The 5-D Itch Scale Explains Sleep Impairment Beyond Visual Analogue Scale in Psoriasis: A Cross-Sectional Case-Control Study

1. Introduction

Psoriasis is a chronic, immune-mediated inflammatory skin disease affecting approximately 2–3% of the global population and is increasingly recognized as a systemic disorder with physical, psychological, and social consequences [1,2]. Beyond skin lesions, pruritus, sleep disturbances, and mood disorders impair quality of life and may perpetuate disease activity through stress-mediated pathways [3,4,5,6].

Pruritus affects 60–90% of patients with psoriasis [5] and is often underappreciated despite its effects on functioning, psychological well-being, and sleep [7,8]. It commonly intensifies at night, disrupting sleep through the itch–scratch–wake cycle, possibly because of circadian changes in skin barrier function and cortisol levels [8,9,10].

Sleep disturbances affect 50–75% of patients with psoriasis, with PSQI studies consistently showing poorer sleep than in controls [9,10,11,12,13]. Impaired sleep is associated with immune dysregulation and cardiometabolic risk [14,15]. Depression affects up to 30% of patients and is independently associated with pruritus and sleep impairment [16,17,18], suggesting a self-reinforcing cycle.

The interplay among pruritus, sleep quality, depression, and disease severity remains incompletely characterized. Most controlled studies use unidimensional scales such as VAS, which measures intensity but not temporal pattern, functional impact, or anatomical distribution [19]. Few studies have used the 5-D Itch Scale with sleep measures in psoriasis [11], and none has directly compared a multidimensional instrument with a unidimensional tool for sleep outcomes within the same regression framework. Data from Middle Eastern and Mediterranean populations and matched-control studies evaluating all four domains remain limited [9,12].

This study aimed to compare sleep quality, depressive symptoms, and dermatology-specific quality of life between patients with psoriasis and clinic-based controls; identify independent predictors of sleep impairment; and compare the explanatory value of the 5-D Itch Scale and VAS.

2. Materials and Methods

2.1. Study Design and Setting

This cross-sectional case-control study was conducted at a university hospital between February 2023 and April 2024 and was reported according to the STROBE guidelines [20]. The institutional Non-Interventional Research Ethics Committee approved the study, which was conducted in accordance with the Declaration of Helsinki. Written informed consent was obtained from all participants prior to enrolment.

2.2. Participants

The psoriasis group comprised 63 consecutive adults (≥18 years) with clinically and/or histopathologically confirmed psoriasis recruited during outpatient follow-up. Controls were 63 age- and sex-frequency-matched individuals evaluated for benign melanocytic naevi, without psoriasis or other chronic pruritic or inflammatory dermatoses.

Exclusion criteria were age <18 years, inability to consent, cognitive impairment preventing questionnaire completion, chronic pruritic conditions other than psoriasis, and use of antidepressant, anxiolytic, or hypnotic medication. Sample size was estimated from previous PSQI studies [9,14]. Assuming a 2.0-point between-group difference in global PSQI (SD≈3.5), two-sided α=0.05, and 80% power, an independent-samples t-test required 50 participants per group. We enrolled 63 per group to improve precision.

2.3. Clinical and Psychometric Assessment

Participants completed the following validated instruments:

Dermatology Life Quality Index (DLQI): A 10-item dermatology-specific quality-of-life instrument categorized as no (0–1), small (2–5), moderate (6–10), very large (11–20), or extremely large (21–30) effect [21]. The validated Turkish version was used [22].

Beck Depression Inventory (BDI): A 21-item self-report measure of depressive symptom severity (0–63; higher scores indicate greater severity) [23]. The validated Turkish version was used [24], with BDI ≥10 defining clinically meaningful symptom burden.

Pittsburgh Sleep Quality Index (PSQI): A 19-item instrument assessing seven sleep components over the preceding month (0–21; global score ≥5 indicates poor sleep quality) [25]. The validated Turkish version was used [26].

Psoriasis Area and Severity Index (PASI): A single dermatologist assessed disease severity (0–72) [27].

