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People with psoriatic arthritis who had moderate or severe symptoms of depression were much less likely to reach a state where their disease was under good control or in remission after starting a new treatment that works throughout the body. This was the main finding of a study published in BMC Rheumatology, which analyzed data from Germany's RABBIT-SpA patient register. The link between depressive symptoms and treatment outcomes was found in both women and men. A statistical test found no clear evidence that the link was different between the sexes. The study included 2,139 patients who had joined the register since it began in May 2017. It adds a large amount of real-world patient data to growing evidence that mental health may be linked to how people with rheumatoid arthritis and psoriatic arthritis respond to treatment.

The RABBIT-SpA register collects information from patients treated at rheumatology clinics and medical practices across Germany. Patients join when they start a new treatment that works throughout the body. These treatments include biological drugs, targeted synthetic drugs, conventional synthetic disease-modifying antirheumatic drugs, and non-steroidal anti-inflammatory drugs. Doctors and patients complete forms when patients join, after three and six months, and then every six months for up to ten years. For this study, researchers included all patients with psoriatic arthritis who had joined by September 1, 2024, whose doctors had completed the starting assessment, and who had enough follow-up time to reach the six-month visit. The register contained 2,416 patients, but 277 had not yet reached six months of follow-up and were excluded. Of the remaining 2,139 patients, 251 did not have a valid score from the questionnaire used to assess depressive symptoms.

The researchers measured depressive symptoms using the WHO-5 Well-Being Index, a short questionnaire with five questions. Patients rate how often they feel cheerful, calm, active, well-rested, and interested in daily life. Answers range from never to all of the time. The scores are added together and multiplied by four to give a result from 0 to 100. Higher scores mean better well-being. Patients with scores below 29 were placed in the moderate or severe depressive symptoms group. Those scoring 29 or higher were placed in the group with no or mild depressive symptoms. Among the 1,888 patients with valid scores, 29 percent had moderate or severe depressive symptoms. The percentages differed between women and men: 34 percent of the 1,108 women and 23 percent of the 780 men were in this group.

At the start of the study, patients with moderate or severe depressive symptoms differed from those with no or mild symptoms in several ways. These differences were mostly similar in women and men. Patients with more depressive symptoms were less likely to take part in sports, were somewhat more likely to have obesity, and had much more active disease. More patients in this group had five or more tender joints, five or more swollen joints, or enthesitis, which is inflammation where tendons attach to bones. Their average DAPSA scores were about six to seven points higher in both sexes. DAPSA is a measure of disease activity that combines joint counts, patients' own assessments, and levels of C-reactive protein, a marker of inflammation. Patients with more depressive symptoms also had more other health conditions and used glucocorticoid medicines more often. Their reports of health and well-being were much worse, especially their reports of tiredness and the effect of the disease on their lives.

To study the link between well-being at the start and remission later, the researchers used a statistical method called logistic regression. They treated the WHO-5 score as a continuous measure and calculated how the odds of reaching a treatment goal changed with every 10-point increase in the score. They chose which other factors to account for using directed acyclic graphs. These diagrams show assumed cause-and-effect relationships and help researchers decide which factors to include in their calculations. Both statistical models accounted for sex, age, body mass index, participation in sports, previous use of advanced treatments, the number of other health conditions, how long symptoms had been present, and the type of treatment started. The model for minimal disease activity also accounted for the starting values of the measures used to define that outcome. The DAPSA model also accounted for the starting DAPSA score and related measures of disease activity. The researchers handled missing information using a method called multiple imputation with chained equations. This produced 50 complete datasets, and the results were combined using Rubin's rules. Additional analyses using only patients with observed WHO-5 scores gave very similar results.

After accounting for these other factors, each 10-point increase in well-being at the start was linked to higher odds of reaching minimal disease activity at six months. The odds ratio was 1.10. Higher well-being was also linked to higher odds of DAPSA remission at three months, with an odds ratio of 1.08, and at six months, with an odds ratio of 1.14. However, the link between well-being and minimal disease activity at three months just missed the usual threshold for statistical significance. Its odds ratio was 1.06, with a p-value of 0.051. The researchers also tested whether the relationship between well-being and treatment outcomes differed between women and men. They added a statistical term that measured this possible difference to their models. None of the four tests showed a statistically significant difference. All 95 percent confidence intervals included 1, and all p-values were at least 0.29. The authors explain that early results from separate analyses of women and men seemed to show a stronger relationship in women. However, finding a statistically significant result in one group and a non-significant result in another does not, by itself, prove that the relationship differs between the groups.

