Patch test reactions through the lens of dermoscopy: Further insights, particularly on weak allergic reactions

Abstract

Background: Distinguishing weak allergic reactions from irritant patch test reactions may be difficult.Objectives: To describe the dermoscopic features of allergic reactions (especially weak allergic ones) and irritant patch test reactions, and to assess the suitability of dermoscopy in supporting differential diagnosis.Methods: Eligible participants for this observational, cross-sectional study included consecutive adult outpatients patch tested during a 12-month period, who developed any skin reaction. Healthy volunteers were patch tested with sodium lauryl sulfate as irritant controls. At the 72-hour reading, patch test reactions were recorded both with a digital camera and a digital dermoscopic system. For each reaction, clinical and dermoscopic variables were separately assessed, scored, and then compared.Results: Erythema, vessels, and vesiculation were constant dermoscopic features of allergic reactions (n = 173). In 46 weak (+) allergic reactions, dermoscopy showed (a) erythema (100%), (b) dense polymorphic vessels (100%), and (c) whitish vesicles (78.3%). Scores for vesicles and dotted vessels were significantly higher in weak allergic than in irritant reactions. Vesicles were identified as the chief dermoscopic parameter for correctly distinguishing weak allergic from irritant reactions.

Optical coherence tomography for patch test grading: A prospective study on its use for noninvasive diagnosis of allergic contact dermatitis

“…Since surgical biopsies are painful, expensive and time‐consuming, and histopathology does not always allow a precise distinction between contact allergic and irritant patch test reactions, various non‐invasive diagnostic techniques were used to further investigate patch test reactions experimentally 15,16,20‐23 . Dermoscopy is cheap and available worldwide; pilot studies correlated erythema, vesicles, orange‐yellowish patchy areas, and vessels with allergic reactions compared to irritant reactions; nonetheless, additional studies on doubtful reactions are needed 15,16 . Among further noninvasive diagnostic tools, RCM, OCT, and optoacoustic mesoscopy showed the most promising results 9‐14,24 .…”

“…Various diagnostic modalities have been investigated in attempts to overcome the subjectivity of patch test grading, and among them are laser Doppler velocimetry, transepidermal water loss, colorimetry, infrared thermography, 20‐MHz ultrasound A‐Scans, high‐definition optical coherence tomography, optoacoustic mesoscopy, dermoscopy, reflectance confocal microscopy (RCM) and conventional optical coherence tomography (OCT) 9‐16 . OCT is a noninvasive imaging technique that can differentiate skin structures, including the stratum corneum, the epidermis, the upper dermis, skin appendages, and blood vessels.…”

Contact dermato-allergology - review of the literature

“…Fanny Delcroix, Sonia-Cornelia Bădulici, Jean-François Nicolas : less intense erythema, fewer and less well-defined vesicles, isolated, orange crusts; irritative reactions to different allergens [C]: erythema and vessels less well represented than in allergic reactions, poral patterns, pustules, no vesicles; irritative reactions to SLS [D]: erythema, linear vessels, without poral patterns or pustules [4] The dermoscopic characteristics of allergic reactions to patch tests could help differentiate them from irritative reactions, as suggested by an article published by an Italian team in December 2019 [4]. In the study participated 139 patients tested with a baseline series, additional series and self brought products, as well as eleven healthy volunteers tested by Sodium Lauryl Sulfate (SLS).…”

“…The results are shown in Figure 3. Dermoscopy, by improving the visualization of the inflammatory process, can provide additional information especially on mild allergic reactions [4].…”

“…Figure 3. Extreme allergic reactions (+++) [A]: vesicles on erythematous background tend to coalesce, punctate vessels; mild allergic reactions (+) [B]: less intense erythema, fewer and less well-defined vesicles, isolated, orange crusts; irritative reactions to different allergens [C]: erythema and vessels less well represented than in allergic reactions, poral patterns, pustules, no vesicles; irritative reactions to SLS [D]: erythema, linear vessels, without poral patterns or pustules[4] …”