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INTRODUCTION TO CHAPTER

Psoriasis, seborrheic dermatitis, pityriasis rosea, and lichen planus are diseases that present with papulosquamous lesions (scaly papules and plaques). Although these diseases may have a similar morphology, their underlying etiologies vary. Secondary syphilis, cutaneous T cell lymphomas, and connective tissue disease may also present with papulosquamous lesions and should be included in the differential diagnosis.

PSORIASIS

Introduction

Key points for psoriasis

  • ✓ Psoriasis is a common, chronic inflammatory disease that typically presents with scaly red to salmon pink plaques on the elbows, knees, scalp, lower back, and gluteal cleft.

  • ✓ About 1/3 of patients with psoriasis will develop psoriatic arthritis during their lifetime.

  • ✓ Cardiometabolic disease, gastrointestinal diseases, kidney disease, and mood disorders are common comorbidities in patients with psoriasis.

  • ✓ Most patients with mild to moderate psoriasis can be managed with topical medications and/or phototherapy.

Psoriasis is a common, chronic, inflammatory, immune-mediated disease. Clinicians and patients have long been vexed by this ancient affliction. Although most medical literature prior to Willan (1757–1812) lumped psoriasis, leprosy, eczema, and other inflammatory dermatoses into a confusing menagerie, Celsus gave a convincing account of psoriasis vulgaris almost 2,000 years ago. His description included many of the morphologic features that physicians today utilize to diagnose psoriasis, including: the "ruddy" or salmon-colored plaques with silvery scales that often are associated with punctate hemorrhage or "erosions" when removed.1

More than 7.5 million adults (2.1% of the population) in the United States are affected and 30% of these individuals will develop psoriatic arthritis.2 About 1.5 million patients are considered to have moderate to severe disease.

Psoriasis may have a significant negative impact on the patient's quality of life. Patients often are self-conscious, depressed, or frustrated over the appearance of their skin. Studies have found that between 5 and 10% of psoriasis patients suffer from depression, anxiety, and other mental health comorbidities.3

Psoriasis spans all socio-economic groups, and its prevalence varies by geographic location. Historically, the disease is more common in the northern latitudes. The rate of psoriatic disease is lower in African-Americans compared to European-Americans.2

Pathogenesis

The primary cause of psoriasis is dysregulation of the cell mediated, adaptive immune response, but a genetic predisposition along with environmental triggers are also postulated to play a role. A positive family history for psoriasis can be found in 35% of patients4 and HLA-Cw6 is a well-researched gene implicated in psoriasis.

The dysregulation seen in psoriasis is likely triggered by hyperactivity of the innate immunological surveillance system to environmental antigens. In genetically predisposed individuals, the Th1 pathway response is over-stimulated and this overproduction of Th1 related cytokines along with interleukin -12, 17, and 23 causes hyper-proliferation of epidermal keratinocytes. These events lead to the formation of ...

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