East Asian Arch Psychiatry 2012;22:12-7

ORIGINAL ARTICLE

Cognitive Function, Functional Performance and Severity of Depression in Chinese Older Persons with Late-onset Depression

华裔老年晚发性抑鬱症患者的认知功能、功能特性和抑鬱症严 重程度研究

谭焕芝、林翠华

Dr Cindy Woon-Chi Tam, FHKCPsych, FHKAM (Psychiatry), Department of Psychiatry, North District Hospital, Hong Kong SAR, China.
Prof Linda Chiu-Wa Lam, FHKCPsych, FHKAM (Psychiatry), Department of Psychiatry, The Chinese University of Hong Kong, Hong Kong SAR, China.

Address for correspondence: Dr Cindy Woon-Chi Tam, Department of Psychiatry, Psychiatric Outpatient Department, North District Hospital, 9 Po Kin Road, Sheung Shui, New Territories, Hong Kong SAR, China.
Tel: (852) 2683 7620; Fax: (852) 2683 7616; Email: tamwoonchi@hotmail.com

Submitted: 19 September 2011; Accepted: 11 November 2011

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Introduction

Depression in late life is associated with significant morbidity, including deficits in a range of cognitive functions and considerable functional impairment and disability. The relationship between cognitive status and depressive symptoms and their effects on functional decline are of significant clinical and public health importance, because both are common, frequently coexist, and may be treatable.

Neurocognitive deficit involving executive dysfunction is common when first onset of depression occurs in late life. A number of clinical factors might be linked to neuropsychological decline in late-onset depression.^1-3 Even after controlling for the effects of demographic variables, there is still an effect of depressive severity on cognitive function.

The relationship between disability and depression is even more complex and probably bidirectional. In a systematic review of variables predicting functional decline in community-dwelling older adults, depression was one of the key risk factors identified.⁴ Beekman et al⁵ reported that both major and minor depression were associated with disability. Lyness et al⁶ reported that functional outcomes associated with subsyndromal or minor depression were not as poor as for those among patients with major depression, but poorer than observed for those who were non-depressed.

Previous studies of clinically non-demented community-dwelling Chinese elderly in Hong Kong found that executive dysfunction, depressive symptoms, apathy, and mild parkinsonian signs (MPS) were associated with functional disability.^7-9 However, information about the functional correlates in Chinese elderly with late-onset depression was limited. Chan et al^10,11 found that depressed Chinese elderly had poorer self-perceived quality of life and that quality of life correlated with the level of depression and functional limitations. It would be important to investigate how the severity of mood symptoms and physical health affects cognitive and functional performance in this group with significant mood disturbances.

In the current cross-sectional study, we aimed to investigate the relationship between cognitive performance and severity of depression in Chinese elderly subjects with late-onset depression. The second aim was to examine the impact of cognitive function and mood symptoms on functional performance in depressed Chinese elderly. Investigating the relationship between these factors might provide insight into the underlying pathology of late-onset depression and help identify those at high risk and greater disability for further investigation.

Methods

Sample

Patients aged ≥ 60 years who fulfilled DSM-IV criteria¹² for major or minor depression were recruited from psychiatric outpatient clinics and the inpatient psychiatric unit in the New Territories East Cluster hospitals in Hong Kong from year 2007 to 2009. The onset of the first depressive episode had to be at the age of 50 years or older.

Each depressed subject was evaluated by a qualified psychiatrist to establish eligibility for inclusion in the study, a clinical diagnosis, and a clinical staging assessment using the Clinical Dementia Rating (CDR) scale.¹³ Subjects with a global CDR score of 0 or 0.5 were recruited.

Subjects with a history of degenerative neurological disorder, dementia, cortical strokes, severe or unstable physical illness (i.e. those who had been hospitalised in the last 3 months), and a history or current substance / alcohol abuse were excluded. Subjects who had had electroconvulsive therapy in the past 3 months were also excluded. The psychiatrists explained the procedure and obtained written consent from the participants or their caregivers. This study was approved by the Joint CUHK-NTEC Clinical Research Ethics Committee. An experienced research assistant performed the cognitive and functional assessment.

