Age at Alzheimer’s disease onset may depend on history of psychiatric conditions

Psychiatric conditions were associated with a younger age at onset of Alzheimer’s disease, and age differences only grew with each additional psychiatric diagnosis, researchers reported.

“Depression has been identified as a modifiable risk factor associated with Alzheimer’s disease (AD),” Zachary Miller, MD, an assistant professor and behavioral neurologist at the Memory and Aging Center at the University of California, San Francisco, told Healio Primary Care. “Less attention has been focused on the association between Alzheimer’s with other psychiatric diseases including anxiety, PTSD, schizophrenia and bipolar disease.”

The researchers screened 1,500 patients with AD at the UCSF Memory and Aging Center for a history of those psychiatric conditions.

Miller and colleagues reported that 43.3% of the patients had a history of depression, 32.3% had a history of anxiety, 1.2% had a history of bipolar disorder, 1% had a history of PTSD and 0.4% had a history of schizophrenia. Patients with depression were 2.1 years younger at the age of AD onset, and those with anxiety were 3 years younger at the age of AD onset (P < .001).

The researchers reported that the presence of only one psychiatric disorder was associated a 1.5-year younger age at AD onset; history of two psychiatric conditions was associated with a 3.3-year younger age at AD onset; and three or more diagnoses was associated with a 7.3-year younger age at AD onset (P < .001).

The differences in age at AD onset suggest that each psychiatric diagnosis “possesses unique and additive effects on AD pathophysiology,” the researchers said.

The results also showed that patients with depression and anxiety were more likely to be women and had fewer typical AD risk factors. The prevalence of autoimmune disease was significantly higher among patients with depression (P = .01), and patients with anxiety had a greater frequency of seizures (P = .002).

Given the associations with autoimmune disease and seizures, “the presence of depression might reflect a greater burden of neuroinflammation and anxiety a greater degree of hyperexcitability,” according to the researchers.

Miller said that “optimizing the care of psychiatric disease may pose the additional benefit of dementia prevention.” He encouraged primary care physicians to refer patients with psychiatric symptoms that are “complex and refractory towards first-line therapies” to a psychiatrist or psychologist.

“We always advocate for the regular monitoring of cognition in aging populations, and in light of the findings in our study, individuals with a greater degree of psychiatric disease may benefit from even closer monitoring,” he said. “Should PCPs and/or mental health professionals detect concerns in cognition, referral to behavioral neurology would be most appropriate.”