What is Psoriasis
Psoriasis is a chronic, genetic, systemic inflammatory disease characterized by well-demarcated, erythematous (red) plaques with silvery scale, most commonly affecting the scalp, elbows, knees, and presacral region. 1
Core Disease Characteristics
Psoriasis is fundamentally a multisystem inflammatory disorder that extends beyond the skin, affecting approximately 2% of the population worldwide. 1 The disease results from inappropriate activation of cutaneous T cells and dendritic cells with subsequent release of inflammatory cytokines and mediators. 1
Pathophysiology
Accelerated keratinocyte turnover is the hallmark cellular abnormality, with the epidermal cell reproduction cycle shortened from the normal 28 days to approximately 4 days, resulting in immature cell deposition and characteristic scaling. 2
Immune dysregulation involves complex interplay between Th1/Th2 homeostasis, the Th17/Treg balance, and the IL-23/Th17 axis, with Th17 cells playing a particularly critical role in creating an integrated inflammatory loop with dendritic cells and keratinocytes. 3
Genetic predisposition is significant, with susceptibility linked to HLA-Cw6 (PSORS1), though environmental factors can alter disease expression. 1, 4
Clinical Presentation
Classic Plaque Psoriasis (Psoriasis Vulgaris)
Well-demarcated plaques with thick silvery scale on an erythematous base are the defining features. 1
Common locations include scalp, extensor surfaces (elbows, knees), presacral region, though any skin area may be involved including palms, soles, nails, and genitalia. 1
Pruritus and pain are frequent symptoms that significantly impact quality of life. 1
Other Clinical Variants
Guttate psoriasis presents as dew-drop-like, 1-10 mm salmon-pink papules with fine scale, primarily on trunk and proximal extremities, most common in individuals under 30 years. 1
Inverse psoriasis affects skin folds (axillary, genital, perineal, intergluteal, inframammary areas) with erythematous plaques and minimal scale due to moisture. 1
Pustular psoriasis shows clinically apparent collections of neutrophils, ranging from localized palmoplantar involvement to generalized von Zumbusch variant with fever and systemic toxicity. 1
Erythrodermic psoriasis involves generalized erythema covering nearly the entire body surface with varying degrees of scaling, potentially causing thermoregulatory dysfunction, hypothermia, and dehydration. 1
Disease Severity Classification
Severity is defined by body surface area (BSA) involvement: less than 3% BSA is mild, 3-10% BSA is moderate, and greater than 10% BSA is severe disease. 1
Critical caveat: Psoriasis can be severe irrespective of BSA when it causes serious emotional consequences, occurs in high-impact locations (hands, feet, scalp, face, genitals), or causes intractable pruritus. 1
Systemic Associations and Comorbidities
Psoriatic arthritis develops in 30-33% of adult patients with psoriasis, making it a member of the seronegative spondyloarthropathies. 1, 4
Cardiovascular and metabolic complications are significantly increased, including:
- Diabetes and metabolic syndrome components 1, 4
- Cardiovascular disease and coronary artery disease 1, 4
- Nonalcoholic fatty liver disease 1
Other immune-mediated associations include inflammatory bowel disease (Crohn's disease 3.8-7.5 times more frequent), lymphoma, and multiple sclerosis. 1, 4
Disease Course
Psoriasis is a chronic, lifelong condition that waxes and wanes throughout the patient's lifetime, is modified by treatment initiation and cessation, and has few spontaneous remissions. 1 The visible and disfiguring nature of the disease ensures significant physical and psychosocial effects on patients. 1, 2