Parosmia and Phantosmia - The Curious Case of Smells

Introduction

Parosmia and phantosmia are regarded as qualitative olfactory disorders that can significantly influence a person’s life quality. In parosmia, the previously enjoyable odors would currently seem to be foul-smelling to a person. It usually occurs as a result of viral infection. In phantosmia, a person could smell something that is actually not present in the environment. These smells could usually be unpleasant, like metallic, chemical, or burnt toast kind of smells. The probable reasons for phantosmia could range from nasal polyps to a stroke. Phantosmia is also referred to as an olfactory hallucination or a phantom smell.

How Does Parosmia Differ From Phantosmia?

In phantosmia, one detects a ‘phantom’ scent, but no such odor actually exists. In parosmia, a person can detect a particular smell, but it is detected incorrectly. For example, the odor of freshly baked bread is usually pleasant, but to a person with parosmia, this might smell rotten and overpowering. Parosmia can occur due to a variety of reasons. In severe cases, parosmia can make one feel physically ill when the brain identifies overpowering, unpleasant odors.

What Are the Causes of Parosmia?

Damage to the olfactory senses or odor-detecting neurons due to viral infection or other health issues can cause parosmia. These neurons are present in the nose and send signals to the brain on how to interpret the chemical information that constitutes a particular smell. Any damage to these neurons affects how these signals are interpreted. Some of the common causes of parosmia are as follows:

• Brain Trauma: Trauma to the brain can damage the olfactory (related to the sense of smell) nerve fibers that are located at the cribriform plate. Damage due to seizure can also cause brain trauma which could result in parosmia.

• Infections: Infections in the upper respiratory tract can affect the olfactory neurons, which is more prevalent in older adults.

• Smoking and Chemical Exposure: The olfactory system could be affected by cigarette toxins and chemicals. Even increased exposure to air pollution and chemicals could also cause parosmia.

• Cancer Treatment: Radiation and chemotherapy could also result in parosmia. A study conducted in 2006 showed that about 86 percent of patients undergoing cancer treatment experienced changes in smell and taste during the course of the treatment. Due to this, weight loss and malnutrition were noticed in these patients as a consequence of food aversions linked to parosmia.

• Neurological Conditions: The first and major symptom of Alzheimer’s disease (a gradually progressive disease that impairs memory and other vital mental functions) and Parkinson’s disease (a disorder that involves the central nervous system and affects movement) is parosmia.

• Tumors: It is uncommon for a tumor to cause parosmia, but tumors in the sinus cavities, frontal cortex, and the olfactory bulbs can alter the sense of smell. Mostly, individuals who have tumors experience phantosmia rather than parosmia.

• COVID-19 Infection: During the COVID-19 pandemic, a majority of individuals experienced loss of smell (anosmia). But, there are possibilities that one could experience parosmia following the COVID-19 infection since it is a viral infection and the COVID-19 virus could cause alterations to the olfactory system. Some healthcare professionals regard parosmia following COVID-19 to be a sign of recovery. The link between parosmia and COVID-19 infection is still under research, and further studies are necessary to understand the short-term and long-term effects of the coronaviruses on the olfactory system.

What Are the Causes of Phantosmia?

Phantosmia is a rare condition and constitutes about 10 to 20 % of all the disorders that affect the sense of smell. The causes of phantosmia can be due to:

• Upper respiratory infections.

• Sinus infections.

• Nasal polyps (a non-cancerous growth on the lining of the nose or sinuses).

• Allergies.

• Colds and migraines.

• Certain medications.

• Exposure to chemicals like lead or mercury.

• Smoking.

• Dental problems like dry mouth or gum disease.

• As a consequence of COVID-19 infection.

Less possible causes of phantosmia can be Parkinson’s disease, stroke, head trauma, brain tumor, Alzheimer’s disease, depression, stroke, schizophrenia (a disorder that influences an individual’s ability to think, feel, and behave in a clear manner), epilepsy (a disorder in which there is a disturbance in the activity of nerve cells in the brain), and neuroblastoma (cancer in various areas of the body that originates from immature nerve cells).

Individuals with phantosmia may also experience a strong odor in one nostril than the other. Anesthetic pads and saline rinses can help one cope with phantosmia.

What Are the Signs and Symptoms of Parosmia and Phantosmia?

The severity of the symptoms of parosmia differs with each individual and is more obvious when one recovers from an infection. The signs and symptoms of parosmia are as follows:

• A sense of persistent foul odor.

• Difficulty in identifying certain smells due to damage to the olfactory neurons.

