Blanching versus non-blanching lesions and diascopy

What it is

Blanching or nonblanching is one of the points noted when describing a skin lesion. A blanching lesion disappears or turns white under pressure; a non-blanching lesion does not.

Causes and risk

Henoch-Schonlein purpura is a small vessel vasculitis whose key feature is purpura, a non-blanching rash, together with IgA nephritis and glomerulonephritis; the wider picture is palpable purpura, arthralgia, abdominal pain and renal involvement, and the classic exam clue is a child with purpura on the legs, abdominal pain and hematuria after a URI.

Purpura appears in other forms of vasculitis as well. Palpable purpura is listed among the features of cryoglobulinemic vasculitis, skin purpura among the features of Churg-Strauss, and the cutaneous manifestations of Wegener's granulomatosis are palpable purpura and ulcerations.