In this retrospective cohort study, data of ARPC patients were collected from The Eighth Affiliated Hospital of Sun Yat-sen University and Dermatology Hospital of Southern Medical University between December 2020 and December 2022. The study enrolled 10 ARPC patients who received dupilumab and 10 age-, sex-, and disease severity-matched ARPC patients who received conventional drugs. The ARPC patients were aged > 18 years and had umbilicated papules or nodules with a central adherent keratotic plug, as well as histopathological findings of elimination of necrotic basophilic collagen tissue into a cup‐shaped epidermal depression (3). We reviewed the medical records and photographs of patients, and to extracted data on demographic factors, comorbidities, lesion characteristics, histological and immunological findings, laboratory test results, treatments, responses to the initial treatment at 4 and 12 weeks, and adverse events (AEs) during the 12-week follow up. Missing data were obtained from patients by telephone. The study protocol was approved by the Ethics Committee and Institutional Review Board of the participating study centers. Written informed consent was obtained from the study participants.

The primary outcome was the W12 Investigator Global Assessment (IGA) score (0 or 1), and the secondary outcomes were the W4 IGA score (0 or 1), W4 numerical rating scale (NRS) score for itch (reduction ≥ 4 grades), and W12 NRS score for itch (reduction ≥ 4 grades). IGA 0 for ARCP was defined as the absence of umbilicated papules or nodules, while IGA1 was defined as having no more than 5 umbilicated papules or nodules in this study refering to the criteria for Investigator’s Global Assessment of Chronic Prurigo (16).The IGA rating was assessed by two dermatologists who are blinded to the patient’s enrollment status, basing on clinical photographs.

Immunohistochemistry was performed to detect lymphocyte subsets and Th2-related molecules in skin samples of 22 patients with ARPC, 5 patients with atopic dermatitis (AD), and 5 healthy controls (HCs).

Formalin-fixed, paraffin-embedded 3-µm tissue sections were prepared for immunohistochemical analysis. The sections were incubated with the following primary antibodies: anti-CD3 (DF6594; Affinity Biosciences, Cincinnati, OH, USA), anti-CD20 (DF13319; Affinity Biosciences), anti-T-bet (ab150440; Abcam, Cambridge, UK), anti-GATA3 (ab199428; Abcam), anti-IL-4 (66142-1-Ig; Proteintech, Chicago, IL, USA), and anti-IL-13 (CSB-PA011590LA01HU; Cusabio, Wuhan, China). A mouse and rabbit antibody kit (KIT9922; MXB, Fuzhou, China) was used for the detection of primary antibodies.

Stained sections were scanned using the Pannoramic Scan 150 device (3DHISTECH Ltd., Budapest, Hungary), to produce digital images (40× and 200× magnification) that were imported into the CaseViewer 2.4 (3DHISTECH Ltd.) image management system. ImageJ software (NIH, Bethesda, MD, USA) was used to analyze the images. The levels of IL-4, IL-13, and T- and B-cell markers in the dermis are expressed in terms of cellular density.

Immunofluorescence staining for the Th2-related markers GATA3, IL-4, and IL-13 was performed on skin samples from five ARPC patients, three AD patients, and two HCs.

The skin sections were deparaffinized on a hot plate at 65°C for 1 h and then blocked with donkey serum (10%; SL050-10; Solarbio, Beijing, China) for 30 min at room temperature. Double staining was performed with GATA3 (ab199428; Abcam), IL4 (66142-1-Ig; Proteintech), GATA3 (ab199428; Abcam), and IL13 (CSB-PA011590LA01HU; Cusabio). After incubation with the primary antibodies, skin biopsy specimens were incubated with the secondary antibodies Alexa Fluor™ 488 and 594 (Invitrogen, Carlsbad, CA, USA). The nuclei were counterstained with DAPI. The stained sections were scanned using the Pannoramic Scan 150 device (3DHISTECH Ltd.), to obtain digital images that were imported into the CaseViewer 2.4 (3DHISTECH Ltd.) image management system.