Assessments

All depressed patients underwent a comprehensive psychiatric, cognitive and functional assessment. Depression was diagnosed according to DSM-IV criteria and symptom severity was rated using the 24-item Hamilton Depression Rating Scale (HDRS).¹⁴

Cognitive Tests

Global cognitive assessment was estimated using the Cantonese version of the Mini-Mental State Examination (CMMSE)¹⁵ and the Chinese version of the Alzheimer’s Disease Assessment Scale–Cognitive subscale (ADAS- Cog).¹⁶ To test for episodic memory, subjects were also examined using a 10-minute delayed recall of a word list from the ADAS-Cog. Digit span and visual span tests were carried out to test attention and working memory. The Category Verbal Fluency Test (CVFT)¹⁷ and Trail Making Test (TMT) were performed as executive function tests.¹⁸ In the CVFT, subjects were asked to generate exemplars in the categories of animals, fruit, and vegetables within 1 minute. Combined scores were then computed. Trail Making Test– Part A (TMT-A) was used to assess processing speed. Trail Making Test–Part B (TMT-B) additionally measured mental set shifting and response inhibition. We modified TMT by changing the sequence of alphabets to Chinese writing of

numbers with ascending order, as most subjects had not received an English language education.

Disability Assessment for Dementia Scale

The Disability Assessment for Dementia scale (DAD) is a validated measure of activities of daily living (ADL) designed specifically for use in patients with dementia. The Chinese version of DAD has been validated in Chinese subjects.¹⁹ It evaluates instrumental ADL (meal preparation, telephoning, going on an outing, finance, medication, leisure, and housework) and basic ADL (hygiene, dressing, undressing, continence, and eating) through the caregiver observations of the subject’s actual performance in the previous 2 weeks.

Neuropsychiatric Symptoms

Neuropsychiatric symptoms were identified using the Chinese version of Neuropsychiatric Inventory (NPI)

Motor Signs

Motor symptoms including axial dysfunction, bradykinesia, rigidity and tremor were assessed by the Unified Parkinson’s Disease Rating Scale–motor subscale.²² The MPS score was calculated by summing up the scores in this scale.

Medical illness burden was assessed by the Cumulative Illness Rating Scale (CIRS).²³ The CIRS is a measure of physical illness in which a cumulative score is derived from ratings of severity of impairment in each of 13 organ systems. In addition, presence of cardiovascular risk factors and vascular diseases including hypertension, diabetes mellitus, hyperlipidaemia, heart disease, arrhythmia, and cerebrovascular accidents were recorded. A combined cardiovascular risk score was calculated by summing up the total number of these risk factors.

Statistical Analyses

Statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS 17.0; SPSS Inc., Chicago [IL], US). Spearman correlation analyses were performed to assess the association between functional disability and mood scores. Factors that correlated with the DAD scores at p < 0.05 were entered as explanatory variables. Multiple linear regression analyses were performed to examine the predictors for DAD scores.

Results

A total of 105 subjects were recruited. The demographic characteristics of the subjects are summarised in Table 1. The mean depressive score reflected that they suffered from mild-to-moderate depression.

Factors Affecting Cognitive Performance in Depressed Subjects

Relationship between Clinical Characteristics and Cognitive Test Scores

Neither medical nor cardiovascular risk burden correlated significantly with cognitive test scores. Nor did age of onset of depression or duration of the current episode correlate with cognitive test scores.

Relationship between Mood Symptoms and Cognitive Test Scores

The HDRS and NPI-depression scores correlated with cognitive scores involving multiple domains, while NPI- apathy scores mainly correlated with executive test scores (Table 2).

Table 3 shows the correlations between cognitive test scores and mood symptom severity after controlling for age and education, in which case the severity of depression nevertheless correlated significantly with CMMSE scores, the forward visual span test scores, TMT-A scores, and negatively with CMMSE score after controlling for age and education. The extent of correlation between mood symptoms and cognitive test scores decreased after adjusting for age and education, except that between the severity of depression and TMT-A scores.

Factors Affecting Functional Performance in Depressed Subjects

Table 4 shows the relationship between clinical and cognitive correlates and functional scores. The predictors for DAD scores are shown in Table 5. Apathy, performance in the executive test (TMT-B), depression severity, and MPS were independent predictors of functional performance among depressed subjects.

