Depression and dementia

Depression and dementia are common syndromes in older people and are usually managed by general practitioners. Comorbidity compounds the impact on patients, carers and health services.1-3 Yet, the relationship between the two is complex — features overlap and each seems to be a possible risk factor, symptom or consequence of the other. Thus, identification and effective management of depression in people with dementia remains a challenging task in clinical practice.

This article provides a clinically oriented selective review of current knowledge about depression in dementia, specifically aimed at primary care practitioners. Practice pearls are provided (Box 1). Although the literature overwhelmingly focuses on Alzheimer disease, here we also discuss mild cognitive impairment and other types of dementia. Mild cognitive impairment refers to a clinical status where a patient performs below norms on cognitive tests but does not have dementia. Either the patient or someone who knows him or her well should have noticed a change from premorbid cognitive function. Statistically, people with mild cognitive impairment are at increased risk of developing dementia over time, although the individual risk can vary significantly.4

Reported rates of depression in dementia vary substantially, depending on the population sampled, means of assessment and definition of caseness. Overall, most well conducted population-based studies report prevalences between 8% and 30%.1,5,6 In hospitalised patients and nursing home residents, the prevalence may be over 40%.1,5 Variance in prevalence estimates is greater in studies of mild cognitive impairment.6 A recent review of depression in mild cognitive impairment found median proportions of 44% in samples of hospital-based patients and 16% in community-based samples.1 The limited studies investigating depression in people with vascular dementia, Lewy body dementia or dementia associated with Parkinson disease suggest that depression may be more common in these syndromes than in Alzheimer disease.1

Reported risk factors include female sex, earlier age at dementia onset,7 a past history of depression or emotional problems,7,8 and recent losses.8 There is some evidence that, contrary to conventional wisdom, stage of dementia and insight into the diagnosis have little impact on depression rates.1,9

The consequences of depression in people with dementia include increased burden on patients and caregivers,10 increased caregiver depression,10 exacerbation of cognitive and functional decline,3,11,12 more dementia-related behavioural disturbance,13 poor outcomes from other medical or surgical interventions,3,14 earlier admission to nursing homes, and increased mortality.12,15-17

There is substantial academic interest in the relationship between depression and dementia, particularly regarding the direction of causality and possible disease mechanisms. There is now reasonable evidence that a history of depression is a risk factor for developing dementia, particularly when the depression occurs early in life or is severe.18 Conversely, incident depression occurring temporally close to the onset of cognitive impairment may represent very early or prodromal symptoms of dementia itself.1,19-21

A neuropathological mechanism common to both conditions, such as cerebrovascular disease or hippocampal atrophy, has been suggested.22-26 However, as with most psychiatric illness, the literature does not consistently support any “neat” pathophysiological hypothesis. It is likely that a complex intertwining of multiple factors is variably involved in different individuals.

Depression in people with dementia remains underdiagnosed, particularly in residential care settings.27,28 Disease, patient, clinician, family and system-level factors may all hinder accurate assessment.

Depression may present differently in people with comorbid dementia, particularly when the dementia is advanced. Although typical major depressive disorder (MDD) is seen, the clinical picture often lacks prominent sadness, hopelessness and guilt and is, overall, less severe.29 Anxiety, psychomotor retardation, loss of energy or appetite, anhedonia, irritability, delusions and hallucinations may all be more common (and prominent) than in people without dementia. These symptoms can also be part of the dementia itself or suggest delirium.3,24,30 Unexpected or rapid change in mood, cognitive deterioration, or increased behavioural and psychological symptoms of dementia (eg, disinhibition, agitation, anxiety or aggression) may be the only indicators of superimposed depression.13

Conventional techniques and instruments for assessing depression may not be reliable or practicable in people with dementia. When obtaining a patient history, patients may underreport, and their carers overreport, symptoms of depression.10 As dementia advances, cognitive and communication difficulties may also hamper assessment of the intrapsychic symptoms of depression, including subjective mood states, thoughts about oneself or others, and general outlook for the future. The use of standardised questionnaires is helpful only if they are validated in this population, which is not the case for many of the common depression rating scales.31

A useful scale is the Cornell Scale for Depression in Dementia (CSDD; Box 2).32 There are also modified Diagnostic and statistical manual of mental disorders, 4th edition (DSM-IV) criteria for MDD that include the diagnosis of Alzheimer disease.33 In Australia, the CSDD is incorporated into the Aged Care Funding Instrument, which is used to determine the funding allocated to aged care facilities for individual residents. However, due to limited time and staff in such facilities, attention to completing the CSDD is often cursory, and the results rarely alter management for individual residents. Moreover, serial evaluations are uncommon.28 Regularly combining use of rating scales with a thorough history would improve detection rates.

Obtaining as much history as possible regarding mood and behavioural symptoms from the patient and carers, such as family or residential care staff, is essential, particularly when communication difficulties are evident. This should be repeated at regular intervals (eg, 6-monthly) or if there is any evidence of a significant change in behaviour.28,34,35 It is important to enquire about a past history of depression and past treatments for depression, as well as family history, medical history, and drug and alcohol history. Physical illnesses, prescription medications, functional disability, social isolation, life stressors, bereavement and other losses are also important, as they may increase vulnerability to depression.1,29

Where there is clinical suspicion of depression (eg, change in mood or any difficult-to-explain change in behaviour), definitive treatment is usually worthwhile, especially when communication difficulties due to dementia act as a barrier to obtaining a detailed history.

Management of a patient with depression and dementia should encompass biological, psychological, social, cultural and spiritual factors, particularly those that may have precipitated or may be perpetuating the depression.

A focused physical examination and investigations are essential to exclude any treatable medical cause for low mood. Such causes are more likely to be present in older people and may include physical illness and prescription medications. Common medical causes of depressed mood are listed in Box 3, and important screening investigations for an organic cause are listed in Box 4. Patients also frequently present with physical illness and depressed mood where there is a known association, but it is neither causal nor reversible (eg, depression and ischaemic heart disease). Overall physical health should be reviewed and optimised, and the depression should be specifically treated. Addressing vascular risk factors is particularly important.

Risks associated with depression in people with dementia must be considered throughout, as they may determine the type, location and urgency of treatment. Every patient with depression should be asked directly but sensitively about suicidal thoughts, plans and intent (Box 5). Suicide risk also depends on available protective supports, supervision and the patient’s access to means. Other risks include harm to others or to relationships due to agitation, aggression or irritability; loss of accommodation or a move to institutional care; and medical compromise. Generally, most depression in people with dementia can be managed in the community.

Depression is common in people with dementia, and the relationship between mood and cognitive symptoms is complex. The nature of this relationship, disease stage, and environmental and clinician factors all contribute to underdiagnosis and undertreatment. Although evidence regarding antidepressant treatment is limited and equivocal, there is no cause for therapeutic nihilism. Organic causes of depressed mood should be excluded, physical health optimised, and medications, where possible, rationalised. Best management includes individually tailored psychosocial strategies and, in moderate to severe depression, judicious use of antidepressant medication with a “start low, go slow” approach. Regular review and effective engagement of carers are both essential and may have significant positive impacts for patients and carers. Difficult-to-treat or complex depression is an indication for specialist referral.