High-Frequency and Ultra-High-Frequency Ultrasound–Derived Skin Thickness Parameters as Objective Measures of Treatment Response in Adults with Plaque Psoriasis: A Systematic Review

Plaque psoriasis is a chronic immune-mediated inflammatory skin disease affecting 2–3% of the global population. Current clinical assessment tools—namely the Psoriasis Area and Severity Index (PASI), Physician Global Assessment (PGA), and Body Surface Area (BSA)—remain the standard for evaluating disease severity and treatment response. However, these instruments rely on clinician visual and tactile judgment, introducing well-documented interobserver variability and limited sensitivity to subclinical changes in disease activity. This creates a clear unmet need for objective, quantitative biomarkers that can complement existing clinical assessments and enable more precise, reproducible monitoring of therapeutic response. High-frequency ultrasound (HFUS, ≥20 MHz) and ultra-high-frequency ultrasound (UHFUS, >50 MHz) have emerged as promising noninvasive imaging modalities capable of visualizing the epidermis and dermis with axial resolution ranging from approximately 200 μm at 20 MHz to less than 30 μm at 70–100 MHz. In psoriatic plaques, these technologies reveal characteristic sonographic features, including a superficial hyperechoic band (thickened epidermis), a subepidermal low-echogenic band (SLEB) corresponding to acanthosis, papillary dermal edema, inflammatory infiltrate, and dilated vessels, and alterations in reticular dermal echogenicity. The SLEB, in particular, has been proposed as a sonographic hallmark of active psoriatic inflammation and a potential quantitative biomarker of disease severity. Despite growing interest in ultrasonographic monitoring of psoriasis, no systematic review has specifically focused on evaluating whether HFUS/UHFUS-derived skin thickness parameters can serve as objective, longitudinal measures of treatment response in plaque psoriasis. While broader reviews have addressed skin ultrasound applications in dermatology, the critical question of whether these parameters are responsive to treatment over time—and whether they correlate with established clinical endpoints—has not been systematically synthesized. This gap is clinically significant because the value of an imaging biomarker in chronic disease management lies not merely in its cross-sectional ability to characterize disease, but in its sensitivity to longitudinal change and its correspondence with treatment outcomes. The primary objective of this systematic review is to evaluate the available evidence on the use of HFUS/UHFUS-derived skin thickness parameters—specifically SLEB thickness, epidermal thickness, dermal thickness, and vascular signals as objective measures of treatment response in adults with plaque psoriasis. Secondary objectives include: (1) synthesizing the direction and magnitude of change in each ultrasound parameter during treatment; (2) evaluating the strength of correlation between ultrasound-derived parameters and established clinical severity scores; (3) characterizing measurement protocols, equipment, and technical approaches across studies to identify sources of heterogeneity; and (4) assessing the feasibility of quantitative synthesis (meta-analysis) based on the clinical and methodological characteristics of included studies. Methods This review follows PRISMA 2020 reporting guidelines and JBI methodology for evidence synthesis. A systematic search was conducted in PubMed/MEDLINE using a strategy combining three concept groups: ultrasound modality terms, ultrasound parameter terms, and disease/treatment terms. Eligible studies included adults with plaque psoriasis evaluated with HFUS (≥20 MHz) or UHFUS (>50 MHz), with longitudinal follow-up during treatment, reporting quantitative change in at least one ultrasound-derived skin thickness parameter. Study selection, data extraction, and risk of bias assessment (using an adapted Newcastle-Ottawa Scale) were performed systematically. Given anticipated heterogeneity, narrative synthesis was planned as the primary analytical approach, with evaluation of meta-analysis feasibility. Expected Outcomes Based on the review findings, four studies (comprising 75 patients and 228 lesions) met all eligibility criteria. The key expected outcomes of this project are: First, the review is expected to demonstrate that SLEB thickness is the most consistently responsive and clinically meaningful ultrasound biomarker for monitoring treatment response in plaque psoriasis, showing the earliest response (significant reductions within 2–4 weeks), the greatest magnitude of change (56–90% reduction across studies), and the strongest correlations with clinical severity scores (r values up to 0.96 for longitudinal change). Second, epidermal thickness (superficial hyperechoic band) is expected to show consistent but more modest reductions (25–54%) with weaker clinical correlations, reflecting the slower resolution of epidermal hyperproliferation compared to dermal inflammation. Third, Doppler-derived vascular signals are expected to emerge as a potentially sensitive early indicator of treatment efficacy, with reductions of 74–88% within 15–30 days, although this evidence is currently limited to a single study requiring independent validation. Fourth, the review is expected to identify substantial heterogeneity in ultrasound equipment (20–70 MHz), measurement protocols, and outcome reporting across studies, which precludes meta-analysis and underscores the urgent need for standardized measurement protocols. Finally, this project aims to provide a foundation for future research by identifying specific methodological priorities: development of consensus measurement protocols, larger multicenter studies with formal blinding and adequate statistical power, and head-to-head comparisons of HFUS/UHFUS parameters against established clinical endpoints (e.g., PASI 75/90/100) in the context of modern biologic therapies. These steps are essential to advance HFUS/UHFUS-derived parameters from promising research tools toward validated clinical endpoints for treatment monitoring in plaque psoriasis.