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Olfactory Hallucinations: Smells That Lie

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Olfaction is an important aspect of otolaryngology. Read this article to understand the various aspects of smell and false smell perception.

Medically reviewed by

Dr. Samarth Mishra

Published At November 4, 2022
Reviewed AtNovember 4, 2022

Introduction

Olfaction is an important aspect of otolaryngology. Unfortunately, per many ENT doctors, this is a slightly neglected topic for various reasons, such as the difficulty of investigating and diagnosing the olfactory sense organs, the overlapping among different medical specialties related to olfaction, and the absence of community awareness of the olfactory disorders.

What Are Olfactory Hallucinations?

Olfactory hallucination is a common symptom which is the false perception of a smell without any constant real source. To understand olfactory hallucinations, one should first know some facts about general olfaction.

Mammals use their noses to smell, but actually, they smell by using their brains. The nose is just a passage and a receptor station for the process of olfaction, while the brain is the actual site of smell perception.

How Is Olfactory Hallucination Clinically Classified?

Clinically smell hallucinations can be classified into simple and complex types. The simple type is when the patient reports a perception of a certain odor without an authentic source. In the complex type, the patient provides additional information related to the odor, like associated feelings such as happy or sad memories and localization of the source( whether inside or outside the body cavity).

It is important to differentiate between hallucination and pseudohallucination. Hallucination is illustrated as false sense perception despite the absence of a stimulus, while pseudohallucination is when the patient experiences false perceptions knowing that he is going through an illusion and the stimulus is absent.

What Is Olfactory Delusion?

In all types of olfactory hallucinations, the patient reports smelling an odor that has been experienced before, which means that smelled odor is familiar, while when the patient s smells a new odor that has not been experienced before, despite the absence of a stimulus, is called an olfactory delusion.

What Are Olfactory Distortions?

Olfactory distortions differ from olfactory delusions by the fact that there is a presence of a true source of the smell. It means that in olfactory distortions, the source of the smell is truly present. There are two types of olfactory distortion, negative and positive types. In the negative type, there is a loss of function where the smell sense is not strong enough to detect the smell of an existing stimulus fully. The negative type is medically expressed as anosmia, hyposmia, or microsmia. In the positive type, there is no loss of function, but the patient smells something different than the actual smell of the stimulus.

Although the medical differences between olfactory delusion and distortion look clear, in clinical practice, it is difficult to differentiate between true olfactory hallucination and dysosmia as the source of the foul odor may be internal, like mouth, nose, sinuses, and stomach. Hence, the diagnosis depends basically on the clinical sense of the physician and not solely on the patient's words.

Which Conditions Are Associated With Olfactory Hallucinations?

Some of the diseases in which olfactory hallucinations are involved are

1. Neurological Syndromes:

Epilepsy-

Epilepsy is seizures accompanied by sudden deterioration of consciousness. An epileptic patient can experience olfactory hallucinations before or during the attack. Olfactory hallucinations in an epileptic patient can happen for a few minutes to several days before the epileptic fit. According to the patients, the type of perceived odor differs from one patient to another and from one attack to another attack of the same patient. The perceived odor ranges from unpleasant odors like the smell of rotting meat, decayed animals, burning rubber, wood, and tar to pleasant odors like that of fruits, flowers, and spices.

Destructive Lesions-

This can be classified into central and peripheral lesions. Central lesions are those affecting the central nervous system, particularly the temporal and frontal lobes of the brain, like temporal neoplasms such as gliomas, temporal lobe trauma, anoxia, stroke, and infections such as herpes simplex encephalitis. Other tumors affect other brain sites but can also affect olfaction, such as olfactory groove meningiomas and pituitary adenomas.

Peripheral damage to peripheral olfactory structures as peripheral olfactory nerves results in disturbance in smell perception. For example, upper respiratory tract infections, usually known to cause temporary and sometimes permanent loss of smell sensation, are also considered a cause of olfactory hallucinations. Still, these symptoms go unreported by the physicians or unnoticed by the patient.

