A nationwide case-control study conducted by researchers from the University of Eastern Finland found an association between mental and behavioral disorders and Alzheimer’s disease (AD). However, this effect was dependent on the time between the first signs of psychiatric disorders and the diagnosis of Alzheimer’s.
The study, “Hospital-treated mental and behavioral disorders and risk of Alzheimer’s disease: A nationwide nested case-control study,” was published in the journal of the European Psychiatric Association (EPA), European Psychiatry.
Previous studies have tried to understand whether psychiatric disorders could be associated with Alzheimer’s development and progression. However, the use of different methodologies has generated mixed results and inconsistent findings.
“Identification of potential AD/dementia risk factors is important, because it may aid in targeting or developing potential strategies to prevent or delay the dementia onset,” the researchers wrote.
The study was based on the Finnish Medication and Alzheimer’s disease (MEDALZ) study, which includes all 70,719 community-dwelling residents of Finland who were diagnosed with Alzheimer’s between 2005 and 2011. The authors compared the clinical history of psychiatric disorders, extracted from the Finnish Hospital Discharge Register, of 1,932 Alzheimer’s patients and compared them to those of 1,784 age- and gender-matched controls.
The authors found that a history of mood disorder, such as depression, or a behavioral disorder was associated with an increased risk of Alzheimer’s. However this association was only significant if the psychiatric symptoms were reported within five years of the AD diagnosis. An extension of the time windows between exposure and Alzheimer’s disease outcome to 10 years showed that these factors would no longer represent a risk for AD.
The authors also observed an increasing incidence of psychiatric disorders before a diagnosis of AD. These results taken together suggest that indeed mental and behavioral disorders might play a role in the development of Alzheimer’s disease.
“[These results] underline the importance of proper differential diagnostics of AD and mental and behavioral disorders,” the researchers wrote.
Although no relationship was found in this study between a history of psychiatric disorders 10 to 40 years before Alzheimer’s diagnosis, it is still important to note that these patients have a poorer outcome with decreased life expectancy.
In addition, this study showed the importance of the use of an appropriate time window when assessing the risk factors of neurodegenerative diseases with a long onset period such as Alzheimer’s disease, which otherwise may induce the identification of false risk factors for Alzheimer’s.