Depression is highly prevalent in RA patients. Estimates varied according to the way in which depression was measured, but our pooled estimates from the small number of studies using gold standard clinical interviews suggest that major depression is present in 16.8% of RA patients. The larger number of studies using screening tools found significant depressive symptoms present in 38.8% using the PHQ-9 and between 14.8% and 48% using the HADS. These prevalence estimates are considerably higher than those observed in the general population [1
] and are similar to, or higher than, those observed in patients with diabetes [24
], Parkinson’s disease [25
] and cancer [26
]. Although studies varied widely in terms of quality (and many were of poor quality), our sensitivity analyses indicate that prevalence estimates were reasonably stable. Apart from the measurement tool used to ascertain depression, study quality and study population had little impact on the estimates detected.
The RA patient population represents a largely female, older adult population [27
]. It could be suggested that the inflated levels of depression found in this sample represent the increased risk of depression found in females and the elderly [28
], regardless of the presence of RA. However, as we found a significant negative association between age and depression prevalence estimate, it is more likely that our findings represent and increased risk of depression in RA patients in comparison with the general population.
A bewildering diversity of assessment measures were used to ascertain depression. This is similar to the situation in other physical diseases [30
]. In this review, we did not include many studies that did not use validated measures of depression or questionnaires that assess a broader overlapping concept of psychological distress. Nevertheless we found that many studies used idiosyncratic cut-off scores on screening tools, meaning that the range of estimates for one such measure (the HADS) varied from 14.8% to 48%. Because there have not been validation studies to determine the best cut-point for such screening tools in this population, one clear recommendation is that investigators justify the use of idiosyncratic thresholds, and always report prevalence at conventional cut-points as well, to allow cross-study comparisons.
We used rigorous methods to conduct the review, with a sensitive search, and a reproducible, structured approach to data extraction and synthesis. We took a broadly inclusive approach to inclusion of studies, preferring to include less rigorous studies and explore the impact of study design in sensitivity analyses than to exclude such studies from the outset. It is possible that publication bias affected our results. We explored this using funnel plots and Egger’s test where the assumption made was that small studies reporting low prevalence of depression would be less likely to be published than small studies reporting high prevalence. We only found evidence of potential publication bias in the studies that used diagnostic interviews. This is surprising since the efforts taken to conduct such studies are considerable and we would have anticipated these to be least likely to be affected by publication bias.
There are, however, additional important shortcomings in the evidence on prevalence of depression in RA that need to be addressed. The limited number of studies using structured clinical interview and determining depression according to DSM and ICD criteria is a concern. The high rates of depressive symptomatology detected through the screening tools could be due to the overlap between the somatic symptoms of depression and symptoms of RA. Symptoms frequently associated with depression (such as fatigue and reduced sleep quality) may be experienced by RA patients regardless of whether depressive symptoms are present or not. For example, 7 out of the 21 BDI items assess somatic symptoms, leading to concerns about the validity of this questionnaire in medical patients [31
]. Similarly, a modified version of the CESD has been suggested for use with patients with RA, due to the symptom overlap [32
]; however, only two articles in the current review used the modified versions available [33
A further consideration is the representativeness of the sample from which prevalence levels are estimates. Low socio-economic status (SES) patients are often under-represented in research samples [35
]. This can be problematic, as low SES is associated with increased susceptibility to depression [36
] and RA [37
]. Many of the studies included in this review did not measure SES appropriately, with most studies using a single measure of education level or monthly income to indicate SES. This level of heterogeneity makes it difficult to establish the representativeness of the samples included with regard to SES. However, it is possible that a selection bias favouring high SES patients exists and the results of this systematic review may therefore underestimate the prevalence of depression.
The meaning of depression in the context of RA is not straightforward. Emotional responses to a physical illness characterized by pain and debility are understandable, and somatic symptoms of depression (e.g. loss of appetite and poor sleep) might be expected as part of RA. Therefore there is a need to ensure that measures of depression used in clinical practice are validated, both against a recognized criterion (e.g. the ‘gold standard’ clinical interviews) and also in terms of predictive validity (i.e. to determine the impact of depression on RA outcomes). Psychometric approaches utilizing longitudinal data may further be able to distinguish subtypes of depressive symptoms and thereby distinguish symptoms that are most likely to be core to the depressive syndrome.
Ultimately the key question is whether improved patient outcomes can be attained by recognizing and managing depression more effectively. There is growing evidence that incorporating a system of collaborative and stepped care of depression in patients with physical illness, which might include routine screening for depression with referral for highly structured manualized therapies depending on the outcome of screening, is effective treatment [38
]. The high prevalence of depression in RA suggests that this would be a suitable patient group in which to test such strategies.
Rheumatology key messages
- Depression is highly prevalent in RA patient groups.
- Increased depression prevalence in RA is significantly associated with low mean age.