98 Percent of People With Alzheimer's Develop This Symptom First, Study Says

Experts have long reported that the majority of dementia cases begin with mild cognitive impairment. However, research suggests that in the case of late-onset Alzheimer's disease—defined as cases in which the first symptoms appear after the age of 65—there's an additional symptom that's missing from this picture.

According to a 2017 study published in the journal BMJ Open, depression occurs as a first symptom of late-onset Alzheimer's with nearly the exact same frequency as cognitive impairment—a fact which distinguishes it from early-onset cases of the condition. "We found that depression and cognitive impairment were the first symptoms to appear in 98.5 percent and 99.1 percent of individuals in a study with late-onset AD (LOAD) and 9 percent and 80 percent, respectively, in early-onset AD (EOAD)," the team wrote.

This data suggests that depression occurs as a compounding first symptom in the vast majority of late-onset cases of Alzheimer's, while being relatively rare as a first symptom in early-onset cases. This is especially relevant, given that the National Institute on Aging estimates that 90 percent of Alzheimer's cases are considered late-onset.

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