5-D Itch Scale: A multidimensional measure of duration, degree, direction, disability, and distribution (5–25; higher scores indicate more severe itch) [28]. The validated Turkish version was used [29].

Visual Analogue Scale (VAS) for Pruritus: A 10-cm scale (0=no itch; 10=worst imaginable) assessing lifetime worst and preceding-three-day pruritus [30], categorized as mild (1–3), moderate (4–6), severe (7–8), or very severe (9–10).

2.4. Statistical Analysis

Normality was assessed using the Shapiro–Wilk test, histograms, and Q–Q plots, and variance homogeneity using Levene's test. Continuous variables were compared by independent-samples t-test or Mann–Whitney U test, as appropriate. Categorical variables were compared by Pearson's chi-square or Fisher's exact test when expected counts were <5. Spearman correlations were interpreted as weak (r<0.30), moderate (r=0.30–0.49), or strong (r≥0.50) [31]. Rank-biserial correlations quantified between-group effect sizes.

Within the psoriasis group (n=63), multivariable linear regression identified independent predictors of global PSQI. Model 1 included the 5-D Itch Scale, BDI, PASI, BMI, and smoking status (ever vs never); Model 2 substituted lifetime VAS for the 5-D Itch Scale. We report unstandardized coefficients (B), standard errors, standardized β, 95% confidence intervals, and p-values. VIF >5 indicated problematic multicollinearity; residual normality was assessed by Shapiro–Wilk testing.

Hierarchical regression compared the explanatory value of the 5-D Itch Scale and VAS. Step 1 included BDI, PASI, BMI, and smoking; Step 2 added VAS (2a) or the 5-D Itch Scale (2b); Step 3 added the 5-D Itch Scale after VAS. Incremental contributions were assessed by ΔR² and F-change tests.

Analyses used R version 4.3.2 (R Foundation for Statistical Computing, Vienna, Austria), with two-sided p<0.05 considered significant.

3. Results

3.1. Sociodemographic and Clinical Characteristics

The 126 participants comprised 63 patients and 63 controls. Groups were comparable in age, sex, marital status, education, and socioeconomic status (all p > 0.05; Table 1). Patients had higher BMI (28.6 ± 5.4 vs. 26.2 ± 2.7 kg/m²; p = 0.002) and were more often current smokers (36.5% vs. 15.9%; p = 0.004). Alcohol use did not differ (p = 0.466).

Dyslipidemia (68.3% vs. 25.4%; p < 0.001) and hepatosteatosis (55.6% vs. 6.3%; p < 0.001) were more prevalent in the psoriasis group. Other comorbidities did not differ (all p > 0.05; Table 2).

3.2. Disease Characteristics of the Psoriasis Group

Median age at diagnosis was 33 years (interquartile range [IQR]: 20–49), disease duration 12 years (IQR: 3–21), and PASI 4.8 (IQR: 2.4–8.6), indicating predominantly mild-to-moderate activity. All patients had received topical corticosteroids and 95.2% topical vitamin D analogues. Treatments included methotrexate (65.1%), biologics (39.7%), systemic retinoids (23.8%), cyclosporine (11.1%), and phototherapy (19.0%).

3.3. Pruritus Characteristics

The 5-D Itch Scale identified pruritus in 87.3% (55/63) of patients. Lifetime VAS classified 63.5% as severe or very severe (33.3% and 30.2%, respectively), 27.0% as moderate, and 9.5% as mild. Median lifetime VAS was 8.0 (IQR: 5.0–9.0) versus 3.0 (IQR: 1.0–5.0) over the preceding three days, likely reflecting treatment effects.

The 5-D disability subscale correlated strongly with PSQI (r = 0.556), BDI (r = 0.561), DLQI (r = 0.540), and PASI (r = 0.588; all p < 0.01). The distribution subscale correlated most strongly with PASI (r = 0.690, p < 0.01). The scalp and lower legs were most commonly affected (both 52.4%), followed by the thighs (49.2%), buttocks and forearms (both 41.3%), and back (33.3%).

