Psoriasis

What it is

Psoriasis is a common chronic skin disorder, with a prevalence around 2%. It is recurrent, and is characterized by well-circumscribed erythematous papules and plaques with silvery-white scales. Another page gives it as a chronic immune-mediated skin disease with predominantly skin and joint involvement, a strong genetic predisposition, and a course that waxes and wanes during the patient's lifetime.

The way the lesion is described in practice is worth holding: the primary lesion is plaques and the secondary lesions are scales; the color erythematous or pink, the shape round, the border well-demarcated, the size 1-5 cm, and the distribution bilateral over the knees. Put together, that reads as several 1-5 cm sized erythematous well demarcated plaques with white scales bilaterally distributed over the extensor surface of the knees.

Causes and risk

The pathophysiology is multifactorial and not yet fully understood:

• Genetic: associated with HLA-B13, -B17 and -Cw6, with strong concordance, 70%, in identical twins
• Immunological: abnormal T cell Th17
• Environmental: worsened by skin trauma and stress, triggered by streptococcal infection, improved by sunlight