Depression and dementia may both present with cognitive dysfunction (e.g., memory loss and slowed information processing speed) and emotional distress; therefore, it may be difficult for the patient and family members to distinguish between the two. A clinician can utilize a detailed clinical interview and neuropsychological assessment to delineate these processes. For example, individuals suffering from depression would have had depressive symptoms before the onset of cognitive difficulties, whereas individuals with dementia may have developed mood disturbances after experiencing cognitive decline (1).
In terms of the neuropsychological test results, people with depression generally perform better than those with dementia on these cognitive tests. Individuals with depression may have difficulties with retrieving information but show evidence of retention when given cues (i.e., recognition memory). Individuals with dementia, on the other hand, may lose the information and cannot recall it even with prompts. Individuals with depression may also perform better on more difficult tasks relative to easier ones, while people with dementia demonstrate more impairments on harder measures. Generally, a “depression profile” may comprise of mild attention, executive functions (higher-order cognitive abilities such as problem-solving and performing tasks quickly), and memory retrieval weaknesses, while “dementia profiles” may encompass more global and severe difficulties with memory retention and retrieval, language, visuospatial abilities, as well as attention and reasoning and executive functions.
In a meta-analysis of 16 studies with 89 effect sizes, the researchers found that certain memory measures were more useful in distinguishing depression from dementia (2). These measures included information retrieval after a delay (relative to without a delay), those with a distraction after stimulus onset, more difficult tests, and tasks involving words and common objects (instead of ones involving numbers, sentences, and geometric designs) (2). However, different types of dementias would yield different kinds of profiles. For instance, individuals with vascular dementia may have the same difficulties as individuals with depression as outlined above. Thus, it is up to the clinician to synthesize the reported symptoms, neuropsychological test results, and neuroimaging studies to arrive at the accurate diagnosis.
Additionally, depression and dementia are not mutually exclusive conditions. There is a strong link between depression and all types of dementia. Depressive symptomology is prevalent among people with dementia. Risks for depression and dementia are elevated in older age. Major depression occurs in 3.2% of individuals with Alzheimer’s disease (AD) and 21.2% of individuals with vascular dementia (3). These depressive symptoms may either represent a reaction to cognitive difficulties or product of the neurodegenerative processes. Sometimes, depression may present as a first sign of dementia, particularly in cases of vascular dementia.
The exact mechanism that mediates this correlation is not yet known, but several hypotheses have been proposed in the literature. It is possible that not one, but multiple of these explanations may account for the relationship between depression and dementia, depending on the type of dementia and individual differences. Depression may be a risk factor for dementia. Earlier-life depression is found to have a two-fold increase in risk of developing dementia, and late-life depression is associated with a two to five-fold increase in risk (4). The combination of depression and other risk factors for dementia, such as cardiac conditions, hypertension, and diabetes, may increase one’s risk. In a large population-based study, the combination of depression and diabetes led to greater odds of developing dementia than the added effects of their individual risks. This pattern was seen in both AD and vascular dementia but was stronger for the latter (5).
Depression and dementia may share underlying pathologies. Both lesions in connections between brain cells (more characteristic of a vascular process) and atrophy or brain cell loss in the temporal lobe (prominent changes associated with AD) are shown to precede and independently predict the development of depression and dementia (6). Further, it has been demonstrated that chronic depression accelerates atrophy in the frontal lobe and anterior cingulate of the brain and lead to earlier conversion from mild cognitive impairment (MCI; the transition stage between normal cognition and dementia) to AD (7). A systematic review by Byers & Yaffe (4) summarized the likely biological mechanisms underlying the link between depression and dementia, including vascular disease, changes in glucocorticoid steroids and hippocampal atrophy, increased β-amyloid plaque burden, inflammatory processes, and deficits of nerve growth factors.
Although the exact basis for the interaction between depression and dementia is equivocal, the association between the two is strong. Therefore, monitoring of cognitive status throughout the neuropsychological assessment is important for individuals with depression. Further, treatment of modifiable factors, such as depression, may help to reduce the risk of dementia. Although intervention studies have varied in results regarding the cognitive effects of treating depression in the geriatric population (4), there is some evidence that successful treatment of depression and diabetes combined with a healthy diet can lead to as much as a 20% decrease in risk of developing dementia (8).
Dr. Thomas has been working with patients in the early stages of dementia with neurofeedback and there have been successful results. A chapter reviewing the small literature of neurofeedback helping to pull people out of dementia was authored by Dr. Thomas (10). Depression can also be treated with neurofeedback successfully.
— M Chen & J. L. Thomas
References
1.The Mayo Clinic. Alzheimer’s or depression: Could it be both? Retrieved from https://www.mayoclinic.org/diseases-conditions/alzheimers-disease/in-depth/alzheimers/art-20048362.
2.Lachner, G, & Engel, R (1994). Differentiation of dementia and depression by memory tests: A meta-analysis. Journal of Nervous and Mental Disease, 182(1): 34-29.
3.Newman, S (1999). The prevalence of depression in Alzheimer’s disease and vascular dementia in a population sample. Journal of affective disorders, 52(1), 169-176.
4.Byers, A, & Yaffe, K (2011). Depression and risk of developing dementia. Nature Reviews Neurology, 7(6), 323-331.
5.Katon, W, Pedersen, H, Ribe, A, Fenger-Grøn, M, Davydow, D, Waldorff, F, & Vestergaard, M (2015). Effect of depression and diabetes mellitus on the risk for dementia: a national population-based cohort study. JAMA psychiatry, 72(6), 612-619.
6.Gudmundsson, P, Olesen, P, Simoni, M, Pantoni, L, Östling, S, Kern, S, & Skoog, I (2015). White matter lesions and temporal lobe atrophy related to incidence of both dementia and major depression in 70‐year‐olds followed over 10 years. European journal of neurology, 22(5), 781.
7.Sacuiu, S, Insel, P, Mueller, S, Tosun, D, Mattsson, N, Jack, C, & Mackin, R (2016). Chronic depressive symptomatology in mild cognitive impairment is associated with frontal atrophy rate which hastens conversion to Alzheimer dementia. The American Journal of Geriatric Psychiatry, 24(2), 126-135.
8.Ritchie, K, Carriere, I, Ritchie, C, Berr, C, Artero, S, & Ancelin, M (2010). Designing prevention programmes to reduce incidence of dementia: prospective cohort study of modifiable risk factors. Bmj, 341, c3885.
9.Prichep, L et al. (2006).Prediction of longitudinal cognitive decline in normal elderly with subjective complaints using electrophysiological imaging. Neurobiology of aging, 27, 471-481.
10. Thomas, J (2011) Brian brightening: Neurotherapy for enhancing cognition in the elderly. In P. Hartman-Stein and A LaRue (Eds) Enhancing cognitive fitness in adults.. NY: Springer, pp 433-444.
