Chapter 136: Psoriasis

Patient Story

A 5-year-old boy presents to his pediatrician with a new onset rash 2 weeks after being treated for strep pharyngitis. He had been treated with a10-day course of amoxicillin after a positive rapid strep test in the office. The mother states that her son is otherwise feeling well with a good appetite and no change in his activities. The pediatrician notes small plaques on the child’s face, arms and trunk and sees the resemblance to drops of water (Figure 136-1). The vital signs are normal as is the rest of the physical examination. A diagnosis of guttate psoriasis is made without any laboratory tests or biopsies. The child is started on 0.1 percent triamcinolone ointment to be applied twice daily. A referral to dermatology is also made.

Introduction

Psoriasis is a chronic inflammatory papulosquamous and immune-mediated skin disorder. It is also associated with joint and cardiovascular comorbidities. Psoriasis can present in many different patterns, from the scalp to the feet, and cause psychiatric distress and physical disabilities. It is crucial to be able to identify psoriasis in all its myriad presentations so that patients receive the best possible treatments to improve their quality of life and avoid comorbidities.

Epidemiology

• Psoriasis affects approximately 2 percent of the world population.¹

• The prevalence of psoriasis was 2.5 percent in white patients and was 1.3 percent in African American patients in one population study in the US.²

• Sex—No gender preference.

• Age—Psoriasis can begin at any age. In one population study of the age of onset of psoriasis two peaks was revealed, one occurring at the age of 16 years (female) or 22 years (males) and a second peak at the age of 60 years (female) or 57 years (males).³

• The prevalence rates for pediatric psoriasis increased in a linear way from 0.2 percent at the age of one year to 1.2 percent at the age of 18 years in a German study.⁴

• Psoriasis begins before the age of 20 in about 1/3 of patients.⁵

• Psoriatic arthritis affects about 20 percent of all psoriasis patients.⁵

Etiology and Pathophysiology

• Immune-mediated skin disease, where the T cell plays a pivotal role in the pathogenesis of the disease.

• Langerhans cell (antigen-presenting cells in the skin) migrate from the skin to regional lymph nodes, where they activate T cells that migrate to the skin and release cytokines.

• Cytokines are responsible for epidermal and vascular hyperproliferation and proinflammatory effects.