A plaque is an elevated lesion that occupies a much larger surface area than a papule. It may be a confluence of papules or have the same pathologic features of a papule, but spread out over a larger surface. Plaques may be primarily composed of dermal elements, e.g. metabolic deposits, granulomatous inflammation, or neoplasms; primarily composed of epidermal components, e.g. hyperplastic epidermis induced by chronic scratching or rubbing (lichenification); or both. In this drawing, epidermal hyperplasia with roughening of the skin surface is shown. Generally, plaques with well-circumscribed margins have a greater epidermal component, and those wit h poorly circumscribed margins have a greater dermal component.
This illustration shows both papules (the small reddish scaly lesions), and plaques, formed by the confluence of papules. The silvery, reflective quality of the scales taken together with the distribution of lesions on the extensor surface of the elbow is diagnostic for psoriasis.