The paper reviewed here is ‘Visual Hallucinations in Dementia: A Prospective Community-Based Study with Autopsy’ by Debby Tsuang and colleagues and freely available here.
Aim: The aim of the study was to investigate hallucinations in people with dementia living in the community
Method: The researchers used a prospective design. They identified new cases of dementia (or established diagnoses of less than 1 year) through a number of sources
‘by reviewing specialty and primary care clinic logs, hospital records, head CT scan requests, and referrals from primary care practitioners and neurologists‘
Although just over a third of subjects with cognitive impairment declined to take part, the researchers inform us that the sample demographics were similar to the regional demographics. The researchers used the DSM-III and NINCDS-ADRDA criteria to establish diagnoses. They used the Mini-Mental state examination and the BEHAVE-AD scale to investigate psychopathology. Presumably the BEHAVE-AD was used to capture data on hallucinations. While this does examine hallucinations specifically I suspect it will underestimate prevalence particularly in cases which have occured transiently during an episode of delirium or where this might have been overlooked for various other reasons. Even so it does seem to be a reasonably good tool for this purpose. Autopsies were undertaken in those subjects that passed away. The researchers detail the staining techniques and staging that was undertaken at autopsy. T-tests were used to compare the variables although assumptions were made about the distributions although there is no mention of whether this had been verified by visual inspection. Interestingly there is no control for multiple comparisons.
There were a large number of subjects at the entry point but many were excluded due to insufficient clinical information or else insufficient tissue sampled at autopsy.
27 subjects experienced visual hallucinations
121 subjects did not experience visual hallucinations
Compared to sujects without visual hallucinations, subjects with visual hallucinations were more likely to experience
Lewy Body pathology
Alzheimer’s Disease pathology was the most common finding in those with visual hallucinations (59%)
Alzheimers’s Disease was similar in both those with and without visual hallucinations
The researchers provided a detaileddiscussion of their findings. I thought that there was a lot of interesting data in the study and that this could helpfully be considered to be an exploratory analysis. If this was the case, then in the absence of clear primary hypotheses the multiple comparisons that have taken place could be considered a secondary analysis in which case the relevant corrections would be needed. Controlling for mutliple comparisons however can be quite harsh in terms of removing significant findings. On that basis I have been quite cautious in interpreting the agitation, delusions and apathy findings. What I have found most interesting are the descriptive statistics. So reading that 59% of subjects had Alzheimer’s Disease pathology was quite helpful although even here it would also be interesting to know a little more about the relationship with delirium. Nevertheless even if all visual hallucinations occurred in the context of delirium, the neuropathological findings would suggest even there that they are comorbid with AD pathology and so this is a moot point. Certainly this study opens up the possibility of further investigations into the relationship of visual hallucinations with apathy, delusions and agitation while controlling for delirium.
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