Lack of Research and Way of Measuring Visual Hallucinations in Parkinson’s Hinders Its Treatment, Study Says

Research into the best ways of managing visual hallucinations in patients with Parkinson’s disease over the long term is severely limited and affecting treatment, a review study has found.

In particular, the lack of a universal rating scale renders data interpretation and comparison between studies difficult. To overcome this limitation, researchers propose the creation of a specific scale suitable to monitoring the effects of pharmacological and non-pharmacological treatments for visual hallucinations.

The study, “Management of visual hallucinations in dementia and Parkinson’s disease,” was published in International Psychogeriatrics.

Visual hallucinations — seeing something that is not real — is a common symptom of Parkinson’s and other types of dementia, including Alzheimer’s disease, dementia with Lewy bodies and frontotemporal dementia. These symptoms can be quite disturbing for patients, and are associated with rapid cognitive decline and increased mortality.

Although a large number of pharmacological and non-pharmacological therapies have been proposed to treat such hallucinations, an optimal management strategy is yet to be found.

This systematic review examined the prevalence and risk factors of visual hallucinations, as well as rating scales and therapeutic approaches that have been proposed to monitor and minimize their occurrence.

After a thorough literature search in the PubMed database, a total of 89 relevant studies (11 meta-analyses, 34 randomized controlled trials, six other trials, and a number of relevant review articles) were selected.

Previous studies estimated the prevalence of visual hallucinations for Alzheimer’s disease to range from 3% to 76%, and from 22% to 38% in people with Parkinson’s disease.

The high variability in prevalence, especially in Alzheimer’s disease “may be due to the setting of the study population (clinic vs. nursing home) and differences in who the informant is; whether patient, relative, or professional,” the researchers wrote.

Among Parkinson’s patients, the biggest challenge to determining prevalence of visual hallucinations seems to be separating “the contribution of dopaminergic and anticholinergic drugs from that of the disease.”

In dementia with Lewy bodies and frontotemporal dementia patients, prevalence is estimated to be 15-20% and 14.4%, respectively.

Non-pharmacological strategies have been proposed mainly as a first-line treatment for visual hallucinations. However, solid evidence from controlled trials that might demonstrate therapeutic benefit specifically for visual hallucinations is lacking.

“[R]eviewers have recommended increased socialization, as well as improving lighting and reducing visual triggers, but admit this because they are useful and inexpensive rather than based on trial evidence,” the researchers wrote.

Antipsychotics — both typical and atypical — are commonly used to treat psychosis and depression, but when used in patients with dementia are associated with a series of adverse side effects, including increased risk of stroke and death. Still, these medicines may continue to be prescribed off-label to these patients, mostly due to a lack of better alternatives.

In Parkinson’s disease, several antipsychotic treatments have been tested over the last few years. While some, like melperone and Zyprexa (olanzapine), clearly failed to ease psychosis and delusions, Clozaril (clozapine) and Nuplazid (pimavanserin) were seen to treat psychosis and hallucinations without impairing patients’ motor functions. The effects of others, like Seroquel (quetiapine), vary substantially across studies and are difficult to interpret.

In any case, these medications — even Nuplazid, the only medication approved by the U.S. Food and Drug Administration (FDA) for Parkinson’s delusions and hallucinations — “still carry the same black box warning as other antipsychotics for older people with dementia” and should be used with caution.

One of the key limitations encountered by the researchers that affects not only data interpretation, but also its generation, was the lack of a specific universal rating scale to assess visual hallucinations. Rather, symptoms tend to be “grouped together as all ‘hallucinations’ or ‘psychosis’. This over simplifies symptoms and prevents an understanding of what treatments may or may not work,” they said.

“We recommend the development of a specific scale suitable for natural history and treatment studies of VH, and for larger multi-site studies of both non-pharmacological and pharmacological treatments for VH [visual hallucinations],” the researchers concluded.