Pathogenesis and diagnosis of contact dermatitis: Applications of reflectance confocal microscopy

Table 1 Pathophysiologic features of allergic contact dermatitis and irritant contact dermatitis

	ICD	ACD
Blood immunology	No specific T cells	Presence of specific T cells
Skin immunology	No activated T cells	Presence of activated T cells
Innate immune system	+++β	+ (it due to the maduration of skin DC)
Adaptative immunity	-	+++ (delayed-type hypersensitivity response)
Cytokines and chemokines	IL-1α and β, IL-6, IL-8, TNF-α, GM-CSF and IL-10	IL-23, IL-36Ra, IL-2 and IL 17

+++: Strong positive association; +: positive association; –: negative association. ACD: Allergic contact dermatitis; ICD: Irritant contact dermatitis; TNF:Tumor necrosis factor; IL: Interleukin; DC: Dendritic cells.

Table 2 Diagnostic features to differentiate irritant contact dermatitis and allergic contact dermatitis with reflectance confocal microscopy

	ICD	ACD
Stratum corneum	Parakeratosis: +++ (early stage) Corneocyte detachment: +++ (early stage)	-
Stratum granulosum and spinosum (1st wk)	Exocytosis: +++ Spongiosis: +++ Necrosis: +++ Vesicles: +++	Exocytosis: + Spongiosis: + Necrosis: + Vesicles: ++
Stratum granulosum and spinosum (2nd wk)	Exocytosis: +++ Spongiosis: +++ Necrosis: +++ Vesicles: +++	Exocytosis: ++++ Spongiosis: +++ Necrosis: +++ Vesicles: +++
Superficial perivascular infiltrate	+	+
Capillary dilation in the dermal papillae and leukocyte traffic	+	+

+++: Strong positive association; ++: Moderate positive association; +: Positive association; –: Negative association. ACD: Allergic contact dermatitis; ICD: Irritant contact dermatitis.