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The primary lesions in this reaction pattern are scaly papules, plaques and nodules. A myriad of diseases display this reaction pattern. As mentioned in Chapter 5, some blistering diseases may have a papulosquamous presentation, such as pemphigus foliaceus, and some diseases that primarily have dermal inflammatory infiltrates or cells histopathologically may also be scaly, such as granular cell tumors, deep fungal infections, and plaques and nodules seen in halogenoderma.
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Clinical Tip
Any primary lesion that is raised and scaly, no matter how it is formed, may be characterized as a papulosquamous lesion.
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There is significant overlap between the papulosquamous and eczematous reaction patterns, as some forms of eczema fulfill the papulosquamous definition above. Examples include seborrheic dermatitis and lichen simplex chronicus. These diseases can fit into either reaction pattern.
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Clinical Tip
Papulosquamous and eczematous reaction.patterns overlap; eczematous conditions such as seborrheic dermatitis and lichen simplex chronicus also fit into the papulosquamous reaction pattern.
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Sometimes the scales of papulosquamous diseases are not conspicuous, in which case plaques can seem to fit into the dermal reaction pattern. An example here is any scaly dermatosis in an intertriginous area, where maceration of scales occurs. Another such example is the inflamed variant of seborrheic dermatitis that occurs on the face. Here, pink plaques have little scale and these plaques could be intuited as being dermal.
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Clinical Tip
The papulosquamous reaction pattern may masquerade as dermal reaction pattern, when scales are not conspicuous.
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The list of papulosquamous diseases is lengthy. As discussed in the introduction, it is useful to make one’s own lists of diseases by diagnostic determinants, reaction pattern, grouping, configuration, and distribution when learning about each disease. It is also useful when encountering a patient with a papulosquamous disorder to have a ready-made differential diagnostic list that can be applied to the presenting dermatosis. Table 6.1 contains such a list, which is comprehensive, but by no means complete. This list is subdivided into more digestible categories using the etiologic classification and a short description of these dermatoses follows here, including their morphologic features. Images of many of these conditions have been grouped together on the basis of morphologic grounds as outlined later in the chapter.
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