Epidermal Penetration of Tape‐Stripping Differs Between Palmar and Dorsal Hand Skin: Implications for Biomarker Assessment in Chronic Hand Eczema

Tape-stripping is a minimally invasive skin sampling technique for assessment of epidermal biomarkers in inflammatory skin diseases and has been shown to capture the molecular signature of atopic dermatitis (AD) in line with data from skin biopsies [1]. Recently, tape-stripping was used to investigate biomarkers in chronic hand eczema (CHE) by transcriptomic and proteomic profiling [2-4]. However, no prior study has examined how deep tape-stripping penetrates the epidermis of palmar and dorsal hand skin. This information is essential for interpreting tape-strip biomarker data in CHE where lesions can be localised to both dorsal and palmar skin sites, potentially influencing the molecular signature. The study included eight CHE patients with palmar eczema and seven healthy controls (Table S1). Each participant had 0, 10, 30 and 50 serial tape strips (D-squame 2.2 cm2, Clinical and Derm) taken from the palmar and dorsal hand. Each tape was pressed against the skin for 10 s with standardised pressure (225 g/cm2), using the D-squame pressurizer (Clinical and Derm). For both palmar and dorsal regions, localisation for tape-stripping was randomised from a planned system to four adjacent skin areas (Figure S1). A reflectance confocal microscope (RCM) (Vivascope Multilaser 1500, Vivacope GmBH) was utilised, providing 6 × 6 mm en face mosaic images of the skin in 1–2 μm resolution. For both palmar and dorsal hand, the epidermal thickness of each test area, T0, T10, T30 and T50, was measured at three locations from the skin surface to the first visible papillae at the dermal-epidermal junction, and mean values were calculated. Removal of stratum corneum was visually evaluated by RCM (Figure S2), and transepidermal water loss (TEWL) (DermaLab, Cortex Technology) was measured at each test area. Paired permutation tests were used to test differences in epidermal thickness and TEWL after 10, 30 and 50 tape-strips compared with T0. Wilcoxon rank sum test was used to test significant differences between CHE patients and healthy. Spearman r correlation was used to analyse correlation between decrease in epidermal thickness and increase in TEWL. Written informed consent was obtained from all participants. The epidermal thickness without tape-stripping at T0 presented with large inter-individual and intra-individual differences within the same test area, particularly for palms (Figure 1, Table S2). For palmar skin, neither collection of 10, 30 or 50 consecutive tape-strips resulted in a significant decrease in epidermal thickness or increase in TEWL, and there was no correlation between the change in TEWL and epidermal thickness when data from all participants were pooled (Figure 1, Table S2). Furthermore, the stratum corneum was not removed after 50 tapes in any of the participants (Table S2). However, when considering CHE patients and healthy controls separately, CHE patients exhibited a significant decrease in epidermal thickness following 30 and 50 serial tape-strips (p = 0.04 and p = 0.02), and the epidermal thickness was significantly decreased in CHE patients compared to healthy participants (p = 0.03). Dorsal skin showed a significant decrease in epidermal thickness after 10, 30 and 50 tape-strips were collected compared to T0 for both CHE patients and for healthy controls (p < 0.001 for all participants pooled), which was accompanied by a significant increase in TEWL (p < 0.001) (Figure 1, Table S2). Decrease in epidermal thickness correlated with increase in TEWL (rho = −0.65, p < 0.001). In RCM images of dorsal hand, stratum corneum was completely removed in 3/8 (37.5%) CHE patients and 5/7 (71.4%) healthy controls. Only few previous studies have investigated how deep into the epidermis tape-stripping penetrates [5-7], and these studies showed that tape-stripping with 20–35 serial D-squame tape-strips removed most or all of stratum corneum reaching the upper granular layer. However, these prior studies sampled the forearm and included healthy controls and patients with AD. The finding that tape-stripping the palm did not completely remove stratum corneum in any of the participants despite 50 consecutive tape-strips, likely reflects the unique morphology of palmar skin with stratum lucidum and increased epidermal and stratum corneum thickness. Hence, when tape-stripping are used for biomarker profiling of palmar skin, researchers may consider using barrier/surgical tape which has been shown to remove more epidermal material compared to D-squame [6, 8]. For dorsal hand, the significant decrease in epidermal thickness and increase in TEWL is in line with previous studies outside of CHE, although stratum corneum was only removed in 8/15 participants compared to all participants in our previous study with a similar design [5]. This may suggest increased thickness of stratum corneum of dorsal hand skin compared to volar forearm skin, in line with prior studies [9]. Overall, our data on CHE patients align with findings on healthy controls. However, the significant decrease in palmar epidermal thickness exclusively in CHE patients may potentially reflect that palmar eczema decreases cohesion between