East Asian Arch Psychiatry 2015;25:146-149

ORIGINAL ARTICLE 

Dr Mimi M. C. Wong, MBBS, MRCPsych, FHKAM (Psychiatry), FHKCPsych, Department of Psychiatry, United Christian Hospital, Kwun Tong, Hong Kong SAR, China.
Dr C. F. Chan, MBChB, MRCPsych, FHKAM (Psychiatry), FHKCPsych, Castle Peak Hospital, 1/F, Block F, Tuen Mun, Hong Kong SAR, China.
Dr S. W. Li, MBBS, MRCPsych, FHKAM (Psychiatry), FHKCPsych, Castle Peak Hospital, 1/F, Block F, Tuen Mun, Hong Kong SAR, China.
Ms Y. M. Lau (Diploma in RMN, MBA [HCA]), Castle Peak Hospital, 1/F, Block F, Tuen Mun, Hong Kong SAR, China.

Address for correspondence:
Tel: (852) 2379 9611; Fax: (852) 2717 1394; Email: wmc009@ha.org.hk

Submitted: 8 May 2015; Accepted: 9 July 2015 

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Introduction

The prevalence of late-onset depression is estimated to be 15% among people aged ≥ 65 years, making it an important mental illness in the elderly population.¹ It often arises in the context of medical and neurological disorders.² It is frequently associated with cognitive impairments, suggesting a close relationship between the two.^3,4 Cognitive impairment has been considered an accompanying symptom of depression and presents a clinical picture that resembles dementia (pseudodementia).⁵ Nonetheless it is now more commonly believed that depression may be an early manifestation of dementia.⁶ Early depressive symptoms among cognitively impaired individuals may represent an important preclinical sign, and confers an increased risk for impending Alzheimer’s disease or vascular dementia among old people.^7-9 Their high co-morbidity may also be attributed to risk factors common for both disorders, mainly vascular risk factors.¹⁰

There is increasing evidence that the cognitive impairment in elderly depressed patients is irreversible since recovery from depression is generally not accompanied by improvement in cognitive performance.^11,12 Lack of improvement in cognition following treatment for depression may be associated with an increased risk of later dementia.¹³ Self-reported decline in functional activities may be a marker for persistent cognitive impairment.¹² Nonetheless cognitive impairment has no negative impact on recovery from depression.^11,14

One of the objectives of this study was to assess cognitive performance in elderly depressed patients after they had received 6 months’ treatment for depression. We hypothesised that cognitive impairment at baseline would persist at follow-up despite improvement in depression. We also hypothesised that individuals with persistent cognitive impairment at 6 months had greater functional impairment at baseline. We also aimed to determine the remission rate of depression after 6 months of treatment.

Methods

The study was performed in a consecutive group of patients aged ≥ 65 years with depression who presented to the fast track clinic (FTC) of the Elderly Suicide Prevention Programme (ESPP) of Castle Peak Hospital, Hong Kong. The ESPP was founded in Hong Kong in 2002 with an aim of early detection of elderly at risk of suicide and to provide effective and adequate management to this group of patients. Castle Peak Hospital is 1 of 7 centres with an ESPP that caters to all referrals of elderly with suspected depression with or without suicidal attempt and who live in the New Territories West Cluster of Hong Kong where the population is about 1.1 million.

Inclusion criteria of the study were a diagnosis of depressive disorder (according to the ICD-10 criteria) and an onset of depression at age ≥ 50 years. Patients were excluded if they had other psychiatric diagnoses such as organic disorder, e.g. dementia, psychotic disorder, or a history of alcoholism or neurological disease.

Demographic data collected included age, gender, marital status, living status, education level, physical health status, and the presence of vascular risk factors. Vascular risk factors, including hypertension, diabetes mellitus, hyperlipidaemia, heart disease and cerebrovascular accident / transient ischaemic attack, were recorded. The number of risk factors was added to give a combined total score for vascular risk burden.

Assessment

The diagnoses of patients were made after clinical assessment by the case doctor and multidisciplinary case discussion chaired by an Associate Consultant of ESPP. Severity of depression was assessed using the Hamilton Depression Scale (HMD),^₁₅ cognitive performance by the Hong Kong Montreal Cognitive Assessment (HK-MoCA),¹⁶ and functional level by the Instrumental Activities of Daily Living Scale (IADL).¹⁷ The HK-MoCA is a useful cognitive screening instrument for use in older Chinese adults. The cutoff score for diagnosis of mild cognitive impairment was 21/22 with a sensitivity of 0.828, specificity of 0.735, and area under the curve of 0.920.^18,19 It was found to have high test-retest, inter-rater reliability, and internal consistency.¹⁹ Its clinical utility in Chinese elderly subjects with predominately low education is generally good.¹⁶ The HK-MoCA and HMD were performed at baseline and repeated 6 months after presentation to the FTC. Patients were treated according to the management plan of their respective case doctors.

Data Analysis

Data were analysed using the Statistical Package for the Social Sciences Windows version 16.0 (SPSS Inc., Chicago [IL], US). For continuous data, variables were presented as mean and standard deviation for normally distributed data or as median and interquartile range (IQR) for skewed data. The Kolmogorov-Smirnov test was used to test for normality. For categorical data, variables were presented as numbers and percentages. The Mann-Whitney U test was used to compare continuous variables with skewed distribution if there were only 2 groups. For comparison of categorical data, the Pearson’s Chi-square or Fisher’s exact test was used. Spearman’s rank correlation coefficient was used to test for correlation of continuous variables with skewed distribution. The course of affective symptoms and cognitive performance was studied by means of paired Student’s t tests. Patient groups, such as cognitively impaired versus cognitively unimpaired, were compared using unpaired t tests or Chi-square tests.

