Visual Perception Test Distinguishes AD From Lewy Body Dementia Visual Perception Test Distinguishes AD From Lewy Body Dementia

A quick and easily administered test that measures visual perception can accurately distinguish mild to moderate dementia associated with Lewy body disease (LBD) from dementia associated with Alzheimer’s disease (AD), new research suggests.

The two dementias are similar and many patients with LBD also have AD. However, those with LBD can respond differently to many common dementia medications, underscoring the importance of diagnosis, researchers note.

Study results showed that performance on the Fragmented Letters Test (FLT) effectively differentiated patients with LBD pathology from those with only AD pathology at a mild to moderate stage of dementia — even when LBD occurred with significant concomitant AD pathology.

David Salmon, PhD

“There is currently no way to definitely determine if someone with mild or moderate dementia has cognitive impairment due only to AD pathology or to a combination of AD and Lewy body pathology,” lead investigator David Salmon, PhD, professor of neurosciences at University of California, San Diego, told Medscape Medical News.

“Our study demonstrates that the FLT works well to distinguish those with dementia with Lewy bodies with concomitant AD pathology from those with ‘pure’ AD pathology,” Salmon said.

The findings were published online August 26 in Neurology.

Missed and Mis-Diagnoses

Dementia with Lewy bodies (DLB) is the second most common form of progressive dementia after AD.

Patients with the condition may have visual hallucinations and changes in alertness and attention. Other symptoms mirror muscular and movement problems that are common in Parkinson’s disease, including rigid muscles, slow movement, walking difficulty, and tremors.

In its 2017 consensus report, the Dementia with Lewy Bodies Consortium warned of suboptimal detection rates in clinical practice, noting that many cases are missed or misdiagnosed as being AD.

In some cases, the clinical profile of DLB can actually look more like AD dementia, making it even harder to tell the two apart.

“The distinction is important to make because there may be differences in prognosis for the two conditions, such as faster decline and increased risk of the development of visual hallucinations in DLB,” Salmon noted.

“In addition, potential new therapies that specifically target one pathology, such as an amyloid-beta directed antibody like aducanumab, may not be as effective in someone who has both AD and Lewy body pathology,” he said.

Patients with DLB have been shown to perform worse than do those with AD on tests of visual object perception, visual search, visual motion discrimination, visual texture recognition, copying or drawing two-dimensional figures, and constructing three-dimensional objects.

So, Salmon and colleagues used the FLT, a component of the Visual Object Space Perception (VOSP) test battery, in the current study. It measured visuoperceptual ability, an aspect of visual perception that enables recognition of objects based on their form, pattern, and color.

Perceptual Deficits

The study included patients with mild cognitive impairment or dementia who were eventually confirmed at autopsy to have Lewy body disease (n = 19) or AD (n = 23). Also included were 22 “healthy controls.”

All were part of a larger, longitudinal AD study and had received annual physical, neurologic, and neuropsychological assessments, including the FLT and additional visuospatial and episodic memory tests. With the FLT, participants identified letters of the alphabet that were randomly visually degraded by 70%.

Results showed FLT scores for patients with AD were similar to those of the healthy controls group. However, the LBD group performed worse than both the control group (P = .01) and the AD group (P = .009).

The test effectively distinguished between patients with LBD or AD with 73% sensitivity and 87% specificity.

“In previous studies, we have shown that the presence of notable visuospatial deficits in patients with DLB is a harbinger of more rapid global cognitive decline and the subsequent development of visual hallucinations,” Salmon said.

“The same may be true of notable visual perceptual deficits picked up by the FLT, but further research is needed to answer that question,” he added.

Salmon noted that although the findings are promising, the study was small and not reflective of real-world clinical settings.

“A larger study with a clinic-based population is needed to determine how various co-morbidities might impact the efficacy and utility of the FLT in the clinic setting,” he said.

The study was funded by the National Institutes of Health. Salmon is a paid consultant for Aptinyx and Biogen. Disclosures for the other investigators are listed in the full article.

Neurology. Published online August 26, 2022. Abstract

Kelli Whitlock Burton is a reporter for Medscape Medical News who covers psychiatry and neurology.

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