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Psychological and pharmacological interventions for depression in patients with diabetes mellitus: an abridged Cochrane review: some critical comments

An important meta-analytic review by Baumeister, Hutter and Bengel examined the effects of both psychological and pharmacological interventions for depression in patients with diabetes mellitus [1]. Several of 19 randomized controlled trials, testing psychological (n = 1122) and pharmacological interventions (n = 377) were included: primary outcomes were depression severity, depression remission and glycaemic control. The authors concluded that both interventions had moderate, beneficial effects on depression outcomes in patients with diabetes and depression. The effects of psychological interventions on HbA1c varied considerably, and it was concluded that only selective serotonin reuptake inhibitors improved HbA1c. In this letter, we aim to describe some concerns regarding this meta-analytic review. First, we believe that the forest plot summarizing the effects of pharmacological interventions versus placebo on depression (Baumeister et al., Fig. 7) is incorrect. The figure favours the placebo-control group instead of the experimental group, whereas none of the pharmacological studies (testing fluoxetine [2], paroxetine [3] and nortriptyline [4]) reported results in favour of the control condition. We believe that a correction should be published, as readers may easily misinterpret these key findings described in Fig. 7. In addition, Baumeister et al. conclude: ‘With regards to pharmacological interventions, selective serotonin reuptake inhibitors [seem] to be effective in reducing depressive symptoms’. However, in Fig. 6 of Baumeister et al., considerably larger effects in reducing depressive symptoms were reported for tricyclic antidepressants and a combination of selective serotonin reuptake inhibitors and benzodiazepines. Furthermore, the authors have inconsistently used the I statistic. Indeed, an I value > 75% can be considered as an indicator of high heterogeneity [5]. Heterogeneity for glycaemic control in psychological interventions was I = 82% in the short term and I = 78% in the medium term (Baumeister et al., Fig. 5) and thus results were not interpreted by the authors. However, depressive symptoms in psychological interventions (Baumeister et al., Fig. 3) showed even greater heterogeneity (I = 86% for the short term), yet these results were interpreted. This inconsistency has led to selective reporting of results. Finally, we are concerned about a secondary outcome measure of the study: health-related quality of life (HRQoL). This concept reflects ‘the extent to which one’s usual or expected physical, emotional, and social well-being are affected by a medical condition or its treatment’ [6]. In the study by Baumeister et al., no distinction is made between generic versus disease-specific questionnaires of HRQoL, which is reflected in the diversity of questionnaires used for measuring the concept of HRQoL (i.e. the Problem Areas In Diabetes (PAID) Questionnaire, Short Form-12 or 36 Health Survey (SF-12 or SF-36), Diabetes Symtom Checklist-Revised (DCS-R) and Diabetes-39 (D-39) questionnaire). We question whether these questionnaires all measure the same concept (HRQoL), as some are diabetes specific, whereas others are generic. We hold the opinion that no statements can be made about the concept of HRQoL if measured using such a diversity of questionnaires.