Phantosmia, from the Greek phant- meaning phantom and osme meaning smell, is an olfactory hallucination. The disorder is frequently associated with neurological and psychological conditions. Some of these conditions include migraines, epilepsy, Parkinson’s disease, neuroblastoma (cancer of neural tissue), and schizophrenia. Causes of the disorder vary, and the smells patients experience can be anywhere on a scale of pleasant to disgusting. Phantosmia can be classified into three main categories: unirhinal (from one nostril), episodic, and recurrent. Since the causes of phantosmia are varied and some are psychological rather than physiological, there is no defined treatment. For serious cases, surgery can be performed to remove the olfactory bulb. This results in anosmia, or the complete lack of sense of smell, which would also affect the flavor of food. Thus, the surgical option is not highly valued.
Causes and Diagnosis
There are a wide variety of causes of phantosmia including both neurological and psychological causes. These include less severe causes such as smoking, dental problems, nasal infection (the phantosmia typically disappears after the infection has cleared in this case), migraines (especially migraines with auras where the smell can occur before or during the migraine), nasal polyps (abnormal growths within the nasal cavity that can be either malignant—a precursor to cancer, or benign—a relatively harmless growth), and exposure to some chemicals (this includes insecticides and solvents). More severe causes of phantosmia include: schizophrenia, Alzheimer’s disease, Parkinson’s disease, cancer, stroke, and head injury. Additionally, the cause in some afflicted individuals can be purely psychological. One very well-documented cause of phantosmia is epilepsy involving seizures within the temporal lobe. Following seizure some patients reported phantom smells right before the seizure. Patients who do not experience seizures but have tumors growing within the temporal lobe also have a higher risk of phantosmia. In these neurological causes the issue can be that nerves are misfiring, sending the incorrect information to the brain, or the problem could be within the brain itself and how it processes these signals.
In order to diagnose phantosmia the physician needs to distinguish the condition from a gustatory issue (since the two systems are so interconnected) and from other olfactory conditions such as anosmia and parosmia (where the smell is coming from an object within the environment but this smell is becoming distorted). Both of these are typically due to damage of the olfactory system. During diagnosis, the physician will also attempt to discover the cause for the phantosmia. Techniques include nasal endoscopy (using a small flexible camera to examine the nasal cavity), a full medical history (especially looking for signs of head trauma and upper and lower respiratory infections), and imaging techniques (to look for seizures and cancers that could be the cause).
Symptoms and Treatment
The primary defining symptom of phantosmia is the perception of a smell when there is no odorant present. Phantosmia is typically worse in one nostril than the other, typically the nostril with the lower ability for smell. Scientists distinguish the terms phantosmia and olfactory hallucinations based on how long the symptoms persist. Olfactory hallucinations are the perception of a smell without an odorant present that lasts for only a few seconds. As such, phantosmia is the perception without odorant stimulus that persists for longer than a few seconds. Often, patients also report the feeling of the phantosmia about to happen. This feeling persists even after treatment to remove the smell. In this situation, patients still report the same feeling of the phantosmia about to occur but it never does.
One of the biggest ways to treat phantosmia is to treat the underlying cause of the disorder. For example, if epilepsy and seizures of the temporal lobe are what is causing the phantosmia, the reduction of seizures should help alleviate phantosmia for the patient. Sometimes the symptoms of phantosmia will reduce and eventually disappear with time, so one possible treatment for patients who can handle the smells is to wait it out and continue to monitor for a more serious neurological condition that could be the root cause. Some drugs that are used to treat depression and epilepsy have also been shown to be effective treatments in some cases. Finally, surgical treatment is an option. This can include removal of the olfactory epithelium (which has been shown to be fairly effective in a majority of cases) or removal of the olfactory bulb. One side effect of the removal of the olfactory bulb is that it can often lead to anosmia.
Riannon C. Atwater
See also: Anosmia; Dysosmia; Olfactory System
Leopold, Donald. (2002). Distortion of olfactory perception: Diagnosis and treatment. Chemical Senses, 27(7), 611—615. Retrieved from http://chemse.oxfordjournals.org/content/27/7/611.full
NHS Choices. (2014). Phantosmia (smelling odours that aren’t there). Retrieved from http://www.nhs.uk/conditions/phantosmia/Pages/Introduction.aspx