Parosmia is a condition where the brain is unable to recognize the natural smell of something, leading to the perception of unpleasant or distorted smells. It can be caused by upper respiratory tract infections, head trauma, epilepsy, and Parkinson’s disease. There is no specific treatment, but symptoms may lessen over time. Diagnosis involves testing the sense of smell using different scents.
Also called troposmia, parosmia is the impairment of olfactory function leading to the brain’s inability to recognize the natural or inherent smell of a particular smell. Natural odor is therefore usually perceived as a rotten, burnt, faecal or chemical odor. In cases where pleasant odors are perceived instead, the olfactory dysfunction is more properly called euosmia. Causes include upper respiratory tract infections, head trauma, temporal lobe epilepsy, and Parkinson’s disease. There is no specific treatment available, but the severity is known to decrease over time.
Parosmia is the term used to refer to distorted sense of smell, where the affected person perceives an odor that deviates from the typical scent. For example, the person concerned may be presented with an apple scent, but instead perceives a burning smell. Conversely, phantasmia refers to the perception of smell when there is no scent or smell presented. Phantosmia more accurately refers to olfactory hallucinations.
Various unpleasant odors reported by people who have the condition include garbage, vomit, smoke, and rotting meat. Most people identify the smell of rotting meat as the most unpleasant. Normally, people who smell unpleasant odors undergo a sensory adaptation, so that within minutes the unpleasant smell seems to have dissipated. Among people suffering from parosmia and phantosmia, the perception of the unpleasant odor is long-lasting. The unpleasantness of the odor and the long duration of perception of this odor usually lead those affected to a medical examination.
Diagnosis involves testing the affected person’s sense of smell by presenting with different smells. Methods include the University of Pennsylvania Smell Identification Test (UPSIT) and sniff sticks. When these methods are used, the stimulating odor can be identified.
The main cause of parosmia is upper respiratory tract infections (URTIs). It is hypothesized that URTIs may damage olfactory receptor neurons (ORNs), leading to the inability of these neurons to encode and send the correct signal to the olfactory bulb, which serves as the odor processing center. Exposure to solvents, such as benzene, is also associated with this impairment of smell due to ORN damage.
A head injury that affects the olfactory bulb, which is located in the lower part of the brain, can also lead to this condition. Any pathology involving the interpretation centers of the brain can lead to misperception of smell. Episodes of olfactory dysfunction following temporal lobe seizures have been reported. Among people with Parkinson’s disease, it is speculated that insufficient levels of dopamine lead to the condition.
There is no definitive cure for parosmia, but its symptoms do lessen over time. Some people can suffer for years. Levo-dopamine has been used for some people, but there is no evidence that it cures the condition. Some patients who prefer not to smell anything choose to have their olfactory bulb destroyed with surgery.
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