A total of 300 patients with psoriatic disease were analyzed, including 150 patients from the dermatology department and 150 patients from the rheumatology outpatient clinic. In total, 111 patients had skin psoriasis (Pso) and 189 psoriatic arthritis (PsA); 54% of patients were male and 46% were female. Mean age at assessment was 54.3 years and mean disease duration was 15.4 years. Mean age was higher (56.2 vs. 51.0 years, p = 0.005) in patients with PsA than in patients with Pso, but mean disease duration was shorter (14.0 vs. 17.4 years, p = 0.035). Furthermore, patients with PsA had a higher mean serum C-reactive protein (CRP) concentration compared to patients with Pso (p = 0.016). Epidemiological data are summarized in Table 1. Smoking was more prevalent in the skin psoriasis cohort (57.3% vs. 22.0%, p < 0.001). Mean BMI of both groups was within the overweight spectrum (28.2 vs. 27.6 kg/m2).

Regarding the educational level, 14.1% of patients had a university or polytechnic degree; 11.7% reported a high school diploma or polytechnic entrance qualification, whereas 71.5% reported lower secondary education or an intermediate school certificate as their highest educational degree; 2.7% of patients did not have a degree. There were no significant differences between patients with Pso and PsA regarding educational level.

At the time of assessment, 77.3% of patients had a systemic immunomodulatory therapy; 53.3% of patients were treated with a biological (b) disease-modifying antirheumatic drug (bDMARD), 7.7% with a targeted synthetic (ts) DMARD. A combination of b/tsDMARD with a conventional DMARD was used in 16% of patients. The most commonly used biologics in this cohort were interleukin (IL)-17 inhibitors (29.1%), followed by tumor necrosis factor (TNF) alpha inhibitors (18.3%) and IL-(12/)23 inhibitors (7.3%). Patients with PsA significantly more often had a biological therapy, a conventional synthetic (cs) DMARD therapy, and a combination therapy of b/tsDMARD + csDMARD (p = 0.001, p < 0.001, and p < 0.001, respectively). In the group of patients with Pso, 31.5% were treated with a topical therapy. Detailed numbers on therapies for both subgroups can be found in Table 1.

The queried patients with Pso reached on average 1.68 points in the PEST questionnaire compared to 3.72 points in the confirmed PsA cohort; 27.9% of patients with Pso scored ≥ 3 points, suspicious of psoriatic arthritis.

The great majority of patients in this cohort had multidomain disease: Only 21.6% of the included patients with Pso had only one single affected disease domain, whereas all included patients with PsA had at least two affected domains out of six possible disease domains (skin psoriasis, nail involvement, peripheral arthritis, axial disease, enthesitis, dactylitis). Patients with Pso had on average 2.88 affected domains (PEST ≥ 3, 4.84 domains; PEST < 3, 2.13 domains) compared to a mean of 4.61 affected domains in patients with PsA.

Of patients with Pso (PEST ≥ 3, 6.5%; PEST < 3, 0.0%), 1.8% had a clinically significant functional impairment in everyday life (FFbH < 60%) compared to 19.0% in the PsA cohort (p < 0.001). Of the queried patients with Pso, 73.9% reported peripheral and 25.2% reported axial joint pain with on average 3.39 of 21 joint regions affected. In the confirmed PsA cohort 96% of patients reported joint pain in on average of 8.39 joint regions (min 0, max 21), 94% had peripheral joint pain, and 60% complained of axial pain. The most commonly affected joint regions were the hands/fingers, followed by the knees, feet and toes, and lower back pain (Fig. 1). Patients with PsA scored significantly worse regarding their mobility and their ability to work than patients with Pso (p < 0.001, p = 0.013).

Joint distribution and affected disease domains. a Self-reported regions with joint pain or joint problems in psoriasis (n = 111) and psoriatic arthritis (n = 189). The most commonly affected regions were hands/fingers, knees, feet/toes, and lower back in patients with PsA; hands/fingers, feet/toes, lower back, and ankles in patients with Pso with a PEST score ≥ 3 (n = 31); knees, hands/fingers, and shoulders in patients with Pso with a PEST score < 3 (n = 80). b Number of affected disease domains (self-reported) out of six possible domains (skin psoriasis, nail involvement, peripheral arthritis, axial disease, enthesitis, dactylitis). PEST Psoriasis Epidemiology Screening Tool, PsA psoriatic arthritis, Pso psoriasis

In order to identify factors associated with relevant functional impairment, we performed logistic regression analysis. After adjustment for sex, disease duration, BMI, and smoking status, a diagnosis of PsA (odds ratio [OR] 9.56, p = 0.005), depressive symptoms (OR 5.44, p < 0.001), and age (OR 1.04, p = 0.033) were independently associated with relevant functional impairment in everyday life (Table 2).

