Screening for major depressive disorder

All subjects were screened for past and present major depressive symptoms. It has been documented that depression amongst the elderly is grossly underestimated (Snowdon and Lane, 2001) and may be concealed by an increase in somatic symptoms, such as fatigue and sleep problems.

Whilst depression is common in the early stages of Alzheimer’s disease (van Oijen et al., 2007) it may also be a prodrome to dementia of the Alzheimer’s type (Wilson et al., 2008). Thus, clinical judgement is required in combination with the use of scales when screening for major depression and identifying other underlying causes.

During the course of the study, two self-report scales were used to screen for depression. Initially, when the focus of the study was based on clinical referrals, the Depression Scale from the Psychogeriatric Assessment Scales (Jorm and Mackinnon, 1995; Jorm et al., 1995) was used. However, when the study was modified in 2001 (and subjects under the age of 65

years were included), the GDS-15 (Sheikh and Yesavage, 1986) was subsequently used to screen for depression.

To align the scoring systems of both screening scales, the cut-off scores from both scales; Depression Scale (PAS) and GDS were used to categorize subjects as 0, (no depression), to indicate the absence of clinically significant depressive symptoms (i.e., the subject scored within the normal range); 1, to indicate mild depressive symptoms (i.e., the subject scored between 5-7 on the PAS or 8-9 on the GDS), and 2 to indicate clinical signs of depression (i.e., the subject scored >10). This allowed for both groups to be rated for depression on the same scoring system, despite the use of two different scales. The cut-off scores on the GDS-15 are similar to those employed by Freidman et al. (2005). Friedman et al. (2005) looked at depression in subjects over the age of 65 (mean age=80) and used a similar cut-offs to the present study to determine the severity of depression. That is, Friedman et al. used a score from 6-10 to classify subjects as having mild depression and a score from 11-15 to classify subjects as having severe depression.

Subjects were excluded if they scored within the depression range on either assessment. In the present study, subject number 75 was rated as having clinical signs of depression. This subject spoke about stress and anxiety in her life and felt overburdened caring for her grandchildren. This subject was advised to see her GP for treatment and was excluded from the analysis. Eight subjects who were rated as having mild depressive

symptoms were not excluded from the analysis, but were used to assess the influence of increased depressive symptomatology on memory complaints.

6.5.3.1 The Psychogeriatric Assessment Scale (PAS) (Jorm and MacKinnon, 1995)

The Stroke Scale

The Stroke Scale is part of the Psychogeriatric Assessment Scale (Jorm and MacKinnon, 1995). This scale evaluates six symptoms of cerebrovascular disease. It provides an indication of whether cognitive impairment might be due to vascular dementia or non-vascular types of dementia (mainly Alzheimer’s disease) (see page A3). Subjects with vascular dementia obtain higher than average scores on this scale. The validity of the Stroke Scale is demonstrated by its correlation with the Hachinski Ischemic Score; 0.71 and 0.65 (Jorm et al., 1995). Approximately, 80% of vascular dementia cases obtain a score of one or more (Jorm and MacKinnon, 1995).

The scores range from 0 to 6 with scores of 2 or more indicating the possibility of vascular dementia. None of the subjects in the present study reported a history of stroke or transient ischaemic attacks (T.I.A).

The Depression Scale

The Depression scale evaluates 12 symptoms of depression over the previous two weeks (see page A4). For example, “Have you had trouble sleeping over the past two weeks?” The scale focuses on the physical and cognitive symptoms of depression. The reference population used for determining the psychometric properties of the scale consisted of 134

geriatric and psychogeriatric patients from Sydney and Geneva, over the age of 70 years. Reports indicate that the Depression Scale performs well as a screening test for major depression (Jorm et al., 1995). Test-retest reliability for the Depression Scale is high and the validity of the scale is supported by its correlation with the Goldberg depression and anxiety scales, 0.67 and 0.60 respectively. Approximately 80% of major depression cases obtain a score of four or more (Jorm and MacKinnon, 1995).

6.5.3.2 The Geriatric Depression Scale (Sheikh and Yesavage, 1986) The Geriatric Depression Scale (GDS) is a reliable and valid screening tool to detect the presence of a major depressive disorder amongst older persons in different settings (Sheikh and Yesavage, 1986). It is used extensively in geriatric populations (Almeida and Almeida, 1999; D’Ath et al., 1994; Friedman et al., 2005; Jongenelis et al., 2007) and is favoured because it excludes somatic symptoms of depression known to occur in the elderly that frequently are related to causes other than depression. In the present study, subjects were administered the GDS-15 Short Form which has been validated for a diagnosis of major depressive episode according to the ICD-10 and DSM-IV criteria, for research and clinical purposes (Almeida and Almeida, 1999). The GDS-15 consists of 15 questions enquiring about different aspects of depression in relation to mood and activity, e.g., ‘Do you think it is wonderful to be alive now?’ Subjects either responded with a ‘yes’

or ‘no’ answer to each question (see page A7). The responses to the 15 questions were summed to give a total score from 0 to 15, with higher

scores indicating more depressive symptoms. A cut-off score of 5 or more indicates probable depression, but not necessarily major depression (D’Ath et al., 1994).

Reliability data supports the clinical utility of the GDS-15 for measuring depression. D’Ath et al. (1994) screened elderly subjects over 75 years for depression using a cut-off score of 4/5, and reported high sensitivity (91%) and specificity (72%). The internal consistency for the GDS-15 is also high (Cronbach’s alpha = 0.80) and all of the 15 items are significantly associated with the total score and hence ‘caseness’ (D’Ath et al., 1994). However, internal consistency declines with increasing severity of dementia. The GDS-15 has high test-retest reliability (0.84 to 0.85) for short intervals (less than 2 weeks). This test correlates well with other measures of depression, (e.g., Beck Depression Inventory (r=0.84) and the Zung Self-Rating Depression Scale (r=0.68) which are used for assessing depression in younger age groups.