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Point prevalence and correlates of depression in a national community sample with multiple sclerosis
General Hospital Psychiatry
The prevalence of depression in multiple sclerosis (MS) is known to be elevated, but nearly all available studies have estimated period prevalence. The objective of this study was to estimate the point prevalence of depression in a representative community sample using the Patient Health Questionnaire, Brief (PHQ-9).
The data source for this study was the Survey of Living with Neurological Conditions in Canada, which was derived from a representative sample of household residents.
The sample included 630 respondents with MS. With application of the standard PHQ-9 cut point (10 +), the prevalence of depression was 26.0% (95% confidence interval 18.9%–33.0%). Depressed subjects had lower quality of life; an increased frequency of suicidal ideation; and more often reported a negative disease course, high stress, low social support and stigmatization.
This study adds to the existing literature by providing point prevalence data: in any 2-week period, about one quarter of community residents with MS experience substantial levels of depressive symptoms.
Keywords: Cross-sectional studies, Depression, Multiple sclerosis, Prevalence, Population studies, Comorbidity.
Numerous studies have evaluated the prevalence of depression in clinical samples with multiple sclerosis (MS). Such studies are potentially flawed by selection bias. Illness severity or even depression itself may influence health care use in ways that could distort such estimates. Only two studies have examined the prevalence of depression in a representative community sample. One, using a short form version of the Composite International Diagnostic Interview  , reported a 15% annual prevalence of major depressive episode, approximately three times that of the general population  . Another study employed the Hospital Anxiety and Depression Scale (HADS) in a community sample in Southern Tasmania  . Using a cut point of 8 +, a prevalence of 18.5% was reported, approximately twice the reported prevalence in an otherwise comparable non-MS population  .
For health services considerations, the most important type of prevalence is point prevalence: the proportion of a population with depression at a point in time. Apart from the HADS-based estimate noted above, there are no population-based point prevalence estimates for depression in MS.
The opportunity to conduct this analysis arose as a result of a study called the Survey of Living with Neurological Conditions in Canada (SLNCC). This was a cross-sectional survey linked to a large, annual general health survey, the Canadian Community Health Survey (CCHS). The CCHS uses a probability sample of approximately 70,000 subjects and inquiries about professionally diagnosed long-term medical conditions. For 2 years (2010 and 2011), the CCHS included such questions for 18 neurological conditions, and participants with affirmative responses were recruited to participate in the SLNCC. Survey respondents were also asked whether there were household members that had one or more of these neurological conditions, and those identified were also asked to participate in the SLNCC. SLNCC data were subsequently collected using computer-assisted telephone interviews between September 2011 and March 2012.
The SLNCC sampled the population 15 years and over who were household residents in one of Canada’s 10 provinces. The final sample consisted of 8200 people with neurological conditions. The estimated response rate was 81.6%  . Standard items were used to assess age, sex, level of education and household income. There were also general health items, perceived stress items and brief (four-item) scales assessing social support and stigma. The stigma items referred specifically to MS (e.g., “Because of my multiple sclerosis, some people avoided me.” The Health Utility Index, Mark III (HUI3)  was also included. This is a quality-of-life scale providing utility-weighted ratings for individuals’ overall health status, as assessed through eight dimensions. HUI3 scores less than < 0.70 are generally regarded as providing evidence of severe disability  . To assess depression, the Patient Health Questionnaire, Brief (PHQ-9) was included  . This scale has nine items, each scored 0–3, for a total possible score of 27, with an optimal cut point of ≥ 10. Unlike other depression rating scales, the PHQ-9 items align with those of theDiagnostic and Statistical Manual of Mental Disorders, Fourth Edition,‘A’ criteria for major depression. The full questionnaire, including all of the measures mentioned above, is available on the Statistics Canada Website  .
In order to account for survey design effects such as clustering and unequal selection probabilities, the use of replicate sampling weights and bootstrapped variance estimation are recommended by Statistics Canada  . The replicate weights (n= 500) also include adjustments for nonresponse and “out of scope” (e.g., subjects excluded because the reported diagnosis could not be confirmed) status. The set of replicate bootstrap sampling weights used in this analysis was that developed for the SLNCC by Statistics Canada. The odds ratio (OR) was used to examine depression correlates.
