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From 50 to 80 percent of people who have Parkinson's disease experience delusions and hallucinations at some time during the course of their disease. Early diagnosis improves quality of life, but Inappropriate medications can make the problem worse.

Parkinson's disease (also known as Parkinson disease) is a relatively common condition in older adults. In the United States, about one million people have the disease. Worldwide, about one person in 100 develops the condition. It is 15 times more common in men than in women. Although it is most frequently seen after the age of 65, Parkinson's sometimes strikes young adults.

The first symptom of Parkinson's disease often goes unnoticed. It is loss of sense of smell (hyposmia). There may also be changes in sleep patterns. Someone who has Parkinson's may make hitting or punching motions during sleep. They may "act out" their dreams by flailing around or by crying out. Toilet habits also change. There can be a lot of "gotta go" incidents of urgent urination, but constipation becomes a problem. Blackheads due to seborrheic dermatitis may pop out. 

As the usually-unnoticed changes progress, there can be subtle losses of dexterity. It may become harder to button a shirt or a blouse, or hold a golf club or tennis racket. There usually is a tremor that affects just one side of the body. There may be also a loss of facial expression and softening of the voice.

The disease causes a slowing of movement (bradykinesia) and "freezing." The first-affected arm may not move during walking. A foot may scrape the floor. Over time standing posture becomes progressively stooped, and motion becomes more and more difficult. 

Parkinson's disease usually starts with resting tremors. A thumb or a finger, sometimes the wrist or a forearm on one side of the body may "take off" with a kind of tremor that can't be voluntarily duplicated. Initiating a motion with those muscles stops the tremor. Both sleep and stress make tremors stronger.

Parkinson's dementia

Subtle changes in thought processes also occur in Parkinson's, even early in the disease. A study of Parkinson's patients in Norway found that 19 to 42 percent had some degree of forgetfulness or loss of mental abilities when they were first diagnosed, but not enough to interfere with daily activities. For these patients, the diagnostic term is Parkinson's disease with mild cognitive impairment (PD-MCI).

Most people with PD-MCI aren't like the Parkinson's patient who sees an imaginary dog in the TV commercials for a medication sold in the US (linked below). They don't see things. They don't talk to people who aren't there. They don't smell strange smells or have delusions of persecution or abandonment. About 10 percent of people who have PD-MCI regain normal cognition during the course of the disease rather than developing dementia. So how can you tell if you need to begin drug treatment to stop the progress of dementia, or you may be one of the more fortunate patients who will never develop it? Until recently, there were no medical tests to answer these questions.

Predicting Parkinsonian dementia

Until recently, there were no medical tests that could predict dementia in Parkinson's disease. That is because brain scans measured the extent of neuron death that only occurs in the later stages of the disease. Since about 2010, neurologists have recognized that there are two different patterns in the early stages of Parkinson's disease.

  • One is a pattern of damage in the front of the brain. It's related to a failure of dopamine production for the parts of the brain that perform "executive" functions. 
  • The other is a pattern of damage in the back of the brain. It's related to problems with a different chemical. The back of the brain is involved in the processing of visual information, and dysfunction here is linked to hallucinations.

Conventional management of Parkinson's "works" for the pattern of damage in the front of the brain. It doesn't work for the pattern of damage in the back of the brain. Images of the brain with PET or SPECT scans rather than just with MRI and CT scans can help the neurologist recognize which parts of the brain are affected by the disease. Taken together, these diagnostic techniques can identify which kinds of deterioration (muscle function, language, reasoning, hallucination/delusions) are most likely so preparations are possible.

'When we look for things, we find them'

Many Parkinson's patients find the process of advanced imaging and diagnosis to be an exercise in "too much information." When neurologists start looking for indicators of disease processes in the brain, they usually find them. Sometimes you'd rather just not know.

So let your neurologist manage your disease, while you manage your life. Just be sure that you have one neurologist who knows all of your medications and all of your treatments so you receive optimal treatment for staying as healthy as possible as long as possible.

Several of the most common medications in the United States counteract the drugs used to treat Parkinsonian dementia. These include diphenhydramine (Benadryl), oxybutynin (Ditropan), and paroxetine (Paxil). Not only do they interfere with medications to prevent hallucinations and delusions such as donepezil (Aricept), galantamine (Razadyne), and rivastigmine (Exelon), they can trigger psychotic symptoms on their own.

  • Aarsland D, Brønnick K, Larsen JP, Tysnes OB, Alves G. Cognitive impairment in incident, untreated Parkinson disease: the Norwegian Parkwest study. Neurology 2009. 72: 1121–26.
  • Agosta F, Canu E, Stefanova E, Sarro L, Tomić A, Špica V, et al. Mild cognitive impairment in Parkinson's disease is associated with a distributed pattern of brain white matter damage. Hum Brain Mapp 2014. 35: 1921–9.
  • Mantri S, Fullard M, Gray SL, Weintraub D, Hubbard RA, Hennessy S, Willis AW. Patterns of Dementia Treatment and Frank Prescribing Errors in Older Adults With Parkinson Disease. JAMA Neurol. 2019 Jan 1.76(1):41-49. doi: 10.1001/jamaneurol.2018.2820. PMID: 30285047.
  • Photo courtesy of SteadyHealth

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