Migraines-

Migraine is usually known for its famous symptoms that precede the migraine attack from five to twenty minutes, like nausea, vomiting, and simple visual hallucinations. Few cases are reported to have additional olfactory hallucinations besides the classical symptoms. Although the mechanism of migrainous olfactory hallucinations is not clear, the mechanism of migrainous visual hallucinations is better understood.

2. Psychiatric Syndromes:

Schizophrenia-

Olfactory hallucinations are not usually reported in schizophrenic patients because the patients tend to overcome this complaint as they have more annoying complaints as auditory and visual hallucinations. Upon enquiring about olfactory hallucinations, individuals may report experiencing them many times, failing to report them, and being more concerned about auditory and visual hallucinations. The type of odors reported in schizophrenic patients is a mixture of noxious and fetid fumes like fecal and other bodily odors. Patients usually tend to localize the source of the odors as an external source away from their bodies. The mechanism of schizophrenic olfactory hallucinations is unknown, but it is believed to be of central origin.

Olfactory Reference Syndrome (ORS)-

ORS is very different from schizophrenia. In ORS, olfactory hallucination is the main complaint that guides the patient to consult many specialists, including dentists, otolaryngologists, and pulmonologists, to get rid of the offensive odor. In ORS, the patient attributes the offensive odor to his own body, especially to any bodily orifice such as the anus and mouth. The offensive odor in ORS is primarily constant and can not be named. A patient with ORS faces social problems such as withdrawal from social events and intense shame. Because of the absence of visual hallucinations, auditory hallucinations, and any other thought disorders in ORS, some scientists call it solitary psychosis.

Depression-

Olfactory hallucinations can be a symptom of major depression. Depression is characterized by a lack of appetite, weight loss, recurrent gastrointestinal disturbances, and forbearers of negative thoughts such as death and despair, which are linked to guilt and shame.

The type of smell perceived varies according to the mood of the depressed patient; it can be a rotting or a decaying odor. Additionally, a patient with major depression usually neglects personal body hygiene, especially oral hygiene, which can be a real source of a bad smell.

There are some important differences between olfactory hallucinations of major depression and olfactory reference syndrome. In ORS, the patient usually denies any strong negative feelings except for their feeling of social shame. In contrast, in major depression, the patient always has negative feelings and horrible imagination, which seem to be constant and permanent. In major depression patients, the negative imagination and sad feelings preceded olfactory hallucinations, while in ORS, olfactory hallucinations are reported first, with the feeling of shame following second. Olfactory hallucinations of major depression show a great response to aggressive anti-depressant drugs.

Post-Traumatic Stress Disorder (PTSD)-

Post-traumatic stress disorder (PTSD) is a group of emotional and psycho-physiological reactions following events like battlefield injuries, endangering the life of a victim or a civilian, disasters, car accidents, or rape.

When someone is exposed to a catastrophic event, an actual strong odor during the event may get imprinted in the brain. Later in life, if the person experiences the same odor again, it triggers a brief state of conscious alteration, known as an olfactory flashback. Olfactory flashback can be triggered by exposure to a similar odor or any other stimulation. Olfactory flashback is preceded by a period of suppression of the whole memories related to the causative trauma. Then, step by step, the memories break their way into the victim's consciousness in the form of intrusive images and repetitive nightmares until the state of olfactory flashback goes away.

The mechanism of olfactory hallucinations in PTSD is unknown. Although olfactory hallucinations are not always common in PTSD, it gives us a great idea about the formation of emotional memories.

Conclusion

Olfactory hallucinations are a real condition, whatsoever may be the stimulus. Unfortunately, the complaint is often masked by the patient or ignored by the examining physician. Apart from pharmacotherapy, the patients require counseling and therapy. The treatment requires multidisciplinary care ranging from neurologists, otolaryngologists, and psychologists.

Dr. Mohammed Osama Aboborda
Dr. Mohammed Osama Aboborda

Otolaryngology (E.N.T)

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