The researchers' descriptions of patients' progress over time showed a similar pattern. Among patients with no or mild depressive symptoms, 40 percent reached minimal disease activity at three months. A total of 29 percent maintained this state at both the three- and six-month visits, while another 14 percent first reached it by six months. Among patients with moderate or severe depressive symptoms, only 18 percent reached minimal disease activity at three months, 10 percent maintained it at both visits, and another 9 percent first reached it between three and six months. The pattern was seen in both sexes. Among women with no or mild symptoms, 34 percent reached minimal disease activity at three months and 22 percent maintained it at both visits. Among women with moderate or severe symptoms, the figures were 15 percent and 7 percent. For men, the corresponding figures were 47 percent and 37 percent in the no or mild symptoms group, compared with 24 percent and 17 percent in the moderate or severe symptoms group. Overall, women had lower rates of minimal disease activity than men, regardless of their level of depressive symptoms.

An important additional analysis made the results harder to interpret. The researchers replaced the combined measures of treatment success with measures based only on more objective findings. They used a swollen joint count of one or less instead of minimal disease activity, and normal C-reactive protein levels instead of DAPSA remission. With these alternative measures, well-being at the start was not linked to improvements in swollen joint counts at either follow-up visit. Higher well-being was also linked to a lower chance of having a normal C-reactive protein level at six months, with an odds ratio of 0.91. This suggests that the relationship with the combined measures of treatment success mainly came from their patient-reported parts, such as pain, patients' overall views of their health, and ability to function, rather than from clear improvements in inflammation measured by objective tests. The authors stress that their findings show a link between depressive symptoms and how patients experience and report their symptoms. They do not show that depressive symptoms affect the underlying inflammatory process of the disease.

The study has several limitations. The researchers did not formally diagnose depression. The WHO-5 is a screening questionnaire, not a tool that can confirm a diagnosis. Earlier analyses of the register also found that depression was often not recorded in medical records, even among patients with severe symptoms. The researchers also changed the standard definition of minimal disease activity to fit the information available in the register. They used body surface area instead of the psoriasis severity index and used cut-off points on a numerical rating scale instead of those on a visual analogue scale. This adapted definition has not been separately tested and validated. Well-being was measured only at the start of the study, even though depressive symptoms and disease activity may affect each other over time. Although the researchers adjusted for possible confounding factors identified using their causal diagrams, they could not rule out confounding by indication. This can happen when the reasons patients receive a particular treatment are also related to their outcomes. Patients with moderate or severe depressive symptoms differed from other patients in several ways at the start. The researchers also could not rule out the effects of other, unmeasured factors.

The authors conclude that doctors should consider routinely screening people with psoriatic arthritis for depressive symptoms. This could help identify patients who may be less likely to respond well to treatment and support a more complete approach to care that includes mental health. They suggest that timely referrals for psychological treatment or medicines could help improve mental health. However, this study did not show whether treating depressive symptoms would also improve responses to arthritis treatment. That question needs to be tested in studies that actively provide and evaluate treatments. The authors say future research should repeatedly measure both depressive symptoms and disease activity to understand how the two change over time and which may come first. They also recommend larger studies that combine data from several patient groups so researchers can more reliably test whether the relationship differs by sex. Finally, they call for randomized studies that test interventions and include disease activity or remission as secondary outcomes.

Subject of Research: The study examined the link between depressive symptoms and reaching remission in people with psoriatic arthritis who started a new treatment that works throughout the body. The researchers analyzed data from the RABBIT-SpA register.

Article Title: Depressive symptoms are associated with achieving remission in PsA patients – an analysis from the RABBIT-SpA register

Article References: Reich, A., Weiß, A., Lindner, L., Feuchtenberger, M., Dahmen, G., Lorenz, H.-M., Baraliakos, X., & Regierer, A. C. (2026). Depressive symptoms are associated with achieving remission in PsA patients – an analysis from the RABBIT-SpA register. BMC Rheumatology, 10(1), Article 79. https://doi.org/10.1186/s41927-026-00707-y

Image Credits: AI Generated

DOI: 10.1186/s41927-026-00707-y

Keywords: psoriatic arthritis, depressive symptoms, WHO-5 Well-Being Index, minimal disease activity, DAPSA remission, RABBIT-SpA register, sex differences, logistic regression, patient-reported outcomes, observational cohort, rheumatology, mental health