3.4. Quality of Life, Depression, and Sleep Quality

Patients had greater quality-of-life impairment, depressive symptom scores, and sleep impairment than controls (Table 3). Median DLQI was 15.0 (IQR: 9.0–23.0) versus 2.0 (IQR: 0.0–3.0; p < 0.001; rank-biserial r = −0.950), with 73.0% of patients reporting clinically meaningful impairment (DLQI > 10).

Clinically meaningful depressive symptoms (BDI ≥ 10) occurred in 46.0% of patients versus 12.7% of controls. Median BDI was 8.0 (IQR: 3.0–15.0) versus 6.0 (IQR: 3.0–8.0; p = 0.015; rank-biserial r = −0.251).

Poor sleep quality (PSQI ≥ 5) was identified in 58.7% of patients vs. 36.5% of controls. Global PSQI scores were significantly higher in the psoriasis group (6.0 [IQR: 3.0–10.0] vs. 4.0 [IQR: 3.0–5.0]; p = 0.001; rank-biserial r = −0.331). Among PSQI components, patients with psoriasis scored significantly worse on subjective sleep quality (p = 0.014), sleep latency (p = 0.014), habitual sleep efficiency (p = 0.029), sleep disturbances (p = 0.001), and daytime dysfunction (p = 0.002). Sleep duration and use of sleep medication did not differ (both p > 0.05).

3.5. Correlations Among Study Variables

Spearman correlation analysis in the psoriasis group showed that global PSQI scores correlated strongly with BDI (r = 0.685, p < 0.01) and moderately with DLQI (r = 0.485, p < 0.01), the 5-D Itch Scale (r = 0.483, p < 0.01), and PASI (r = 0.375, p < 0.01; Table 4).

Total 5-D Itch Scale scores correlated strongly with PASI (r = 0.718, p < 0.01) and moderately with PSQI (r = 0.483), DLQI (r = 0.435), and BDI (r = 0.330; all p < 0.01). PASI also correlated with DLQI (r = 0.586, p < 0.01) and BDI (r = 0.355, p < 0.01).

3.6. Multivariable Regression Analysis

Model 1, including the 5-D Itch Scale, BDI, PASI, BMI, and smoking status, was significant (F(5, 57) = 19.52, p < 0.001) and explained 63.1% of PSQI variance (adjusted R² = 0.599). BDI was the strongest independent predictor (B = 0.335, β = 0.643, 95% CI [0.240, 0.430], p < 0.001), followed by the 5-D Itch Scale (B = 0.367, β = 0.315, 95% CI [0.137, 0.596], p = 0.002). PASI (p = 0.446), BMI (p = 0.277), and smoking (p = 0.124) were not independently associated with PSQI. All VIF values were ≤ 1.60, and residuals were approximately normal (Shapiro–Wilk W = 0.993, p = 0.976; Table 5).

In Model 2, in which lifetime VAS was substituted for the 5-D Itch Scale, the model remained significant (F(5, 57) = 15.16, p < 0.001) but explained less variance (R² = 0.571, adjusted R² = 0.533). VAS was not a significant independent predictor of PSQI (B = 0.141, β = 0.080, 95% CI [−0.186, 0.468], p = 0.391). Only BDI retained significance (β = 0.695, p < 0.001; Table 5).

3.7. Hierarchical Regression: 5-D Itch Scale Versus VAS

Hierarchical regression formally compared the explanatory value of the 5-D Itch Scale and VAS (Table 6). The base model (BDI, PASI, BMI, and smoking) explained 56.5% of PSQI variance (R² = 0.565). Adding VAS (Step 2a) did not improve fit (ΔR² = 0.006, F-change = 0.746, p = 0.391), whereas adding the 5-D Itch Scale (Step 2b) did (ΔR² = 0.066, F-change = 10.245, p = 0.002). When added after VAS (Step 3), the 5-D Itch Scale still explained significant additional variance (ΔR² = 0.064, F-change = 9.782, p = 0.003). The 5-D Itch Scale therefore accounted for PSQI variance that VAS intensity alone did not explain.

