Late-life depression is often accompanied by cognitive impairment, with studies suggesting that combined depression and cognitive dysfunction is present in roughly 25% of older adults. The number of community residents with both depressive symptoms and impaired cognition doubles every five years after the age of 70.
In some cases, depression and cognitive impairment may be related to the same underlying disorder, while in others, they may coexist independently. Differential diagnosis and treatment decisions can be complicated by various factors.
Cognitive Impairments in Depression
Neuropsychological impairments spanning many cognitive domains, including episodic memory, visuospatial skills, verbal fluency, and psychomotor speed, have been consistently reported in late-life depression. These impairments, particularly memory impairment, have been attributed to dysfunction in subcortical structures related to mood regulation.
Deficits in executive function are also common, occurring in nearly 40% of elderly depressed patients. It has shown to have a negative effect on clinical outcomes.
Depression in Dementing Disorders
Estimates of the rates of depression in dementing disorders range from 30 to 50%, with major depression or clinically significant depressive symptoms found in 17 to 40% of Alzheimer’s disease (AD) patients. Depression in AD is notable for prominent disturbances in initiation, motivation, and apathy.
Patients with subcortical dementias, including vascular dementia and Parkinson’s disease (PD), are more likely to experience depression than those with AD, with rates in PD reaching 50%.
Depression as a Prodrome
In some cases, a first episode of depression presenting in late life may be a prodrome of a dementing disorder. Depressive symptoms have been associated with an increased risk of incident dementia.
The patients with subthreshold cognitive symptoms and concurrent depressive symptoms are more likely to progress to dementia. However, recent data suggest that there is a significant decline in functioning that precedes late-onset depressive symptoms in AD, and cognition declines subsequently.
Declining Depression Rates
The prevalence of depressive symptoms decreases as AD progresses. Patients exhibit fewer mood-related symptoms but increased agitation and psychomotor slowing.
The rates of depression in AD patients remain stable for roughly the first three years of follow-up but decline by as much as 30% in the fifth year of follow-up.
Depression as a Risk Factor
Studies examining the link between geriatric depression and subsequent dementia have shown conflicting results. Some meta-analyses showed an increased risk for the development of AD in patients with a history of depression.
While others found this association only when depressive symptoms appeared within 10 years prior to dementia onset. The increased risk for dementia may be conferred by factors such as severity, age of onset, or number and length of depressive episodes.
Depression with Reversible Dementia
Some older adults with late-life depression may exhibit a reversible dementia syndrome, characterized by cognitive impairment that mimics dementia but diminishes upon remission of depression. These patients usually have severe, late-onset depression but mild dementia syndrome.
They exhibit more psychic and somatic anxiety, early morning awakening, and loss of libido compared to AD patients with concomitant depression. However, a large percentage of these patients progress to irreversible dementia within 2-3 years.
Executive Function and Treatment Response
Abnormal performance on tests of executive functioning, such as the Initiation/Perseveration subscale of the Dementia Rating Scale and the Stroop Color Word test, predicts adverse clinical outcomes in geriatric depression.
It includes poor and slow antidepressant response, relapse, and higher levels of functional disability. Specific executive functions, such as semantic strategy, have been found to predict remission during antidepressant treatment, explaining performance differences between remitters and non-remitters.
Prognosis of Cognitive Impairment
Mild cognitive impairment during depressive episodes in late life does not typically progress to dementia and is often a stable disturbance that improves moderately when depressive symptoms are ameliorated. However, follow-up studies suggest that geriatric patients with depression and more severe cognitive symptoms.
Some of them like ‘reversible dementia,’ are at an increased risk for developing irreversible dementia, with 9-25% of these patients developing irreversible dementia each year.
Pharmacologic Treatment
The Expert Consensus Guideline recommends antidepressant drug therapy combined with a psychosocial intervention as the treatment of choice for geriatric depression. While tricyclic antidepressants may worsen cognitive function, some SSRIs, such as sertraline and citalopram, have been shown to improve cognitive function.
However, citalopram may worsen verbal learning and processing speed in patients who remain depressed despite treatment. The Expert Consensus Guideline recommends antidepressant drug therapy combined with a psychosocial intervention as the treatment of choice for geriatric depression.
