Introduction
Key features
Psoriasis is a chronic, immune-mediated disorder that results from a polygenic predisposition combined with environmental triggers, e.g. trauma, infections, medications, psychological stress
The underlying pathophysiology involves various classes of T cells and their interactions with dendritic cells and cells involved in innate immunity, including neutrophils and keratinocytes
Identification of susceptibility genes has pointed to a major role for the innate and adaptive immune systems as well as altered epidermal differentiation
Sharply demarcated, scaly, erythematous plaques characterize the most common form of psoriasis; occasionally, sterile pustules are seen
The most common sites of involvement are the scalp, elbows, and knees, followed by the nails, hands, feet, and trunk (including the intergluteal fold)
Typical histologic findings include acanthosis with elongated rete ridges, hypogranulosis, hyper- and parakeratosis, dilated blood vessels, and a perivascular infiltrate of lymphocytes with neutrophils singly or within aggregates in the epidermis
Psoriatic arthritis is the major associated systemic manifestation and the most common presentation is asymmetric oligoarthritis of the small joints of the hands and feet; other comorbidities include depression, metabolic syndrome, and cardiovascular disease in patients with moderate to severe disease
Topical therapy is used to treat limited disease, whereas photo- therapy, methotrexate, cyclosporine, and targeted immunomodulators (“biologic” therapies) that modify key immune effector cells and cytokines lead to significant clinical improvement of moderate to severe psoriasis