Psoriasis vulgaris is a common chronic inflammation skin disorder that affects approximately 1.5% to 2% of the population.
The term psoriasis is derived from the Greek word psora that means itch.
Psoriasis vulgaris is also referred to plaque psoriasis because of the characteristic plaque formation on the skin. The well-defined patches of red raised skin, usually involves the knees, elbows, scalp, trunk and nails. The flaky silvery white buildup composed of dead skin cells on top of the plaques is called scale. Affected skin is generally very dry, with possible superimposed symptoms of aching, itching, and cracking.
The pathogenesis of psoriasis is not fully understood. There are two main hypotheses regarding development of the disease. The first considers psoriasis primarily as a disorder of excessive growth and reproduction of skin cells. The second hypothesis believes that psoriasis is an immune- mediated disorder. It is thought that T cells become active, migrate to the dermis and trigger the release of certain cytokines especially tumor necrosis factor-alpha (TNF?), which causes inflammation and the rapid production of skin cells . However, it is not known what initiates the activation of the T cells.
The histologic appearance varies considerably with the stage and severity of the disease.
At the early stage, there are non- specific signs such as capillary dilation and edema in the papillary dermis with pericapillary lymphocyte infiltration. The diagnostic feature in this stage is the so-called Munro microabscesses, the infiltration of neutrophils into the area of parakeratosis. If there is excessive exocytosis of neutrophils, they may aggregate to form small spongioform pustules of Kogoj.
The fully developed lesions are characterized by acanthosis with rete ridge elongation, thinning of the suprapapillary epidermis with small spongiform pustules, diminished granular layer, confluent parakeratosis, presence of Munro microabscesses, dermal papillary edema, and dilated capillaries. Of all these listed features, only the spongiform pustules of Kogoj and Munro microabscesses are truly diagnostic.
REF: Chen M, Bruno E, Santos EE, Sarma DP (2007). A brief review of the “vulgaris” lesions of the skin. The Internet J Dermatol 6(1).
Deba P Sarma, MD., Omaha