Reflectance confocal microscopy (RCM) allows real-time, noninvasive microscopic view of the skin at nearly histologic resolution serially over time. RCM increases the sensibility and sensitivity of the diagnosis of skin tumours. RCM evaluates descriptive features of psoriasis, lupus erythematosus, contact dermatitis, and others. Three groups of optical histology have been described: psoriasiform, spongiotic, and interface dermatitis. In a multicenter study, RCM patterns of spongiotic, hyperkeratotic, and interface dermatitis have been analyzed and an algorithmic method of analysis for fast application in the clinical setting based on a multivariate analysis has been proposed. A tree decision diagram has been also established.
Key points
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Reflectance confocal microscopy (RCM) is a relatively novel noninvasive tool for microscopic evaluation of the skin recently applied on inflammatory skin conditions.
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RCM features useful for the differentiation between the 3 main inflammatory diseases groups, psoriasiform, spongiotic, and interface dermatitis, have been described.
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Algorithmic method of analysis for clinical fast application based on a multivariate analysis has been proposed.
Introduction
In vivo reflectance confocal microscopy (RCM) is an imaging technique that allows a real-time, microscopic view of the skin with cellular-level resolution close to conventional histopathological analysis. RCM provides “virtual” skin biopsies offering microscopic details of the different skin layers with an en face view.
RCM has been applied to the clinical setting for diagnosis and decision management of several inflammatory, neoplastic, and melanocytic skin diseases. In dermatooncology, this technique is considered as a second-level examination positioned after dermoscopic examination in the clinical routine.
Recent prospective studies demonstrated that RCM improves diagnostic accuracy and spares numerous unnecessary surgical excisions. Moreover, thanks to the possibility of detailed microscopic changes observation, RCM has been adopted for in vivo evaluation of therapeutic follow-up and diseases progression.
More recently, starting from the description of the confocal microscopic patterns, RCM has been also applied on inflammatory skin conditions such as contact dermatitis, psoriasis, discoid lupus erythematosus, lichen planus, and seborrheic dermatitis demonstrating high confocal–histology correlation. Consequently, the potential applicability of RCM to the diagnosis and differential diagnosis of inflammatory skin diseases has been proposed, but the effective practical usefulness of RCM in the clinical practice still remained debated because a practical methodology for clinical routine is still lacking and, furthermore, a limited number of cases has been evaluated in different studies.
Similar to the approach used in histopathology, the identification of spongiosis, hyperkeratosis, and interface changes as seen on RCM permits to classify inflammatory skin diseases into 3 main groups: psoriasiform dermatitis, interface dermatitis, and spongiotic dermatitis. Later, additional disease-specific confocal features have been also demonstrated to be identifiable with RCM. The open issue was still related to the demonstration of an effective practical application of RCM in the real-life clinical setting for the diagnosis of distinct inflammatory skin diseases. To address this issue, more recently, a multicentric study designed and executed under the supervision of the International Confocal Group has been conducted with the aim of the identification of specific confocal features useful for the distinction between the 3 main groups of inflammatory skin diseases. The study was conducted on a large number of cases affected by different superficial inflammatory skin diseases representing the different groups of entities. A multivariate model of prediction of individual case probability of diagnosis was built and applied to identify the significant confocal criteria describing each group of disease. The defined collection of confocal features have been translated into a diagnostic algorithm for practical application of RCM to the differentiation of the groups and later a tree diagram has been also proposed for a schematic and simplified analysis of confocal examinations.
Introduction
In vivo reflectance confocal microscopy (RCM) is an imaging technique that allows a real-time, microscopic view of the skin with cellular-level resolution close to conventional histopathological analysis. RCM provides “virtual” skin biopsies offering microscopic details of the different skin layers with an en face view.
RCM has been applied to the clinical setting for diagnosis and decision management of several inflammatory, neoplastic, and melanocytic skin diseases. In dermatooncology, this technique is considered as a second-level examination positioned after dermoscopic examination in the clinical routine.
Recent prospective studies demonstrated that RCM improves diagnostic accuracy and spares numerous unnecessary surgical excisions. Moreover, thanks to the possibility of detailed microscopic changes observation, RCM has been adopted for in vivo evaluation of therapeutic follow-up and diseases progression.
More recently, starting from the description of the confocal microscopic patterns, RCM has been also applied on inflammatory skin conditions such as contact dermatitis, psoriasis, discoid lupus erythematosus, lichen planus, and seborrheic dermatitis demonstrating high confocal–histology correlation. Consequently, the potential applicability of RCM to the diagnosis and differential diagnosis of inflammatory skin diseases has been proposed, but the effective practical usefulness of RCM in the clinical practice still remained debated because a practical methodology for clinical routine is still lacking and, furthermore, a limited number of cases has been evaluated in different studies.
Similar to the approach used in histopathology, the identification of spongiosis, hyperkeratosis, and interface changes as seen on RCM permits to classify inflammatory skin diseases into 3 main groups: psoriasiform dermatitis, interface dermatitis, and spongiotic dermatitis. Later, additional disease-specific confocal features have been also demonstrated to be identifiable with RCM. The open issue was still related to the demonstration of an effective practical application of RCM in the real-life clinical setting for the diagnosis of distinct inflammatory skin diseases. To address this issue, more recently, a multicentric study designed and executed under the supervision of the International Confocal Group has been conducted with the aim of the identification of specific confocal features useful for the distinction between the 3 main groups of inflammatory skin diseases. The study was conducted on a large number of cases affected by different superficial inflammatory skin diseases representing the different groups of entities. A multivariate model of prediction of individual case probability of diagnosis was built and applied to identify the significant confocal criteria describing each group of disease. The defined collection of confocal features have been translated into a diagnostic algorithm for practical application of RCM to the differentiation of the groups and later a tree diagram has been also proposed for a schematic and simplified analysis of confocal examinations.