Discussion

According to our results, the severity of depression correlated with impairment in working memory, episodic memory, and slowing of processing speed among the elderly with late-onset depression. Apathy did not correlate with performance in the executive function test after controlling for age and education. Baudic et al²⁴ also found that deficits in executive function and memory correlated with the depression severity in the elderly. They suggested that memory failure in these patients might reflect impairment in retrieval processes, which in turn depends on executive function. Sheline et al³ suggested that changes in processing speed fully mediated the influence of depression severity on all other cognitive domains (executive function, language and working memory). It was also proposed that frontostriatal limbic abnormalities predispose to both depressive symptoms and executive dysfunction in older adults.²⁵

Sheline et al³ found significant associations between vascular burden and cognitive performance, which could not be replicated in our study. The fact that our subjects had a relatively low cumulative medical and cardiovascular risk burdens might explain this observation.

According to our results, the severity of depression, and the presence of apathy, MPS, and executive dysfunction were independent predictors of functional performance in depressed subjects. The findings were similar to those reported for community-dwelling Chinese elderly with questionable dementia.^7-9 Age, education level, medical burdens, and cardiovascular risk burden were not significant predictors of functional ability. The findings also echoed the observations by Alexopoulos et al²⁶ that patients with depression-executive dysfunction (DED) syndrome had reduced fluency, impaired visual naming, loss of interest in activities, psychomotor retardation, poor understanding of their disease, and pronounced disability. Major contributors to disability in patients with DED syndrome were psychomotor retardation, depressive symptomatology, and loss of interest in activities. Executive dysfunction is strongly related to instrumental ADL (IADL) impairment in depressed elderly patients.²⁷ Kiosses and Alexopoulos²⁸ found that impairment in initiation / perseveration had the most prominent effect in the presence of depressive symptoms and affected IADL in such elderly. Sanders et al²⁹ found associations between components of executive dysfunction (Trial B, Mattis-IP scores) and functional disability that were independent of depression. Since both geriatric depression and executive dysfunction often occur in patients with frontostriatal impairment, these observations raise the question of whether disability is an early indicator of impairment of the frontal and prefrontal areas.

Based on our findings, 2 mechanisms were proposed to explain the functional disability among depressed subjects. First, depressed elderly were apathetic and lacked interest in participating in joyful activities. They were unlikely to initiate or persist with complex and cognitively demanding tasks or hobbies. Secondly, they had executive dysfunctions and difficulties in planning, organisation, active problem- solving, anticipation of possible consequences, monitoring the accuracy and the effectiveness of their own behaviour. Executive processes are fundamental to the daily functioning of depressed older adults, and dysfunction may lead to a lack of compensatory strategies that improve outcomes in late-life depression and increase dependency. Clinicians should be aware that both executive deficits and depression correlate with poorer overall functioning and should consider incorporating more thorough cognitive and functional assessments into their evaluations of older patients who are depressed. Specific interventions targeting executive dysfunction and functional impairment might benefit specific subgroups of late-onset depression.

The strengths of this study were the inclusion of a heterogeneous sample of elderly with late-onset depression to maximise the generalisability of findings, and the use of established and validated measures of depression, cognitive function, and functional ability. However, we recruited a clinical sample with mild-to-moderate depressive syndromes. The generalisability of the results to community- dwelling elderly with subsyndromal depression in primary care needs to be confirmed in other studies. Our cross- sectional analyses only allowed us to examine associations between factors but we could not confirm the underlying causal relationship. Moreover, the correlations between mood symptoms, cognitive test scores and functional scores were only modest.

Our study highlighted the importance of multidimensional evaluation of geriatric depressed patients. Treatment should also aim at remission of depressive symptoms, and amelioration of cognitive impairment and functional disability. Future research about the trajectory of depression remission and functional decline could enrich knowledge about the bidirectional relationship between depression and functional disability.

In conclusion, late-onset depression affects mood, cognition and functional ability in the elderly. Our observations supported the functional importance of executive dysfunction and depression in the depressed elderly. Lack of interest and motivation, depressive mood, compounded by behavioural abnormalities (resulting from executive dysfunction), may account for functional disability in elderly subjects with late-onset depression.

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