Plaque Psoriasis Overview and Epidemiology

Plaque Psoriasis (Psoriasis Vulgaris)

Chronic, multifactorial, non-contagious, inflammatory, hyperproliferative epidermal disease.
Characterized by recurrent, well-demarcated, thickened, erythematous scaling plaques with silvery white scales.
Results from increased epidermal cell turnover rate.
Although rarely life-threatening, the clinical appearance can be cosmetically disfiguring and physically/emotionally debilitating.
Prevalence in adults ranges from 1 to 8.5%, and in children from 0 to 2%.
No clear gender predilection, but may occur slightly more in females than males. Less common in tropics and dark-skinned individuals.
Bimodal peak of age of onset: greatest incidence between 30 and 39 years, and a smaller peak between 50 and 69 years. Can present at any age, including pediatric age group.

Epidemiology

Prevalence in adults ranges from 1 to 8.5% and in children from 0 to 2%.
No clear gender preference, but may slightly more common in females.
Less common in tropical and darkly pigmented populations.
Bimodal peak of age for onset: highest incidence between 30 - 39 years old, with a secondary peak between 50 - 69 years.
Psoriasis can be seen at any age.

Genetic Factors

Psoriasis is complex and multifactorial.
Associated with interaction between environmental and specific genetic/immunologic backgrounds.
Significant genetic component (around 40% of patients have at least one first-degree relative with the disorder).
Multiple genetic loci identified (PSORS 1-9).
PSORS1 on chromosome 6 is the strongest susceptibility locus (accounts for one-third to one-half of the genetic liability).
Additional genes affecting T helper cell functions (IL-12 and IL-23) play a role.

Triggering Factors

Physical or chemical injury to skin (cuts, burns)
Infections (streptococci, staphylococci, viral, respiratory tract).
Medications (beta-blockers, lithium, antimalarials, hydroxychloroquine, NSAIDs, aspirin, tetracycline, steroids)
Psychological stress
Environmental factors (cold)
Endocrine and hormonal changes (menopause)
Overweight, obesity, unbalanced diet
Tobacco and alcohol consumption.
Sun exposure and hot weather often improve lesions.

Pathophysiology

Overactive T cells migrate to the epidermis, triggering immune responses, attacking healthy skin cells as if to heal a wound or fight infection.
Blood vessel dilation in skin around plaques.
Production of various cytokines (TNF-α, IL-2, IL-8, IL-10, and INF-γ).
Increased production of skin cells and other white blood cells.
Scaling and erythema result from hyperproliferation and abnormal differentiation of the epidermis, as well as inflammatory cell infiltrates and vascular dilation.
Increased cell numbers undergoing DNA synthesis.
Shortened cell cycle time for keratinocytes.
Decreased epidermal turnover time (4 days vs. 28 days in normal skin).
Abnormal differentiation.
Dead skin cells and white blood cells don't slough off quickly enough, accumulating into thick, scaly patches.

Histopathology

Surface "silver" scale.
Erythematous base.
Persistence of nuclei in stratum corneum (parakeratosis).
Microabscesses.
Dilation and tortuosity of papillary vessels.
Edema and inflammation of dermis.

Clinical Manifestations

Chronic and relapsing course with exacerbations and remissions.
Lesions begin as small papules that grow and coalesce into plaques, ranging from less than 1-10 cm in diameter.
Well-circumscribed, sharply demarcated, light pink to bright red in color, usually symmetrical distribution.
Characteristic thick, opaque, silvery scale that can be peeled off in layers.
Recent bathing and moisturizers may temporarily disguise lesions.
Minimal itching (occurs in only 25% of patients).
Skin becomes either hypopigmented or hyperpigmented after lesions resolve.

Common Sites of Involvement

Most common: scalp, lumbar regions of back, external ear, extensor surfaces of elbow and knee.
Nail involvement: pitting, onycholysis, affects 50% of fingernails, and 35% of toenails.
Psoriatic arthritis affects 7% of patients, involving joints often asymmetrically, causing disability and deformity.

Topical Therapy

First line for mild to moderate disease.
Corticosteroids: cornerstone; well-tolerated and effective, anti-inflammatory, antiproliferative, immunosuppressive, vasoconstrictive. Dosage: 1-2 times daily (can be combined with other topical agents, UV light, and systemic agents. Duration: class 1 (highest potency) 2-4 weeks of treatment. Less potent agents, endpoint unknown. Common examples: betamethasone, hydrocortisone, mometasone, clobetasole.
Calcineurin Inhibitors: Tacrolimus and pimecrolimus. Often used for thinner skin (e.g., face). Long-term use (>4 weeks). Side effects: burning, itching, flushing with alcohol. Long-term intermittent use can increase lymphoma risk.
Vitamin D Analogues (Calcipotriene): Synthetic Vitamin D3 analogue affecting cellular differentiation/proliferation and regulating apoptosis. Effective in treating mild-moderate psoriasis and sometimes combined for greater effect. Available as lotions/ creams. Side effects: itching, burning, redness, dryness, edema, irritation.
Tazarotene: Topical Vitamin A derivative useful in combination with topical corticosteroids, affecting cellular proliferation and differentiation. Helpful in palmar-plantar and nail psoriasis. Side effects: irritation, dryness, and burning.
Salicylic Acid: Keratolytic, used for thick plaque psoriasis. Removes scales, allowing topical corticosteroids to penetrate better. Also effective for treating mild-moderate psoriasis, especially on thick plaques. Side effects: irritation.
Anthralin: Antiproliferative, inhibits DNA synthesis. Can stain skin and clothing. Not first or second choice due to staining and irritation issues. Usually to be used overnight and washed off in morning. Topical dose can last 8-12 weeks.
Coal Tar: Used in shampoos and creams. Epidermal thinning, no fully understood mechanism. Effective for treating mild-moderate psoriasis.

Other Treatments

Phototherapy: UV light use to inactivate immune cells and lessen inflammation/epidermal cell turnover. Effective with varied forms of U.V radiation. 3-times-a-week is recommended.
Systemic Therapy: Methotrexate, cyclosporine, acitretin, apremilast used for moderate-severe psoriasis.
Biologic Agents: Anti-TNF agents, monoclonal antibodies (ustekinumab, secukinumab, ixekizumab, brodalumab, guselkumab, tildrakizumab, risankizumab). Used for severe, unresponsive psoriasis.
Combinations: Topical calcipotriene + standard dose methotrexate, Calcipotriene/betamethasone + low dose cyclosporine, Calcipotriene + standard dose acitretin.

New FDA-Approved Products

**Roflumilast:**PDE-4 inhibitor, topical use for mild-severe plaque psoriasis (including intertriginous areas).
Tapinarof: aryl hydrocarbon receptor modulator, topical use for mild-severe plaque psoriasis (including intertriginous areas).

Important Considerations

Side Effects: Common (and serious) side effects are mentioned regarding specific medication classes throughout the document.
Pregnancy Category and other Contraindications: Critical information regarding these factors are listed throughout the document.