DR3.2 | Grattage Test Technique — Summary & Reflection

KEY TAKEAWAYS

The Grattage test (Brocq's method) is a quick, low-cost bedside procedure that supports the diagnosis of psoriasis by graded scraping of a plaque to elicit three sequential endpoints: the candle-grease sign (silvery parakeratotic scale flaking off), the glistening last membrane (terminal film / Büchner sign), and the Auspitz sign (pinpoint bleeding from exposed dilated dermal papillary capillaries). Each sign is a direct consequence of psoriatic architecture — loose parakeratotic scale over a thinned suprapapillary epidermis with dilated capillaries — so the test must use a blunt instrument and gentle, graded pressure; a sharp blade produces misleading traumatic bleeding. A full positive sequence supports psoriasis; greasy scale with no membrane or bleeding (seborrhoeic dermatitis) and violaceous papules without Auspitz (lichen planus) are negative. The test is contraindicated on inflamed, pustular, erythrodermic, infected, or anticoagulated skin. Performed and interpreted correctly, it is a reliable, safe diagnostic aid; performed carelessly it misleads or harms.

REFLECT

Imagine you are in a rural posting with a long OPD queue, no biopsy facility, and a patient whose scaly plaque could be psoriasis or seborrhoeic dermatitis. How confident would you feel performing the Grattage test on the spot, and what would you watch for at each layer? Reflect on the discipline the test demands — choosing a blunt instrument, scraping gently and in sequence, and pausing to observe rather than digging for a result. Consider, too, how you would explain to the patient what you are doing and why, and how you would avoid the temptation to over-interpret a single sign. What will you practise — on models, on willing patients under supervision — so that this becomes a smooth, safe, and reliable part of your bedside repertoire?