A Bedside Test to Differentiate Dementias?

Andrew N. Wilner, MD


April 24, 2018


While attending the American Academy of Neurology meeting in Los Angeles, California, Medscape contributor Dr Andrew Wilner interviewed University of Tennessee neurology resident Dr Aman Deep about his research into differentiating Parkinson disease (PD) and Alzheimer disease (AD) dementia.

Wilner: Tell us about your new study, Dr Deep.

Deep: What led us to do this study[1] was kind of an accidental finding in the clinic. My boss, Dr Abraham Lieberman, did a study in which they looked at patients with PD and essential tremor; so these were patients with PD without dementia. They had a drifting of the arm, either upwards or laterally. But in this group there were a few patients with mild to moderate dementia with a mini-mental status exam (MMSE) of 26 or more. So they were only mildly demented, but these patients had a mild downward drift when you put out their arm.

This led us to ask, "Why don't we look at patients with moderate to severe dementia and see how they react?" As a result, in the new study we looked at 56 patients with PD dementia and an MMSE score of less than 24. We asked the patients to point fingers from both hands at a mark on a ruler and hold it there for 15 seconds. The point was that if they have any motor weakness, their fingers will drift downward.

After 15 seconds, we asked the patients to close their eyes and we observed them for the next 15 seconds. Out of 56 patients, 53 had bilateral downward drift of more than 5 cm. The other three patients also had drift, of less than 5 cm.

So we thought, do these results have something to do with PD plus dementia, or dementia alone? To determine this, we looked at 35 patients with AD dementia. Out of 35 patients, only one patient had downward drift, and it was less than 1 cm.

Wilner: It's interesting, because demented patients often perseverate. You ask them to hold their arm out and then you come back in the room 10 minutes later and they're still holding their arm out. It sounds like the AD patients had no trouble following the instructions, but the PD patients had another phenomenon: motor impersistence. With their eyes closed their arms tended to drift down.

Deep: Right. And I should point out that none of these patients had proprioceptive loss. So we can't say that they don't know the positions of their joints. And we didn't know why our findings were happening. We did a literature search, and around 1930, a scientist named Dr Martin reported a similar phenomenon in patients with postencephalitis PD. In that case, he would ask a patient to touch their shoulder. With their eyes open they would do it perfectly. But when he asked them to close their eyes, they had downward drift. And he couldn't figure out the reason behind this either.

There was one paper that looked at the difference between PD dementia and AD dementia in terms of memory and IQ. They found that like patients with AD dementia, the PD patients' symptoms were due to reduced acetylcholinesterase activity in the brain.

So I think it's rehypothesizing that these patients tend to forget where they're supposed to keep their hand.

Wilner: It sounds to me like it's almost an attention deficit. They're not sustaining their attention and are getting tired of the test, and the arm goes down.

Deep: Right. And another thing is that the drift in these patients was related to the mini-mental score. The worse the score, the more the drift.

Wilner: So would this be a useful bedside test to differentiate patients with AD dementia and those with PD dementia?

Deep: That's what we're hoping, yes. And we're also hoping that it can help gauge the severity of dementia in PD patients. The future plan is to look at an increased number of patients to increase the power, and also compare our patients with the general population as well as with PD patients without dementia.


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