Assessment of Anhedonia in Adults With and Without Mental Illness: A Systematic Review and Meta-analysis.

This systematic review and meta-analysis assesses levels of anhedonia in healthy individuals and patients with mental illness according to the Snaith-Hamilton Pleasure Scale. Question Does anhedonia severity differ among patients with different types of mental illness typically associated with this symptom, and what is considered healthy hedonic functioning? Findings In this systematic review and meta-analysis of 168 studies including more than 16000 participants, anhedonia as measured by the Snaith-Hamilton Pleasure Scale was significantly elevated in patients with major depressive disorder, schizophrenia, substance use disorders, Parkinson disease, and chronic pain. Compared with ongoing major depressive disorder, all other patient groups displayed significantly lower anhedonia. Meaning The findings of this meta-analysis provide a possible set of reference values for anhedonia severity across healthy populations and those with mental illness; these results may have utility for researchers and clinicians evaluating new and existing treatments for anhedonia. Importance Anhedonia, a reduced capacity for pleasure, is described for many psychiatric and neurologic conditions. However, a decade after the Research Domain Criteria launch, whether anhedonia severity differs between diagnoses is still unclear. Reference values for hedonic capacity in healthy humans are also needed. Objective To generate and compare reference values for anhedonia levels in adults with and without mental illness. Data Sources Web of Science, Scopus, PubMed, and Google Scholar were used to list all articles from January 1, 1995 to July 2, 2019, citing the scale development report of a widely used anhedonia questionnaire, the Snaith-Hamilton Pleasure Scale (SHAPS). Searches were conducted from April 5 to 11, 2018, and on July 2, 2019. Study Selection Studies including healthy patients and those with a verified diagnosis, assessed at baseline or in a no-treatment condition with the complete 14-item SHAPS, were included in this preregistered meta-analysis. Data Extraction and Synthesis Random-effects models were used to calculate mean SHAPS scores and 95% CIs separately for healthy participants and patients with current major depressive disorder (MDD), past/remitted MDD, bipolar disorder, schizophrenia, substance use disorders, Parkinson disease, and chronic pain. SHAPS scores were compared between groups using meta-regression, and traditional effect size meta-analyses were conducted to estimate differences in SHAPS scores between healthy and patient samples. This study followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. Main Outcomes and Measures Self-reported anhedonia as measured by 2 different formats of the SHAPS (possible ranges, 0-14 and 14-56 points), with higher values on both scales indicating greater anhedonia symptoms. Results In the available literature (168 articles; 16494 participants; 8058 [49%] female participants; aged 13-72 years), patients with current MDD, schizophrenia, substance use disorder, Parkinson disease, and chronic pain scored higher on the SHAPS than healthy participants. Within the patient groups, those with current MDD scored considerably higher than all other groups. Patients with remitted MDD scored within the healthy range (g = 0.1). This pattern replicated across SHAPS scoring methods and was consistent across point estimate and effect size analyses. Conclusions and Relevance The findings of this meta-analysis indicate that the severity of anhedonia may differ across disorders associated with anhedonia. Whereas anhedonia in MDD affects multiple pleasure domains, patients with other conditions may experience decreased enjoyment of only a minority of life's many rewards. These findings have implications for psychiatric taxonomy development, where dimensional approaches are gaining attention. Moreover, the SHAPS reference values presented herein may be useful for researchers and clinicians assessing the efficacy of anhedonia treatments.