Hallucinations and delusions

All patients with dementia, regardless of the pathology, are actually vulnerable to developing psychosis. And by psychosis, we mean a condition where a patient has really lost touch with reality and is experiencing delusions and/or hallucinations. And patients with DLB are particularly vulnerable to developing visual hallucinations. And that relates probably to the location of the pathology– which is often in the posterior part of the brain, which supports visual function– and also to the profound deficits of acetylcholine transfer in their brains. And we know that acetylcholine is very much related to visual pathways and to the experience of visual hallucinations. Now, when you have a hallucination, it’s as if you are really seeing something.

So the experience of a hallucination is exactly the same as an experience of a normal perception, except obviously there isn’t a stimulus that’s causing that perception. So when a patient is seeing a hallucination, it’s not a sort of “as if I’m seeing something” experience. I am seeing the thing. It’s absolutely real. And people who’ve got perfect cognition who experience visual hallucinations are often able to rationalise and think, well, actually there aren’t any elephants living in Croydon, or there aren’t any alligators in Camberwell. I can’t possibly be seeing an alligator under my bed or a crocodile at the end of the road or an elephant at the end of the road. Therefore, I know this isn’t right.

But if your cognition is impaired, and you’re unable to rationalise like that, it’s unsurprising that you become completely terrified. And you look under the bed, and you see a crocodile or an alligator, and you believe that there is a real alligator under your bed. And you react as if there really was. And of course, that’s completely terrifying for patients and incredibly difficult for family members because no matter what you say to the patient, they still believe that there’s an alligator under the bed, and the whole family are at risk, and it’s a terribly dangerous, frightening situation.

And even though the visual hallucinations are the things that people remember, and they’re prominent things because they’re so extraordinary, the reports that the patients make, delusions are really common in DLB. And a delusion is a false but fixed belief that you can’t possibly argue a patient out of. And quite often, they have quite bizarre content. And also quite often, they have a rather unpleasant sort of persecutory content. So a patient will become convinced that their wife, perhaps, is going to leave them or is stealing money from them or is going to harm them. And because it’s a delusion, it’s absolutely fixed. You can’t reason with the person and change it.

And again, a nightmare to live with someone who’s developed a delusion about you. Delusions that involve misidentification are not uncommon in this group. And the commonest of those would be a patient would look in the mirror and would see– so an old lady would look in the mirror and fail to recognise herself and think there’s a witch living in my house, and I can see her when I look in this mirror, and become very, very upset and agitated about that. There’s also a fairly rare kind of delusion called a Capgras delusion, when patients will become convinced that, even though someone looks exactly like a familiar figure, that familiar figure has actually been replaced by an impostor.

And I can think of some examples from my practise. A patient who attacked his wife at the breakfast table because she was opening her own post. And he said to her, well, what are you doing. You’re opening my wife’s post. And she said, well, let me tell you, I am your wife. Of course I’m opening the post. And he got so angry with her because he thought that, even though she looked like his wife, she was actually an impostor, that he attacked her. Now, I also had a patient who had this similar problem, but affecting his car.

So he went to pick up his car from the garage after it had been serviced, and he became convinced that the car that he went to pick up wasn’t actually his car and that what had happened was that the garage had obviously destroyed or lost or taken his car and replaced it with a car that was almost identical. But when he saw it, he knew it wasn’t his car. And he got incredibly angry and refused to sort of take this car and take it away.

And when I saw him in clinic, and we were discussing what had happened, I said to him, do you really think it’s likely that a garage would go to all that trouble to sort of copy your car and replace it. He said, well, it’s mystifying, doctor, because they copied it so carefully, even the cigarette burns in the back seat were in exactly the same place as in my own car. But I knew it wasn’t my car. So you can imagine how difficult it would be to live with somebody who is having those kind of beliefs that just couldn’t be reasoned with.