Diascopy is very helpful in the diagnosis of –

Diascopy is of particular value in detecting granulomatous nodules, which have a translucent brownish colour known as 'apple jelly' nodules, e.g. in lupus vulgaris. In Naevus anaemic, localized vasoconstriction, other pigments are unaltered - diascopy of adjacent skin, therefore, reveals an identical colour to that of the depigmented area. By contrast, diascopy of skin adjacent to vitiligo, in which there is a loss of melanin, demonstrates that the vitiligo remains paler. Application of medium pressure to a spider naevus can compress radiating arterioles and allow visualization of pulsatile flow in the feeding vessel. Palpable purpuric lesions that do not blanch on pressure (diascopy) suggest vasculitis.