corneocytes thereby increasing removal of stratum corneum by tape-stripping. Moreover, although not statistically significant, CHE patients exhibited lower palmar TEWL compared to controls, potentially reflecting the influence of hyperkeratotic lesions on TEWL. However, the limited number of participants and the significant age difference between healthy and CHE patients warrants caution when interpreting these data. Our study further showed large variation in epidermal thickness for each sample site even though the measurements were taken at immediately adjacent skin sites. This is in line with prior studies [10] showing great intraindividual variation of epidermal thickness of adjacent skin sites which reflects genuine topographical irregularity of the epidermis [10]. Our results indicate that this topographical irregularity is particularly large for palmar skin and has a greater impact on epidermal thickness than tape-stripping, explaining why the epidermal thickness of palmar skin appeared to be increased for some participants after serial tape-stripping. Accordingly, a same site approach might be beneficial, although RCM might affect subsequent tape-stripping. In conclusion, while our findings on dorsal hand skin tape-stripping are in line with previous studies, tape-stripping the palmar skin with D-squames did not remove stratum corneum or markedly decrease the epidermal thickness. Importantly, material from palmar tape-stripping originates from the superficial stratum corneum which may influence biomarker levels and should be considered when analysing biomarkers in CHE by tape-stripping. Mette Mogensen: resources, supervision, formal analysis, writing – review and editing. Yasemin Topal Yüksel: conceptualization, investigation, writing – original draft, methodology, data curation, formal analysis, writing – review and editing, visualization. Simon Francis Thomsen: writing – review and editing, methodology, investigation, project administration, supervision. Signe Bjørn: investigation, writing – review and editing, methodology. This research was funded by the Innovation Fund Denmark. M.O.C.: With no relation to this manuscript, Dr. Christensen has been a sub-investigator for LEO Pharma, paid consultant for LEO Pharma, and paid speaker for Pierre Fabre. S.F.T.: With no relation to the present manuscript, Dr. Thomsen has been a speaker or has served on advisory boards for Sanofi, AbbVie, LEO Pharma, Pfizer, Eli Lilly, Novartis, UCB Pharma, Union Therapeutics, Almirall, and Janssen Pharmaceuticals, and has received research support from Sanofi, Almirall, AbbVie, LEO Pharma, Novartis, UCB Pharma, and Janssen Pharmaceuticals. J.P.T.: An advisor for AbbVie, Almirall, Arena Pharmaceuticals, Coloplast, OM Pharma, Aslan Pharmaceuticals, Union Therapeutics, Eli Lilly & Co, LEO Pharma, Pfizer, Regeneron, and Sanofi-Genzyme, a speaker for AbbVie, Almirall, Eli Lilly & Co, LEO Pharma, Pfizer, Regeneron, and Sanofi-Genzyme, and received research grants from Pfizer, Regeneron, and Sanofi-Genzyme. Dr. Thyssen is a full-time employee at Leo Pharma. D.E.M.: A full-time employee at Leo Pharma. C.M.O.: Employed as industrial postdoc at LEO Pharma and Bispebjerg Hospital. The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions. Figure S1: Study design (A) Randomisation of sites for tape stripping. A, B, C and D mark the four sites for tape stripping, as well as TEWL and confocal microscopy. Site A corresponds to baseline with no tape-stripping, while 10, 30 and 50 tapes were taken from site B, C and D, respectively. Sixteen randomisation notes were prepared, each containing a full assignment of all four sample sites (T0, T10, T30, T50) across the four predefined anatomical localisations: thenar region, hypothenar region, distal to the thenar region, and distal to the hypothenar region. Each note specified the complete sampling configuration for a participant, ensuring that no participant received the same anatomical localisation for more than one intervention. Four notes placed T0 at the thenar region, 4 notes placed T0 at the hypothenar region, 4 notes placed T0 distal to the thenar region, and four notes placed T0 distal to the hypothenar region. Within each note, the remaining interventions (T10, T30, T50) were assigned to the other three anatomical sites using a clockwise rotation. The location for each participant was allocated by drawing localisation note from a box (8 for patients, and 8 for healthy). This approach ensured equal distribution of all four sampling interventions (T0, T10, T30, T50) across the four anatomical locations while preserving randomisation at the participant level. Figure S2: Visual assessment of removal of stratum corneum by RCM. RCM images at 6 μm depths after 0, 10, 30 and 50 tape-strips of dorsal hand skin in a healthy participant. (A + B) After 0 and 10 tape-strips, stratum corneum appears as a hyperreflective layer. (C) After 30 tape-strips, some areas present with a honeycomb pattern corresponding to stratum granulusom. (D) After 50 tape-strips, a honeycomb pattern are present at the entire surface, reflecting that stratum corneum is completely removed. Table S1: Demographics. Table S2: Epidermal thickness and transepidermal water loss following tape-stripping. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.