The cause of<unk>  can be either peripheral or central, or a combination of the two. The peripheral explanation of this disorder is that rogue neurons malfunction and transmit incorrect signals to the brain or it may be due to the malfunction of the olfactory neurons. The central explanation is that active or incorrectly functioning cells of the brain cause the perception of the disturbing odor. Another central cause is that the perception of the phantom odor usually follows after the occurrence of seizures. The time span of the symptoms usually lasts a few seconds. Other studies on<unk>  patients have found that the perception of the odor initiates with a sneeze, thus they avoid any nasal activity. It has also been found that the perception of the odor is worse in the nostril that is weaker in olfaction ability. It has also been noted that about a quarter of patients suffering from<unk>  in one nostril will usually develop it in the other nostril as well over a time period of a few months or years. Several patients who have received surgical treatment have stated that they have a feeling or intuition that the phantom odor is about to occur, however it does not. This sensation has been supported by positron emission tomography, and it has been found that these patients have a high level of activity in their contralateral frontal, insular and temporal regions. The significance of the activity in these regions is not definitive as not a significant number of patients have been studied to conclude any relation of this activity with the symptoms. However the intensity of the activity in these regions was reduced by excising the olfactory epithelium from the associated nasal cavity. There are a few causes for<unk> , but one of the most common and well-documented involves brain injury or seizures in the temporal lobe. During a temporal lobe seizure the victim rarely faints, but usually blacks out and cannot remember anything that happened during the seizure. Several people who have had these seizures did, however, recollect having<unk>  just prior to blacking out. Epilepsy is a disease characterized by seizures. In the case of<unk> , if smelling and something else become so strongly linked, the action of "something else" occurring can induce activation of the olfactory bulb even though there was no stimulus for the bulb present. This is an example of plasticity gone awry. Those with lesions on the temporal lobe, often brought about by a stroke but also from trauma to the head, also experience these olfactory hallucinations. Other leading causes of<unk>  include neurological disorders such as schizophrenia and Alzheimer's disease. Both of these disorders have well documented cases of hallucinations, most commonly visual and auditory. Both also, however, have instances of<unk>  too, although not as frequently. In both cases, incidences of olfactory delusions are more common, especially in Alzheimer's, where it is exceedingly difficult to convince the patient that these are in fact hallucinations and not real. Specifically in Alzheimer's disease, atrophy in the temporal lobe has been known to occur. As evidenced in trauma and seizures,<unk>  is strongly associated with this area; leading to its appearance in some Alzheimer's patients. Parkinson's disease patients can also experience<unk> , as well as parosmia, however their appearance is less common than the muscle tremors the patients experience. Neuroblastoma Neuroblastoma is a rare form of a malignant cancer which can start in the olfactory nerve, which is responsible for smell sensation. This cancer can become aggressive and progress into the ethmoid sinuses, brain cavity, surrounds the cribriform plate. The tumor can be tested for by performing a surgical biopsy and the possible treatment options include surgical removal of the tumor, radiation therapy and chemotherapy, which can cause damage to the olfactory system and possibly result in<unk> , in turn. Development The complaints of<unk>  involving the perception of unpleasant odors most commonly include "burnt", "foul", "rotten", "sewage", "metallic" or "chemical". Sometimes the odor is described as exhaust fumes. These odors may be triggered by strong odorants, changes in nasal airflow, or even loud sounds. Sometimes they occur spontaneously. Patients having complaints of<unk>  might self-admit a poor quality of life, with each meal having the unpleasant odor as well. The disorder's first onset, usually spontaneous, may last only a few minutes. Recurrences may gradually increase from monthly, then weekly, and then daily over a period of six months to a year. The duration of the perceived odor may also increase over the same time, often lasting most of a day after one year. Some patients also state that the odor they smell is different from any known odor.
Phantosmia
Ocular dysmetria
Buphthalmos
Anosmia
Nyctalopia
Dysosmia
Dysmelia
Aspermia