends upon what causes parosmia. The condition is recovered once the triggering factor is removed. This condition greatly affects the quality of life. Consult a doctor when you start to experience any change in the way you sense smell. The prognosis is always good for this condition.