Olfactory hallucinations


Olfactory hallucinations

Description, Causes and Risk Factors:

False perception in smell.

Many people are sensitive to certain smells, but in an olfactory hallucination, you detect smells that are not really present in your environment. Olfactory hallucinations are perceived abnormal smells — usually unpleasant — that are not actually present in the physical environment. They can come from a number of different areas of the smell system. The length of time these smells last depends on the cause. If the smell of smoke occurs suddenly and continues for less than a few minutes, the site of origin is likely the smell region of the inner temporal lobe of the brain called the uncus. The source could be an abnormal electrical discharge or "firing" in the brain (a seizure). Potential causes of this abnormality could be a brain tumor, inflammation, stroke, or an injury following head trauma.

Olfactory hallucinations lasting more than a few minutes to several hours are usually due to a disturbance of the smell system in the nose (olfactory organ or olfactory nerves) or in the olfactory bulb, which sits just inside the skull above the upper nose level.

Common causes of olfactory hallucinations are head and nose injury, viral damage to the smell system after a bad cold, chronic recurrent sinus infections and allergy, and nasal polyps and tumors. The brain is usually not the source. In these instances, sense of smell for other odors is often impaired as well, and the results of smell testing typically are abnormal. It can also be caused by temporal lobe seizures, sinusitis, brain tumors, migraine, Parkinson's disease and stroke.

People with severe psychiatric disorders may have profound chemical imbalances in their brains which trigger the chemosensory system which allows people to perceive smell, creating a hallucinatory experience.

The odors detected in olfactory hallucinations vary from person-to-person and may be foul or pleasant. They can occur in one or both nostrils and usually cannot be masked by food. Because olfactory hallucinations in rare cases can be an indication of a serious underlying disorder, consult your doctor if you experience such symptoms.

Symptoms:

Symptoms may include:

    Aura.

  • Migraine headaches.

  • Cluster headaches.

  • Chronic headaches.

These hallucinations can be very unpleasant for those experiencing them, they are very interesting for researchers trying to understand how the sense of smell works. It has, for example, been proposed that the fact that some people who lost their sense of smell still experience specific and identifiable phantom smells shows that the identity of a smell does not depend on what receptors in the nose are activated, but on a higher cognitive function.

Diagnosis:

Confirming the cause requires an imaging study of the brain (MRI) and a brain-wave test, electroencephalography (EEG). Usually, results of smell testing will be normal to minimally abnormal in a person who is experiencing this type of seizure. If a seizure disorder is suspected, antiseizure medications may be used to prevent a seizure and thus eliminate the smell. A nasal endoscopy, in which an Ear, Nose, & Throat (ENT) physician looks inside nasal and sinus passages may be useful.

Treatment:

Olfactory hallucinations usually disappear with time (three months to two years) without treatment. Olfactory hallucinations can be treated with normal saline nose drops administered with the head lowered (the top of the head should be pointing to the floor). It may also improve with some medications, such as gabapentin — a medication normally used for seizure disorders but that has also been shown to prevent unpleasant odors arising from injured smell receptors or their nerve branches. The use of gabapentin in this instance is considered off label, which means it is not approved by the FDA for this indication. This doesn't mean the medication is not effective and safe, but rather that the drug has not been officially studied and evaluated by the FDA for this condition.

NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

4 Comments

  1. Michael abelson

    My wife 67 year old wife keeps smelling unplesanr orders I can’t sense. Over 20 years ago she had an acoustic neuroma successfully removed. This has gone on for years. Could there be a causal relationship?

    Reply
    • maisteri

      It is unlikely that acoustic neuroma is related to the symptoms which are present now. However, your wife should visit a neurologist and an MRI should be performed to verify the cause of the condition.

      Reply
  2. Craig

    Two years ago, I was the recipient of a rear-end collision at freeway speed two years ago. Since then, I have experienced almost daily olefactory hallucinations. Should I seek medical help? What type(s) of testing/treatment should I expect?

    Reply
    • maisteri

      You should see a neurologist and explain him the situation. Olfactory hallucinations may be related to the traumatic brain injury you’ve experienced. Brain MRI may be necessary to check whether there is a lesion or not.

      Reply

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