The degenerative processes behind Alzheimer's disease have been found to begin 10, or even 20 years before dementia symptoms become evident and the condition is diagnosed. A new study suggests that increasing symptoms of anxiety could be an early indicator of Alzheimer's, allowing physicians better targets for early interventions to treat the condition before it causes too much irreversible neurological damage.

One of the big challenges in successfully treating sufferers of Alzheimer's, and other neurodegenerative diseases, is that significant neurological damage is already done by the time clinical symptoms are clear enough to diagnose the condition. In the case of Alzheimer's disease, this preclinical phase can last over a decade before a mild cognitive impairment even becomes apparent.

The most general preclinical sign of Alzheimer's is known to be depression, so a team at Brigham and Women's Hospital set out to explore the relationship between the build-up of amyloid beta in the brain and specific symptoms of depression.

"Rather than just looking at depression as a total score, we looked at specific symptoms such as anxiety," explains first author on the study, Nancy Donovan. "When compared to other symptoms of depression such as sadness or loss of interest, anxiety symptoms increased over time in those with higher amyloid beta levels in the brain."

The study followed 270 cognitively healthy senior citizens aged between 62 and 90 years old. Over a span of five years these subjects underwent positron emission tomography (PET) scans to measure cortical levels of amyloid beta. These observations were complemented by annual assessments examining depression symptoms across three categories: apathy-anhedonia, dysphoria, and anxiety. The results clearly pointed to a correlation between increasing anxious-depressive symptoms and higher levels of amyloid beta in the brain.

"This suggests that anxiety symptoms could be a manifestation of Alzheimer's disease prior to the onset of cognitive impairment," says Donovan. "If further research substantiates anxiety as an early indicator, it would be important for not only identifying people early on with the disease, but also, treating it and potentially slowing or preventing the disease process early on."

This particular study didn't go on to connect these anxious-depressive symptoms and increasing levels of amyloid beta with a subsequent onset of Alzheimer's disease, so further long-term work needs to be done to ascertain the existence of such a connection.

The study was published in The American Journal of Psychiatry.