Psoriasis Clinical Overview: Signs, Diagnosis, & Classification

What is psoriasis?

Psoriasis is a chronic inflammatory skin condition characterised by clearly defined, red and scaly plaques. It is classified into several types.

Well demarcated plaques with silvery scale in chronic plaque psoriasis

Scalp psoriasis often extends beyond the hair line

What are the clinical features of psoriasis?

Psoriasis usually presents with symmetrically distributed, red, scaly plaques with well-defined edges. The scale is typically silvery white, except in skin folds where the plaques often appear shiny with a moist peeling surface. The most common sites are the scalp, elbows, and knees, but any part of the skin can be involved. The plaques are usually very persistent without treatment.

Itch is mostly mild but may be severe in some patients. Itch leads to scratching and lichenification characterised by thickened leathery skin and increased skin markings. Painful skin cracks or fissures may occur, particularly on the palms and soles.

Psoriasis can demonstrate the Koebner phenomenon. This involves the generation of new psoriatic lesions on the skin that has previously been damaged or irritated (injury, burns etc.)

When psoriatic plaques clear up, they may leave brown or pale marks (postinflammatory hypo- or hyperpigmentation) that can be expected to fade over several months.