4. Discussion

This study provides a comprehensive assessment of the interrelationships among pruritus, sleep quality, depression, and quality of life in patients with psoriasis compared with matched controls. Our findings demonstrate that patients with psoriasis exhibit significantly impaired sleep quality, greater depressive symptom burden, and substantially reduced quality of life. Multivariable regression analysis identified depression and pruritus — assessed using the multidimensional 5-D Itch Scale — as the only independent predictors of sleep impairment after adjustment for disease severity, BMI, and smoking status.

Pruritus was reported by 87.3% of patients in our cohort, consistent with the 60–90% prevalence range reported in the literature [5,7,8]. The median lifetime VAS of 8.0 indicates that the majority of patients had experienced severe pruritus at some point during their disease course. The large discrepancy between lifetime (8.0) and current (3.0) VAS scores in our study likely reflects the effect of ongoing treatment.

A notable finding was the strong correlation between 5-D Itch Scale scores and PASI (r=0.718), indicating that pruritus intensity in our cohort closely paralleled clinical disease severity. While some studies have reported weaker or absent associations between pruritus and objective disease severity [9,32], our use of the 5-D Itch Scale — a multidimensional instrument capturing distribution, disability, and temporal pattern in addition to intensity — may explain this stronger association, as PASI inherently reflects both extent and severity across body regions. However, this strong correlation also raises the possibility of measurement overlap between the distribution subdomain of the 5-D Itch Scale and the anatomical extent component of PASI; the low VIF values (1.50 for the 5-D Itch Scale, 1.60 for PASI) in our regression model suggest that this overlap did not introduce problematic collinearity.

Poor sleep quality affected 58.7% of patients with psoriasis, compared with 36.5% of controls. This prevalence is consistent with the 53.6% reported by Jensen et al. [9] and the 59% reported by Sahin et al. [12], and substantially lower than the 76.3% found by Henry et al. among self-selected survey respondents [11], likely reflecting methodological heterogeneity across studies.

The multivariable regression analysis represents the principal analytical advance of this study. BDI was the strongest independent predictor of PSQI (β=0.643), consistent with the findings of Jensen et al. [9] and Sahin et al. [12], who similarly identified depressive symptoms as the dominant predictor of sleep impairment in psoriasis using multivariate methods. The 5-D Itch Scale was the second independent predictor (β=0.315), indicating that pruritus burden contributes to sleep impairment beyond what is explained by depression, disease severity, BMI, or smoking status. Importantly, PASI was not independently associated with PSQI after adjustment for other covariates, suggesting that symptom burden — particularly pruritus and depression — may be more relevant to sleep outcomes than clinician-assessed disease severity. This finding aligns with prior observations that PASI correlates inconsistently with patient-reported outcomes [9,10,11,32].

The hierarchical regression analysis directly addressed whether the 5-D Itch Scale provides explanatory value beyond the VAS. When added to a base model containing BDI, PASI, BMI, and smoking, VAS did not significantly improve model fit (ΔR²=0.006, p=0.391), whereas the 5-D Itch Scale did (ΔR²=0.066, p=0.002). Even after VAS had been entered, the 5-D Itch Scale continued to explain significant additional variance (ΔR²=0.064, p=0.003). These results suggest that the functional and distributional dimensions of pruritus captured by the 5-D Itch Scale — including nocturnal itch-related disability, interference with daily activities, and anatomical spread — contribute to sleep impairment in ways that a unidimensional intensity rating does not reflect. This observation has practical implications: in both clinical trials and routine practice, relying solely on VAS may underestimate the sleep-relevant burden of pruritus in psoriasis.

Pruritus was moderately correlated with global PSQI scores (r=0.483) and specific components including sleep disturbances and daytime dysfunction, aligning with previous reports identifying itch as a key contributor to poor sleep in psoriasis [8,9,11,12]. The association is biologically plausible: pruritus in psoriasis exhibits circadian variation, with nocturnal exacerbation attributed to decreases in cortisol levels, increases in trans epidermal water loss, and changes in skin temperature [9,10].