Results

A total of 57 patients fulfilled the inclusion criteria but 5 were excluded as they were also diagnosed to have dementia; 52 patients were recruited. The demographic characteristics are summarised in the Table. In all, 47 (90.4%) were treated with antidepressants that included serotonin selective reuptake inhibitor, serotonin-noradrenaline reuptake inhibitor, noradrenergic and specific serotonergic antidepressant, and serotonin antagonist and reuptake inhibitor. Benzodiazepine was prescribed in 15 (28.8%) patients and hypnotics in 14 (26.9%). The number of vascular risk factors ranged from 0 to 4 (median, 1.29; IQR, 1.2). The difference in HMD and HK-MoCA scores at baseline and at 6 months was significant (p < 0.001, t test).

Course of Cognitive Impairment

In all, 28 (53.8%) patients were found to have cognitive impairment (HK-MoCA score < 22) at baseline. No significant difference was found in the demographic and clinical characteristics for those with or without cognitive impairment. Eight (28.6%) demonstrated improvement in their HK-MoCA score which returned to normal level after 6 months. In 3 (5.8%) patients HK-MoCA score deteriorated from within the normal range at baseline to below normal cutoff at 6 months. The change in cognitive impairment grouping was significant (p < 0.001, Chi-square test). In all, 23 (44.2%) patients had cognitive impairment at 6 months. This cognitively impaired group was older (mean age, 75 ± 12 vs. 70 ± 6 years) and had a lower IADL score (mean, 18 ± 11 vs. 25 ± 4) than the normal group (p < 0.05). They did not differ in HMD score (both baseline and at 6 months), education level, or number of vascular risk factors.

Course of Depression

At 6-month follow-up, the severity of depression as assessed by the HMD was considerably reduced (from 12.3 ± 6.1 to 5.6 ± 4.1, p < 0.001). Applying a HMD score of ≤ 7 as criterion for remission of depression,²⁰ 32 (61.5%) patients were considered to be in remission and 20 (38.5%) were not. There was no difference in their age, education level, number of vascular risk factors, IADL score, or cognitive impairment at admission and that at 6 months. Nonetheless mean baseline HMD score (15.55 ± 6.5) and HMD score at 6 months (10.1 ± 2.4) were significantly higher in those not in remission (vs. 10.28 ± 5.0 at baseline and 2.81 ± 1.9 at 6 months in remitted patients). The remission rate was 50% in patients without cognitive impairment and 71.4% in those with cognitive impairment. The difference was not statistically significant.

Discussion

Cognitive impairment constituted a stable feature in a considerable number of elderly patients with depression. Those with greater baseline functional impairment had more persistent cognitive impairment at 6 months. It is possible that cognitive impairment requires a longer time to improve than depressive symptoms. About two-thirds of patients achieved remission of depression after 6 months of treatment.

Our study and the findings of Adler et al¹¹ revealed that in most cases treatment of depressed patients who are cognitively impaired results in improvement in depression after 6 months of treatment, but not cognitive impairment. This is in accordance with other studies that have reported no or only minor improvements in cognitive performance following treatment of late-life depression and recovery from affective symptoms.^7,8 Cognitive impairment is common in depressed older adults, especially in those with late onset of depression⁸ but it has no negative impact on recovery from depression.¹⁴ Nearly half of the patients in our study had cognitive impairment at 6 months. Elderly depressed patients with mild cognitive impairment may be considered to be at increased risk of dementia.²¹ Those who were older and who had a lower functional level at baseline had greater cognitive impairment after 6 months. This supports our hypothesis that functional activity at baseline is a marker for persistent cognitive impairment.¹² Executive processes are fundamental to the daily functioning of depressed older adults. Dysfunction might lead to a lack of compensatory strategies that could improve outcomes in late-life depression and thus lead to increased dependency. Executive dysfunction has been strongly linked to IADL impairment in depressed elderly patients.²² Associations between components of executive dysfunction and functional disability have been identified and are independent of depression.²³

In this study, the mean HMD score reduced significantly after 6 months of treatment and the rate of remission for depression was 61.5%, similar to that of Adler et al¹¹ and slightly less than that of Tam and Lam.²⁴ This may be due to a difference in definition of remission using the HMD score. The study by Tam and Lam²⁴ used a cutoff score of 10 which was higher than that in our study. The non-remitters had a higher baseline HMD score than the remitters. This concurs with the findings of others where greater severity of depressive episode at baseline predicted poor recovery.^24,25 Tam and Lam²⁴ also found that the influence of cognitive deficits on clinical remission became insignificant after controlling for the effects of mood symptoms.

Limitations of this study include the small sample size and the exclusion of patients with late-onset depression who were admitted to a mental hospital. This group of patients would not be followed up by ESPP that targets only community-dwelling elderly with depressive symptoms and a high risk of suicide. Patients who required admission to mental hospital likely had more severe symptoms and a history of suicidal attempt. They thus represented a different group of patients with late-onset depression. Another limitation is the lack of separate analysis for specific components of cognitive functioning.

The results of this study demonstrate the importance of cognitive impairment as a stable feature in a considerable number of elderly individuals with depression. This might suggest an increased risk for the development of dementia. Close monitoring of cognitive functioning is indicated in this group of patients so that early intervention can be offered.

Acknowledgement

We would like to acknowledge the community psychiatric nurses of the Elderly Suicide Prevention Programme of  Castle Peak Hospital who have assisted in data collection process of the study. No financial support was received and there were no conflicts of interest.

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