What is Psoriasis
Psoriasis is a chronic, genetic, systemic inflammatory disease characterized by well-demarcated, erythematous plaques with silvery scales that result from accelerated skin cell turnover driven by immune system dysfunction. 1, 2
Core Disease Characteristics
Psoriasis is fundamentally an immune-mediated disorder where the body's immune system mistakenly attacks healthy skin cells, causing them to proliferate at an abnormally rapid rate. 1, 3 This accelerated cell cycle creates the characteristic scaly, erythematous patches, papules, and plaques that are often severely pruritic (itchy) or painful. 1
The disease affects approximately 2-3% of the population worldwide, with significant variation across different regions. 1, 3 It is not contagious and cannot spread through air, water, or physical contact. 4
Clinical Presentation
The classic presentation includes:
- Well-defined erythematous plaques with thick silver scales 2, 5
- Common locations: scalp, elbows, knees, and presacral region 2, 6
- Additional sites may include palms, soles, nails, genitalia, and intertriginous areas 6
- Lesions are typically symmetrically distributed 1
The plaques are characterized by three key features: erythema (redness), induration (thickening), and scaling. 6
Clinical Variants
Psoriasis presents in multiple distinct forms:
Plaque Psoriasis (Most Common)
The predominant form, accounting for the majority of cases, with chronic, stable, raised plaques covered by silvery scales. 1, 4
Guttate Psoriasis
Characterized by small (1-10 mm), salmon-pink, dew-drop-like papules with fine scale, primarily on the trunk and proximal extremities. 1 This variant is common in individuals younger than 30 years and often follows streptococcal pharyngitis or upper respiratory infections. 1, 6
Inverse Psoriasis
Affects skin folds (axillary, genital, perineal, intergluteal, inframammary areas) with erythematous plaques and minimal scale due to moisture in these regions. 1
Pustular Psoriasis
Features clinically apparent collections of neutrophils forming pustules, either generalized (von Zumbusch variant with fever and toxicity) or localized to palms and soles. 1
Erythrodermic Psoriasis
A severe form with generalized erythema covering nearly the entire body surface area with varying degrees of scaling, potentially causing hypothermia, dehydration, fever, and malaise. 1
Systemic Nature and Comorbidities
Psoriasis is a multisystem disease, not merely a skin condition. 1 It is strongly associated with:
- Psoriatic arthritis (affects 25-30% of psoriasis patients) with joint pain, swelling, morning stiffness, enthesitis, and dactylitis ("sausage digits") 6, 7
- Metabolic syndrome components: diabetes, hypertension, dyslipidemia, obesity 6, 5, 3
- Cardiovascular disease: increased risk of coronary artery disease, myocardial infarction, and stroke 1, 6, 5
- Inflammatory bowel disease: Crohn's disease (3.8-7.5 times more frequent) and ulcerative colitis 5, 3
- Mental health conditions: depression and significant psychosocial impact 7, 3
- Other conditions: nonalcoholic fatty liver disease, lymphoma, nonmelanoma skin cancers 7, 3
Pathophysiology
The disease results from an interaction between genetic susceptibility (particularly HLA-Cw6/PSORS1 gene) and environmental triggers. 5, 8 The immune system dysfunction involves specific cytokines, particularly TNF-alpha, IL-17, and IL-23, which drive the inflammatory cascade. 8
Disease Course
Psoriasis is a chronic, lifelong condition that waxes and wanes, with few spontaneous remissions. 1 The disease severity and activity fluctuate over time, often modified by treatment initiation and cessation. 1
Triggering and Exacerbating Factors
Common triggers include:
- Infections: streptococcal pharyngitis, perianal infections, upper respiratory infections 6
- Medications: beta-blockers, lithium, antimalarials, NSAIDs, tetracyclines 6
- Lifestyle factors: smoking, tobacco consumption, excess alcohol 6, 3, 4
- Stress and trauma 8
Quality of Life Impact
The disease causes significant disfigurement and can lead to social withdrawal, avoidance of activities, shame, bullying, and impact on relationships. 1, 6 The visible nature of lesions, combined with pruritus and pain, substantially affects patients' daily functioning and psychological well-being. 1