Hallucinations are a common symptom of Parkinson’s disease, with around a quarter of patients regularly experiencing them. Visual hallucinations are the most common, often involving moving, blurry images. Causes include medication, weakened vision, depression, and mental impairment. Treatment involves reducing medication doses and using antipsychotic drugs, but their impact on motor function is a concern.
Hallucinations are a common symptom of Parkinson’s disease. However, estimates for the exact frequency vary. One evaluation suggests that a quarter of patients hallucinate regularly and about half have experienced a hallucination at some point in the course of their illness. The causes and timing of these hallucinations are complicated.
Hallucinations in Parkinson’s are usually relatively minor. One of the more common hallucinations reported is simply a feeling of presence: a feeling that a being is nearby. Visual hallucinations are the next most common, followed by auditory hallucinations, which only rarely occur independently. These visual hallucinations often involve a complicated, moving, blurry image. In this respect Parkinson’s differs from other hallucinogenic diseases such as schizophrenia. The hallucinations can, however, sometimes be part of a larger psychotic complex involving paranoid delusions.
Several factors have been identified as causes of hallucinations in Parkinson’s. The older explanation is that Parkinson’s drugs are responsible. It has been suggested that levdopa, which the body turns into the neurotransmitter dopamine, is the main culprit. Monoamine oxidase inhibitors have similar and perhaps more widespread effects. Of all the dopaminergic drugs, dopamine agonists appear to be the most hallucinogenic. Anticholinergic drugs, sometimes used to treat Parkinson’s, are independently known to be associated with hallucinations.
A 2000 study by Fénelon, Mahieux, Huon, and Ziégler, published in the Brain, yielded a number of other explanations. They found that the hallucinations were related not only to the drugs but also independently to a variety of other symptoms associated with Parkinson’s. For example, the weakened vision caused by the disease has also increased the likelihood of hallucinations. Depression, disability, unusual daytime sleep, and general mental impairment are all symptoms of Parkinson’s that also correlate with an increase in the number of hallucinations.
The study also found that the hallucinations were more frequent at night and after a longer duration of illness, although they appear to occur somewhat erratically. The researchers also caution that hallucinations in Parkinson’s patients appear to be relatively underreported. This may be because patients fear insanity or because many of the episodes are minor.
Subsequent studies confirmed the team’s 2000 findings, finding that any of several factors can cause hallucinations in Parkinson’s patients. Regardless of the variety of causes, it has been found that reducing medication doses can improve the condition. Antipsychotic drugs to treat these side effects have also enjoyed more widespread use. The benefit of these drugs, however, has yet to be balanced against their contribution to the deterioration of motor function.
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