Diascopy

Diascopy (from Greek dia – through and skopeo – looking) is a simple but important diagnostic method in dermatology, which consists of pressing on the rash element with a transparent object (slide, glass spatula or transparent ruler).

The procedure allows you to de-blood the skin at the site of pressure by displacing blood from the vessels of the microcirculatory bed.

Clinical significance

The method is used for differential diagnosis of stains:

• Vascular (inflammatory) spots: Pale or disappear when pressure is applied as blood escapes from the dilated vessels. When pressure is stopped, the color is restored.
• Hemorrhagic spots (petechiae, purpura): Do not change color when pressed because the red blood cells are outside the vascular bed (have saturated the tissue) and cannot be “squeezed out”.

Diascopy is also used in the diagnosis of tuberculous lupus erythematosus (the symptom of “apple jelly” – when pressing the nodules acquire a yellowish-brown color).