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Dysosmia is a neurological disorder that causes an altered sense of smell. The condition can manifest itself in a variety of ways: it may distort smells, which a sub-condition called parosmia; initiate no olfactory response at all, called anosmia; or produce smells that aren't there, called phantosmia. Since the oral cavity and the olfactory system are interrelated, some patients with dysosmia may develop issues with their sense of taste as well.
The three sub-conditions that comprise this type of olfactory dysfunction each possess their own respective set of characteristics and possible causes. Individuals with parosmia cannot properly identify smells, which is commonly presented as a neutral or pleasing scent being interpreted as an unpleasant one. The condition may apply to specific odors or any odor at all, depending on the pathology of the patient. Parosmia can be caused by several different conditions, including upper respiratory ailments, exposure to toxic chemicals, or various types of brain injuries.
Anosmia is distinguished by the inability to smell. Like parosmia, it can be specific to certain scents or can encompass any and all scents. With anosmia, the olfactory bulb is not triggered by the scent of the stimuli and no odor is detected. Anosmia can be the result of any number of conditions, including a blocked nose, infection of the sinuses, genetic predisposition, brain injury, Alzheimer's disease, or Parkinson's disease. It may also result from an overuse of certain types of nasal sprays, which damage neurons in the olfactory system.
Phantosmia can be characterized by smelling odors that do not come from a physical source. They are, in essence, hallucinations of the olfactory system, and, in most cases, are exceedingly unpleasant. Neurological disorders in which the neural pathways of the brain become twisted together are the most common causes for phantosmia. Epilepsy, schizophrenia, Alzheimer's disease, and head trauma can all lead to phantosmia.
Any of the three subsets of dysosmia can be diagnosed through a standard olfactory test administered by a specialist. In this screening, patients are given scented samples to smell and identify, and their responses are measured and recorded. The testing process, however, will not identify the cause of the disorder.
There is no definitive treatment for dysosmia. In some cases, the condition will go away on its own. Experiments in treating parosmia with the drug L-Dopa were conducted during the 1970s, but no conclusive results were reached. In the case of phantosmia, a surgery known as an olfactory epithelium has shown positive results in eradicating the condition.