Normally distributed data are presented as means ± standard deviations (SDs). Student’s t-test and Fisher’s exact test were used to compare baseline variables between the groups. Primary and secondary outcomes were analyzed using Fisher’s exact test. Changes in IGA and NRS scores were analyzed using two-way repeated measures analysis of variance (ANOVA) and Tukey’s multiple comparison test. Immunohistochemical parameters are presented as means ± SDs, and were analyzed using one-way ANOVA and Tukey’s multiple comparison test. Student’s t-test, one-way ANOVA, and two-way repeated-measures ANOVA were performed using GraphPad Prism software (version 8.0.1; GraphPad Software Inc., San Diego, CA, USA). Fisher’s exact test was performed using SPSS software (version 25.0; IBM Corp., Armonk, NY, USA). P < 0.05 was considered indicative of statistical significance.

We divided 20 ARPC patients into dupilumab and conventional treatment groups. In the conventional treatment group, the patients received antihistamines and topical steroids; some patients also received thalidomide (n = 3) and narrowband ultraviolet B therapy (n = 1). Dupilumab was administered at an initial dose of 600 mg, followed by 2–12 doses of 300 mg every 2–4 weeks until symptomatic improvement was achieved. Table 1 presents the baseline characteristics of the study participants. Age, gender, and baseline disease severity did not show statistically significant differences between two groups. Regarding comorbidities, there were 6 cases combined with diabetes, 2 cases with renal disease, 2 cases with AD, and 2 cases with allergic rhinitis (AR) in the Dupilumab group. While, in the traditional treatment group, only 1 case was combined with diabetes. All 10 patients in dupilumab group had previously received and failed in responsing to traditional treatments, such as topical or oral medication, phototherapy with narrowband ultraviolet B.

In the dupilumab group, patients experienced satisfactory clinical improvement after treatment ( Table 2 ; Figure 1 ). At week 4, 3 (30%) of the 10 patients achieved an IGA score of 0 or 1, and 6 (60%) achieved a significant reduction (≥ 4 grades) in the NRS score for itch (mean decrease of 4.1 [from 7.6 to 3.5]). At week 12, all ten patients had achieved complete clearance of their skin lesions, and nine of ten (90%) achieved relief from pruritus, only one patient had slight itching, with a NRS score of 1. In the conventional group, no patient achieved an IGA score 0 or 1 at week 4 or 12 ( Figure 2 ). Only 1 (10%) of the 10 patients in the conventional group achieved a significant reduction in the NRS score at 12 weeks; the mean NRS scores at baseline, week 4, and week 12 were 6.5, 5.3, and 4.4, respectively ( Figure 2 ). We also conducted a statistical analysis excluding 4 patients with allergic diseases (2 cases with AD and 2 cases with AR), and the results are shown in Table 3 . The most common AE was lethargy.

AEs were more common in the conventional group (3/10) than dupilumab group (no AEs) during the 12 weeks of treatment. In the conventional group, two patients experienced lethargy and one experienced limb numbness.

Immunohistochemical staining was performed to analyze lymphocyte subsets in skin samples from ARPC patients, AD patients, and HCs. In AD samples, CD3+ cells were localized mainly in the superficial and mid dermis, whereas in ARPC samples CD3+ cells had infiltrated the entire dermis and subcutaneous tissue. The T-cell density in the dermis of ARPC was similar to that in AD and significantly higher than that in HCs (p = 0.0039 and = 0.0009, respectively; Figure 3 ). There were no significant differences among the groups in terms of CD20+ cell density. The skin samples were stained with T-bet and GATA3, which are the transcription factors of Th1 and Th2 cells, respectively. The GATA3+ cell density in the ARPC group was similar to that in the AD group and significantly higher than that in HCs (p = 0.0183 and = 0.0316, respectively). There were no significant differences among the groups in terms of T-bet+ cell infiltration. These results suggest a predominance of Th2 cells over Th1 cells in ARPC, similar to AD.

The expression of Th2-associated cytokines, including IL-4 and IL-13, was analyzed by immunohistochemical staining of the ARPC, AD, and HC skin samples. The IL-4+ cell density was significantly higher in the ARPC and AD groups than in HCs (p = 0.0093 and = 0.0047, respectively) ( Figure 4 ). Similarly, IL-13 overexpression was also observed in the ARPC and AD groups compared to HCs (p = 0.0002 and = 0.0066, respectively). Multi-immunofluorescence staining analysis suggested that IL-4 and IL-13 were co-expressed with the Th2 transcription factor GATA3 in ARCP and AD samples, suggesting that IL-4 and IL-13 were derived from GATA3+ Th2 cells in ARCP, similar to AD ( Figure 5 ).