Ask the BCAT Faculty: Do People with Schizophrenia Develop Alzheimer's?
I am a psychiatrist working in Boston, and I recently attended a seminar at our hospital. The instructor said that if people with schizophrenia live long enough, they invariably develop Alzheimer’s disease. We were told that both schizophrenia and Alzheimer’s share a common molecular background. However, in my training, I learned that the clinical presentations of the diseases are quite different. This has been my personal experience with patients. Can you shed some light on this issue? If you have schizophrenia, will you develop Alzheimer’s disease?
BCAT Faculty Response:
Thank you for your email, David. You ask a very good question, one that researchers have devoted quite a bit of attention to over the past fifteen years. Our understanding is not as clear as we would like, but evidence is emerging to provide some insight. Cognitive impairment is a key clinical feature of both schizophrenia and Alzheimer’s disease. In both disorders, cognitive deficits can be seen in verbal memory, abstract thinking, executive functions, sustained attention, and response inhibition. It is important to note that while a majority of people with schizophrenia develop the disorder in their late teens or early adulthood, others develop it later; late-onset or very late-onset schizophrenia can occur after age 60. Cognitive impairment may be more pronounced in the later onset cases than in early onset ones. Studies show that more than 25% of older adults with schizophrenia have moderate to severe cognitive impairment.
It is true that a significant number of people with schizophrenia have or will develop dementia, but it is unlikely that it is of the Alzheimer’s type. Post-mortem schizophrenia studies have not found an increased incidence in Alzheimer’s disease pathology. That is, the characteristic Alzheimer’s’ plaques and tangles are not consistently present in the brains of people with schizophrenia.
There are two other points to consider. First, the development of cognitive impairment in schizophrenia is distinct from the typical course of Alzheimer’s disease. Many studies have found cognitive impairment in schizophrenia to be relatively static. This is, of course, quite different from what one expects in Alzheimer’s disease, in which cognitive functioning declines gradually. It should be pointed out that other studies have found decline to be progressive but not necessarily fitting a typical Alzheimer’s pattern. Second, life expectancy of people with schizophrenia is much lower than life expectancy of people with Alzheimer’s. Recent longevity data suggests that most people with schizophrenia do not live past 70. Contrast this with Alzheimer’s disease, in which early symptoms generally do not emerge until the 70s. Generally, different symptom onset patterns indicate different diseases.
In our view, the vast majority of people with schizophrenia, regardless of time of onset, have cognitive impairment. Many will meet criteria for dementia, with or without progressive cognitive deficits. However, it is unlikely that the type of dementia is actually Alzheimer’s.
We hope you found this response helpful, and encourage more questions for the BCAT faculty.