• Previously enjoyable and pleasant odors would seem to be strong and intolerable in the present. If one feels the smell of the food is bad, they may feel sick or nauseous while eating.

Individuals with phantosmia would describe the smells to be as follows:

• Rotten food.

• Burning rubber.

• Garbage.

• Chemicals.

• Burnt toast.

• A metallic odor.

• Tobacco smoke.

• A stale or moldy odor.

A few individuals might also sense smells with which they have not been familiar or cannot identify. Additional symptoms may be experienced based on the underlying causes or due to the presence of other comorbidities.

How Can Parosmia and Phantosmia Be Diagnosed?

• Diagnosis of Parosmia:

1. Parosmia is usually diagnosed by an otolaryngologist (an ear-nose-throat physician). The physician might introduce substances with varied odors to the person and ask them to describe and rank the odor.

2. A common diagnostic method to identify parosmia is using a small booklet of 'scratch and sniff' beads, to which one responds under the physician's supervision. The physician will also inquire about the previous history of recent infections, smoking habits, family history of neurological conditions or cancer, and current medications.

3. If any underlying neurological or cancer-related issues are suspected, the physician would ask one to take a sinus computed tomography (CT) scan, an MRI (magnetic resonance imaging), or a biopsy of the sinus area.

• Diagnosis of Phantosmia:

1. A physical examination of the head and neck may be performed initially by the physician. The physician might also inquire about the other symptoms and carry out certain tests to assess the person’s other senses.

2. An endoscopy (a test to view inside the body using a long, thin tube that has a small attached camera on one end) or rhinoscopy (examination of the inner aspect of the nose using a rhinoscope) may be suggested by the physician.

3. Specific or comprehensive tests may also be suggested, or the person might be referred to a specialist. Tests like CT scans, MRI scans, and EEG (electroencephalography) scans may sometimes be suggested to find any abnormalities in the brain, nasal cavity, or nervous system.

How to Treat Parosmia and Phantosmia?

• Treatment for Parosmia: The treatment of parosmia may be effective in a few but not in all cases. If parosmia is triggered by certain medications, environmental factors, smoking, or cancer treatment, the sense of smell may be restored once these triggers are eliminated. At times, surgery may be preferred to resolve parosmia. Nasal polyps, or tumors, if any, should be removed. The treatment for parosmia encompasses the following:

1. Vitamin A.

2. Antibiotics.

3. Zinc.

The use of the above requires more case studies and research. If parosmia influences one's appetite and weight, it is advisable to opt for olfactory training therapy (smell training therapy). In this procedure, one is purposefully made to sniff each of four different types of odors for 15 seconds. This is done twice daily for many months.

• Treatment for Phantosmia: The treatment of phantosmia depends on the underlying cause. If the disorder is due to a consequence of colds, allergies, or infections, then the olfactory hallucination (phantosmia) should cease after one recovers from the condition. Other treatment modalities are as follows:

1. The treatment of brain-related (neurological) cases of phantosmia could be difficult. Different types of treatments are available for different causes. For example, epileptic patients may require medication or surgery, while those with brain tumors would require radiation therapy or chemotherapy. Once the underlying cause is exactly determined, then appropriate treatment can be provided.

2. Allergies can be treated using steroids and allergy shots (injections given at regular intervals to cease or reduce allergy attacks).

3. One must quit smoking and refrain from getting exposed to known chemicals.

4. Certain medications that could trigger phantosmia include antibiotics and antidepressants. One must consult a physician and discuss how these medicines can be taken to prevent phantosmia.

5. If phantosmia is due to brain trauma or a viral infection, one must wait for the symptoms to settle on their own.

6. Home remedies could offer relief to persons with phantosmia. Rinsing the nasal passages with an over-the-counter saline solution or a neti-pot can be beneficial in those with phantosmia. The use of over-the-counter oxymetazoline spray can provide relief from nasal congestion.

Conclusion

Parosmia is a condition in which one experiences an altered odor of certain things due to damage in the olfactory system. It can occur due to infection, brain trauma, or other causes. It is not permanent; the neurons can regain their senses with time. The recovery rate of parosmia depends on the underlying cause and symptoms. Phantosmia is a condition in which one detects odors in the surroundings while it actually does not exist. It could occur as a consequence of colds, allergies, or upper respiratory infections. Phantosmia is mostly a temporary disorder that resolves within a few weeks. However, the symptoms may persist if the underlying cause is neurological. It is better to consult a healthcare professional if the phantom smells persist for over a few weeks.