What clinical sign suggests the presence of psoriasis during a skin examination?

The presence of psoriasis is often indicated by the Auspitz sign during a skin examination. This sign is characterized by pinpoint bleeding that occurs when psoriatic plaques are scratched or removed. The bleeding is due to the deranged capillary loops in the dermal papillae that are located just beneath the surface of the skin, which become exposed when the thickened, silvery scales of the plaques are lifted. This clinical observation is quite specific to psoriasis and helps differentiate it from other skin conditions.

Köbner phenomenon, while associated with psoriasis, is a broader term that refers to the development of new psoriatic lesions in response to skin trauma. Darier's sign, on the other hand, is used in the context of mast cell disorders, such as urticaria pigmentosa, where scratching the skin elicits a wheal. Lichenification refers to thickened, leathery skin resulting from chronic scratching or rubbing and is not exclusive to psoriasis. Therefore, the Auspitz sign is the distinctive clinical indicator that points specifically to the diagnosis of psoriasis.