Alzheimer’s disease is the most common cause of dementia, a condition that slowly damages memory, thinking ability, and daily functioning.
Millions of people around the world live with Alzheimer’s, and the number is expected to grow as populations age. While Alzheimer’s is often studied on its own, scientists are increasingly discovering that many patients actually have more than one brain disorder at the same time.
One of these additional conditions is called frontotemporal lobar degeneration, often shortened to FTLD. FTLD is another type of neurodegenerative disease that affects the brain, but it usually damages different areas than Alzheimer’s does.
It can lead to major changes in personality, behavior, and emotional control. For many years, doctors could only confirm the presence of FTLD after a person had died, during an examination of brain tissue in an autopsy.
Now new research suggests that doctors may be able to identify people who have both Alzheimer’s disease and FTLD while they are still alive. The study, published in the medical journal Neurology, shows that certain mental and behavioral symptoms may offer clues that both diseases are present.
The research was led by Daliah Ross, a postdoctoral fellow in the clinical neuropsychology program at Brown University’s Warren Alpert Medical School. Ross and her colleagues wanted to understand how having two neurodegenerative diseases at once might affect a patient’s symptoms.
Scientists have long known that Alzheimer’s disease mainly affects memory and thinking abilities. In contrast, FTLD tends to affect personality, emotions, and social behavior. People with FTLD may show symptoms such as impulsive actions, loss of social awareness, or dramatic personality changes.
Ross noticed that most research studies examine brain disorders separately, even though many patients actually have more than one condition.
According to Ross, people with neurodegenerative diseases often have Alzheimer’s along with another brain disorder. Despite this, scientists have done relatively little research on how these diseases interact with each other.
To investigate the issue, the researchers examined data from 29 Alzheimer’s Disease Research Centers across the United States.
These centers collect long-term information about patients who are studied during life and whose brains are examined after death. This allows researchers to compare symptoms observed during life with the actual disease found in the brain.
The study focused on 919 people whose brain tissue had been examined after death and showed signs of Alzheimer’s disease, FTLD, or both conditions. By studying these records, the researchers were able to compare the symptoms experienced by patients in each group.
The results revealed clear differences between patients who had only one disease and those who had both. Compared with people who had FTLD alone, patients who had both Alzheimer’s disease and FTLD were more likely to have experienced anxiety, delusions, and irritability before their death.
On the other hand, when researchers compared the mixed group with patients who had only Alzheimer’s disease, they found different patterns. People with both conditions were more likely to show personality changes and disinhibition. Disinhibition means a person may act in socially inappropriate ways or lose their usual self-control.
These findings suggest that when both diseases occur together, the combination creates a unique set of symptoms that includes features of both disorders. Recognizing this pattern may help doctors identify patients with mixed brain disease earlier.
Ross explained that neuropsychiatric symptoms, which include emotional and behavioral changes, can have a major impact on patients and their families. Symptoms such as irritability, anxiety, or personality changes can affect relationships, caregiving needs, and quality of life.
If doctors can better recognize when both Alzheimer’s disease and FTLD are present, patients and caregivers may receive clearer information about what to expect. This can help families prepare for future challenges and make more informed care decisions.
Dr. Edward Huey, a co-author of the study and associate director of Brown’s Center for Alzheimer’s Disease Research, said the findings also strengthen the link between certain symptoms and FTLD. Personality changes, apathy, and socially inappropriate behaviors are particularly common in FTLD but less typical in Alzheimer’s disease alone.
Currently, there are treatments that can help manage some symptoms of Alzheimer’s disease, and new disease-modifying therapies are being developed. However, there are still no treatments that directly slow or stop FTLD. Because of this, understanding when FTLD is present alongside Alzheimer’s disease is especially important.
The study also highlights an important challenge in modern dementia research. As new treatments for Alzheimer’s disease become available, scientists must understand how these therapies work in patients who have multiple brain disorders at the same time.
For example, a drug that targets Alzheimer’s disease might not fully address symptoms caused by FTLD. Without recognizing the presence of both diseases, doctors might have difficulty explaining why certain treatments do not work as expected.
Overall, the research shows that studying mixed forms of dementia may be just as important as studying single diseases. Many patients do not fit neatly into one category, and their symptoms may reflect a combination of brain conditions.
This study provides valuable evidence that behavioral and psychological symptoms can offer clues about these hidden combinations of disease. While more research is needed, the findings may help clinicians improve diagnosis, counseling, and care planning for people living with complex forms of dementia.
A key strength of the research is the large dataset collected from many Alzheimer’s research centers. However, the study also has limitations.
Because the diagnoses were confirmed only after death, doctors still need better tools to identify these conditions during life. Future research may combine behavioral observations with brain scans and biological markers to improve early detection.
Despite these limitations, the study moves the field forward by showing that mixed brain diseases may leave recognizable patterns in a patient’s symptoms. This insight could help doctors better understand why dementia affects people in different ways and provide more personalized care for patients and their families.
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The study was published in the journal Neurology.
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