The strong depression–sleep association observed in both bivariate (r=0.685) and multivariable analyses (β=0.643) may reflect shared neurobiological pathways. Pro-inflammatory cytokines central to psoriasis pathogenesis — including tumor necrosis factor-α, interleukin-6, and interleukin-17 — have been implicated in dysregulation of sleep architecture and in depression through effects on serotonergic neurotransmission and HPA axis activity [15,18]. It should also be noted that the BDI contains somatic items related to fatigue, sleep disturbance, and loss of energy that overlap conceptually with PSQI items, which may contribute to the strength of this association. Future studies using the BDI cognitive-affective subscale separately could help distinguish shared construct variance from genuine comorbidity.

Although the correlation between pruritus severity and depression was weaker (r=0.330), it remained significant, suggesting that pruritus contributes to depressive symptoms but does not fully account for them. Other factors — including stigmatization, body image concerns, and social withdrawal — likely contribute independently to depressive symptomatology in psoriasis [6,13,18,33]. Whether depression mediates the relationship between pruritus and sleep impairment, as suggested by Sahin et al. [12], could not be determined from our cross-sectional data and warrants investigation in future longitudinal studies.

Quality of life was severely impaired in patients with psoriasis (median DLQI 15.0), corresponding to a "very large effect" per the established DLQI banding system [34]. The finding that 73% of patients had clinically meaningful DLQI impairment underscores the profound psychosocial burden of the disease, even in a cohort receiving active treatment.

This study has several strengths. The simultaneous evaluation of pruritus, sleep quality, depression, and quality of life using validated instruments within a single matched-control design enabled a comprehensive assessment of their interrelationships. The inclusion of multivariable regression adjusting for BMI, smoking status, PASI, and depressive symptoms addresses a limitation of most prior studies in this area, which relied primarily on bivariate analyses. The hierarchical regression directly comparing the 5-D Itch Scale against VAS as predictors of PSQI scores represents, to our knowledge, the first formal head-to-head comparison of these pruritus instruments for sleep outcomes in psoriasis. Additionally, the inclusion of sociodemographic ally matched controls strengthens the internal validity of between-group comparisons.

These findings carry direct clinical implications. In routine dermatological practice, incorporating the 5-D Itch Scale alongside or in place of VAS for pruritus assessment may capture sleep-relevant dimensions of itch that intensity-only measures miss, enabling more targeted management of sleep impairment. Systematic screening for depressive symptoms using validated instruments such as the BDI should be integrated into psoriasis care pathways, given that depression was the strongest independent predictor of poor sleep quality in this cohort. Furthermore, clinicians should recognize that patient-reported symptom burden — particularly pruritus and depression — may be more relevant to sleep outcomes than clinician-assessed disease severity (PASI), reinforcing the importance of patient-centered outcome assessment in psoriasis management.

Several limitations should be noted. First, the cross-sectional design precludes causal inference; all reported associations are correlational. Second, the study was conducted at a single tertiary referral center, and the high rates of systemic and biologic therapy use may limit generalizability to patients managed in primary care settings. Third, sleep quality was assessed by subjective self-report (PSQI) without objective measures such as polysomnography or actigraphy. Fourth, anxiety was not assessed; given that prior studies [9,12] have identified anxiety as an independent predictor of sleep disturbance in psoriasis, its omission may represent a source of residual confounding.

5. Conclusions

Depression and pruritus are independently associated with sleep impairment in patients with psoriasis after adjustment for disease severity, BMI, and smoking status. The 5-D Itch Scale explains significant additional variance in sleep quality beyond that captured by the VAS, indicating that the functional, distributional, and temporal dimensions of pruritus contribute to sleep impairment in ways that intensity alone does not reflect. These findings support the integration of multidimensional pruritus assessment and systematic depression screening into routine dermatological care for patients with psoriasis. Future longitudinal studies with objective sleep measures, anxiety assessment, and mediation analyses are needed to elucidate the temporal and causal relationships among these interconnected domains.