Subjective overall quality of life did not differ significantly between patients with Pso and PsA. However, patients with PsA reached significantly lower scores in the physical health-related quality of life domain than patients with Pso (p < 0.001). In particular, patients with PsA reported more pain and malaise (p < 0.001) as well as more dependency on medication and support (p < 0.001). There were no significant differences between the two groups regarding overall mental health-related quality of life; however, patients with PsA scored worse than patients with Pso regarding energy and fatigue (p = 0.009) and more commonly reported sleeping problems and tiredness (both p = 0.001).

Patients with Pso who had a PEST score ≥ 3 rated their overall subjective quality of life significantly worse than patients with PEST score < 3 points (p = 0.003) and demonstrated a significantly reduced QoL in the health- and mental health-related domains as well as regarding their living environment (domains 1, 2, and 4; p < 0.001, p = 0.008, and p = 0.011, respectively) (see also Table 3 for comparison of PsA and Pso patients with PEST score  ≥ 3 and PEST score < 3). In particular, Pso patients with a PEST score ≥ 3  reported more pain, fatigue, and sleeping problems (p < 0.001, p = 0.002, and p = 0.010, respectively).

In general, patients less than 45 years of age reported a better subjective quality of life and a better health-related quality of life compared to patients aged over 45 years (p = 0.005, p < 0.001). Furthermore, subjective quality of life correlated significantly with educational level (p = 0.003).

In the PsA subgroup, female patients had a worse functional status than male patients as well as more joint regions with complaints (p = 0.019, p = 0.013). In contrast, in the Pso subgroup, there were no sex-related differences regarding the health-related quality of life or functional capacity.

Overall prevalence of depressive symptoms was high; 54% and 69% of the queried patients with Pso and PsA, respectively, showed at least mild depressive symptoms, and 19.8% of the patients with Pso and 30.1% of the patients with PsA had moderate to severe depressive symptoms (Fig. 2a). In contrast, only 17% of the patients had a history of depression from medical records or were taking antidepressants. A total of 10.6% of patients received antidepressant medication.

Depressive symptoms and quality of life. a Depressive symptoms determined by PHQ-9. Patients with PsA shown in dark blue, patients with Pso with PEST ≥ 3 in light blue, patients with Pso with PEST < 3 in white. b Pearson’s correlations between clinical data, quality of life, and depressive symptoms. Numbers within the graph represent Pearson’s R values. Red color indicates positive correlation, blue negative correlation. BMI body mass index, QoL quality of life, FFbH Functional Questionnaire Hannover, PEST Psoriasis Epidemiology Screening Tool, PHQ-9 Patient health questionnaire 9 (depressive symptoms), PsA psoriatic arthritis, Pso psoriasis, WHOQOL D1 World Health Organization Quality of Life Domain 1 (= physical health-related QoL), D2 = mental HRQoL, D3 = social QoL, D4 = environmental QoL

Patients with Pso with a PEST score ≥ 3 reached on average 8.68 points in the PHQ-9 depression questionnaire, equivalent to mild depressive symptoms, compared to 4.63 points in patients with Pso with a PEST score < 3 (within normal range) and 7.88 points in patients with PsA (ANOVA p < 0.0001). Significantly more depressive symptoms could be detected in patients with pain (p = 0.011) and functional impairment (p < 0.001). Depressive symptoms were highly negatively correlated with all domains of quality of life (p < 0.001; Fig. 2b). There were no significant differences between male and female patients regarding depressive symptoms.

In order to identify predictors of depression, a binomial logistic regression model was calculated using a stepwise backwards elimination approach and adjusting for demographic factors (age, sex, disease duration, BMI, smoking status). The model was statistically significant, χ2 (9) = 41.42, p < 0.001, classifying 75.1% of cases correctly. Functional impairment (OR 4.50, p < 0.003), axial complaints (OR 2.80, p = 0.030), diagnosis of psoriatic arthritis (OR 2.69, p = 0.046), and number of joint regions with complaints (OR 1.10, p = 0.032) were independently associated with moderate to severe depressive symptoms (Table 4). Separate models for PsA and Pso can be found in Supplemental Table 1.