Spongiotic dermatitis
Spongiotic dermatitis are microscopically characterized by the presence of intercellular and/or intracellular edema at epidermal level associated with prevalence of inflammatory cells between keratinocytes and perivascular infiltration in the upper dermis. The prototype of this group of inflammatory skin diseases is irritant and allergic contact dermatitis. The presence of moderate to severe spongiosis and/or detection of vesicles are considered as the main findings characterizing those entities distinguishing spongiotic dermatitis from interface and psoriasiform dermatitis when present as the predominant microscopic features.
On RCM, spongiosis is detectable as dark areas involving the level of the epidermis in comparison with the darker surrounding epithelium appears with broadband intercellular spaces. Dark areas are associated with the presence of round-to-polygonal, mildly refractive cells corresponding on histopathology with inflammatory cells located between keratinocytes in the epidermis ( Fig. 1 ). Notably, spongiosis, when mild to moderate, can be also detected in the other major groups of inflammatory skin diseases as sign of epidermal infiltration of inflammatory cells.
As mentioned, in spongiotic dermatitis semiquantitative estimation of the severity of the spongiosis that is generally detected at least moderate and more commonly severe until massive, has to be considered as more indicative for an acute spongiotic dermatitis. When the spongiosis is severe, it shows up as intraepidermal vesicle seen on RCM as round to polylobular, well-defined, deeply dark spaces delineated by keratinocytes pushed to the periphery of the area without an epithelial wall. The round intraepidermal area is filled by bright, round inflammatory cells in the context of a dark background corresponding with inflammatory cells (see Fig. 1 ). When fast developed (commonly detectable in irritant contact dermatitis), spongiosis appears as a large dark area with “intravesicular” septa clinically corresponding with fast developing blisters.
In spongiotic dermatitis, RCM of the superficial epidermal layers can reveal disrupted stratum corneum associated with detached corneocytes. Individual corneocytes may appear as floating, highly refractile polygonal cells that correspond to subtle desquamation, and reflecting the loss of cohesiveness of corneocytes in response to contact irritants agents.
The dermoepidermal junction (DEJ) is typically preserved with well visible and bright papillary rims. In the upper dermis, in real-time imaging, dilated vessels are generally detectable as round to canalicular structures filled by a prevalence of moving, mildly bright, not nucleated cellular structures (erythrocytes) and a minority of brighter cellular elements (leukocytes). Inflammatory cells are also detectable around dilated vessels.
Differentiation between irritant contact dermatitis and allergic contact dermatitis has been described to be possible through the evaluation of the changes involving the stratum corneum during time. In detail, irritant contact dermatitis reaction typically shows a pronounced superficial disruption of the stratum corneum after the exposure to contact irritants (<24 hours); this dynamic evolution of the stratum corneum involvement is generally absent in allergic contact dermatitis. Dilated vessels and dermal inflammation can be visualized as secondary confocal features in both the subtype of spongiotic dermatitis. It has been shown that irritant and allergic contact dermatitis differ in term of kinetic evolution; irritant contact dermatitis reactions have a more rapid onset and shows a faster recovery compared with allergic contact dermatitis. In addition, it was demonstrated that RCM allows in the detection of subclinical reaction to in experimental application of antigens when clinical features are absent or subtle, thereby verifying clinical readings of patch test (Ardigo, unpublished data, 2009).
Psoriasiform dermatitis
The prototypic entities of this group are plaque psoriasis (PP) and seborrheic dermatitis. Reports on therapeutic follow-up of PP using RCM during topical and systemic treatment have been also reported in literature, demonstrating the possibility of detailed monitoring of microscopic changes during treatment and actives efficacy noninvasive evaluation at a microscopic level.
Psoriasiform dermatitis, also named hyperkeratotic disease, is characterized by thickened stratum corneum and epidermis associated with papillomatosis (elongation of the rete ridges). The thickening of the stratum corneum can be evaluated using Viva Stack software analysis calculating the number of single steps needed to move above the stratum corneum (where the plastic window is seen as a bright round circle) and progressing deeper in 5-μm steps to the first cellulated epidermal layer; the stratum corneum is considered thickened when the total thickness is greater than 20 μm on the face or 40 μm on the other location. Moreover, at the level of the stratum corneum, the presence of high refractive round to polygonal structures corresponds to parakeratosis typical for PP at histology. The thickness of the epidermis can be also calculated using Stack acquisition starting from the first cellulated layer up to the first appearance of papillary dermis, progressing through stack images of 5-μm steps. The epidermis is “thickened” when the minimum keratinocytes layer thickness is greater than 60 μm on the face or 90 μm on the other body sites.
Other RCM criteria commonly detected and generally indicative for PP are the presence of uplocated, enlarged dermal papillae (DP) and nonrimmed DP at the spinous layer with thin interpapillary epidermal spaces ( Fig. 2 ). In detail, the papillae are increased in number and density at the level of the spinous layer as well as at the DEJ compared with normal skin and according to the anatomic site. This is considered an indirect feature of papillomatosis viewed from the horizontal approach to the skin of RCM. The confocal features characterizing papillomatosis are generally seen diffusely involving the erythematous lesion in PP and only focal in seborrheic dermatitis.