There were 630 SLNCC respondents with MS. They were 73.3% female, and the mean age was 51.8 years. Additional descriptive information is provided in Table 1 . The respondents reported a mean age of MS onset of 37.0 years. The mean number of years since diagnosis with MS was 14.8, and the mean number of years since symptom onset was 18.8.
|High school graduate or less||37.1%||31.1–43.2|
|Greater than high school graduation||62.9%||56.8–68.9|
|Annual household income|
|Less than $30,000||24.7%||18.7–30.6|
|Greater than $30,000||75.3%||69.4–81.3|
|Self-perceived general health|
|Suicidal ideation a||8.9%||5.2–12.6|
|HUI (< 0.7)||58.7%||51.1–66.2|
a Based on item 9 of the PHQ-9; indicates suicidal ideation on several days in the preceding 2 weeks.
The overall prevalence of depression according to the PHQ-9 cut point (≥ 10) was 26.0% [95% confidence interval (CI) 18.9–33.0]. The PHQ-9 can also be scored using an algorithm that reflects diagnostic criteria  . It requires endorsement of the two obligatory symptoms, a total of five symptoms endorsed at least “most of the time” or suicidal ideation at the “several days” level. According to the algorithm, the prevalence was 11.9% (95% CI: 5.9–18.0). The remainder of the report uses cut point derived frequencies.
Table 2 presents associations with other variables. No significant age or sex differences were observed. Associations were seen for several depression risk factors or impacts: low social support, high stress, perceived stigmatization and low household income. A majority of respondents fell into the low-HUI3 category (see Table 1 ). Depression was nevertheless strongly associated with low quality of life ( Table 2 ).
|OR||95% CI||P value|
|Age category||35–65 years a||1.2||0.5–3.3||.66|
|Education||Less than high school||0.5||0.2–1.1||.09|
|Annual household income||<$30,000||2.5||1.1–5.7||.03|
|Perceived general health||Worse compared to 1 year ago||3.3||1.6–7.2||.002|
|HRQoL b||HUI < 0.7||9.4||2.9–30.4||< .001|
|HRQoL b||HUI < 0||10.2||2.7–38.5||.001|
|Social support||Lower quartile||4.8||2.2–10.4||< .001|
|Stress (most days)||High||4.2||1.8–9.8||.001|
|Stigma||Upper quartile score||6.5||3.0–14.1||< .001|
a The baseline category consisted of those < 35 or > 65.
b Health-related quality of life; quantified by the HUI as a preference-weighted health utility. A score of less than zero indicates a health state associated with a preference lower than death.
These results confirm the markedly elevated prevalence of depression in MS and more negative health status associated with depression. Previous Canadian population-based estimates using the PHQ-9 reported much lower prevalence in the general population: 8.4% for the cut point and 3.3% for the algorithm scoring  . Irrespective of the scoring strategy used, the prevalence remains approximately three times higher than that of the general population, consistent with previous annual prevalence data  , whereas the point prevalence estimate of Wood et al. using the HADS was approximately twice that of the general population. The prevalence of suicidal ideation was high in this sample at 8.9%. A previous Canadian population survey using the PHQ-9  found a 2.8% (95% CI 2.3–3.4) frequency of endorsement.
Causal inferences cannot be made from this cross-sectional data. Striking associations between depression and perceived health, quality of life, income, social support, stress and stigma were observed. Such variables may cause or be caused by depression. The response rate in the SLNCC was good (> 80%), but nonresponse may nevertheless have affected the prevalence estimate. Concerns have been expressed that an overlap of symptoms between depression and MS could lead to false-positive ratings. However, the PHQ-9 appears to perform well in people with MS  , supporting the validity of these estimates.
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a Department of Community Health Sciences, University of Calgary, Canada
b Department of Psychiatry, University of Calgary, CANADA
c Department of Clinical Neurosciences and the Hotchkiss Brain Institute, University of Calgary, Canada
d Mathison Center for Mental Health Research & Education, Hotchkiss Brain Institute, University of Calgary, Canada
☆ Disclaimer: This research and analysis were based on data from Statistics Canada but the opinions expressed do not represent the views of Statistics Canada.
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