Dr Shock MD PhD: Differences between depression and dementia

We have an elderly patient admitted to our ward for second opinion. She has a history of depressive episodes. Two post partum depressions and one depressive episode about 6 years ago. She is 72 years old.

When I met her the first day she was in a dysphoric mood complaining about her transfer to our department. She already took nortryptiline for 2 months with adequate plasma levels. Her referring psychiatrist said that this had led to some improvement, the patient was less pleased with the antidepressant. According to her this drug was causing memory problems.

She demanded ECT since that was the reason for her transfer.

During the observation period she had depressive symptoms as well as cognitive symptoms.

Dementia and depression are frequently comorbid among older adult patients.Depression is related to cognitive
decrement and can even represent the first signs of a neurodegenerative process.It can be difficult to distinguish
depressed patients exhibiting the first signs of dementia from those whose cognition will improve with treatment.

How can we differentiate between depression and dementia?

Neuropsychological assessment is generally considered the gold standard in differentiating between depression and the early stages of dementia.
- Cognitive impairments in dementia are usually more severe than in patients with depression.
- Patients with depression will do more poorly on tasks that require more effort to complete a task. Patients with dementia score low on tests because of ability-based deficits rather than on the amount of effort needed for the test.
- Patients with depression generally retain the learned information during testing, patients with dementia show a higher rate of forgetting of initially recalled material over time. Besides these retrieval deficits in patients with dementia, memory consolidation is also worse compared to depressed patients as shown with recognition memory tasks.
- Patients with beginning dementia exhibit greater false-positive scores whereas depressed patients usually stay on the save side and produce more false negative errors. Patients with dementia show specific impairments such as practical shortcomings, difficulty with temporal relationships between events.
It is not clear which depressed elderly is predisposed to develop dementia from those depressed elderly that will not. It is suggested from the literature on this subject that depressed patients exhibiting early decrements on tasks of recall memory, visuospatial skills (Visuospatial skills allow us to visually perceive objects and the spatial relationships among objects.), and executive functions may be at greater risk for developing dementia than patients without such a degree of decrement.

The depression symptoms that might predict development of dementia are:
- Apathy during a depressive episode, which is disinterest, low energy, and concentration difficulties is a risk factor for developing dementia later on as shown by a 3-year longitudinal study.
- Apathy is also positively associated with dementia severity, dysphoria has a negative relationship.
- Fewer affective symptoms such as feelings of guild, depressed mood, suicidal ideation, and more agitation and motor slowing are positively associated with dementia.
- Late onset depression, that is a first depressive episode at a later age, is a risk factor for dementia than for early onset depressive disorder.
The presence of white matter and subcortical gray matter hyperintensities in imaging studies are positively related with depression during old age. The boundary between vascular dementia and Alzheimer dementia is less clear than once hypothesized. Patients with hypertension have increased amounts of senile plaques and neurofibrilllary tangles and previous high cholesterol is positively associated with Alzheimer disease. At least a part of the relationship between geriatric depression and dementia can be explained by a vascular compromise to the frontostriatal circuit.

Dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis is represented by high levels of glucocorticoids during depression. In depressed patients with hypercortisolemia cognitive deficits have been demonstrated together with lowerded hippocampal formation volume and reduced metabolism. There is a possibilty that hippocampal atrophy associated with HPA dysfunction in depression might be a risk factor for developing dementia later on.

Depression as a prodrome of dementia. In a subset of older adults depression can represent the first symptoms of dementia even when accounting for cognitive complaints. It is unknown whether vascular compromise of the frontostriatal regions, structural damage by cortisol dysregulation or both account for this relationship.

Depression as a risk factor for dementia. Due to lack of good prospective longitudinal studies this relationship remains to be seen.

Where does this leave our elderly patient?
Her dysphoric mood and prior history of depressive episodes (no late onset) makes me more optimistic about her cognitive symptoms. Neuropsychological testing is our first goal although her depression might be to severe for a reasonable test outcome.I'll keep you posted.

Based on:

Wright, S.L., Persad, C. (2007). Distinguishing Between Depression and Dementia in Older Persons: Neuropsychological and Neuropathological Correlates. Journal of Geriatric Psychiatry and Neurology, 20(4), 189-198. DOI: 10.1177/0891988707308801