Psoriasis

Chronic immune-mediated inflammatory skin condition driven by T-cell (Th17) activation, causing keratinocyte hyperproliferation.

Genetic predisposition with environmental triggers (streptococcal infection, trauma/Koebner phenomenon, stress, alcohol, smoking, certain drugs: lithium, beta-blockers, antimalarials, abrupt steroid withdrawal).

Classified: plaque psoriasis (most common, ~80-90%), guttate (post-streptococcal, small droplet lesions, often children/young adults), flexural/inverse (skin folds, minimal scale), pustular (localized or generalized: von Zumbusch, can be life-threatening), erythrodermic (>90% BSA, systemic illness risk: emergency).

Well-demarcated, erythematous plaques with silvery scale, symmetric distribution: extensor surfaces (elbows, knees), scalp, lower back classically.

Nail changes: pitting, onycholysis, oil-drop sign, subungual hyperkeratosis. Auspitz sign: pinpoint bleeding on scale removal. Koebner phenomenon: lesions at sites of trauma.

Psoriatic arthritis: ~20-30% of patients: asymmetric oligoarthritis, dactylitis ("sausage digit"), enthesitis, axial involvement, DIP joint involvement (distinguishes from RA).

Significant psychosocial impact, associated metabolic syndrome/cardiovascular risk.

Clinical, based on characteristic morphology/distribution. Skin biopsy: rarely needed, reserved for atypical presentation. Screen for psoriatic arthritis at each review (joint symptoms, dactylitis, enthesitis).

Consider metabolic screening (lipids, glucose, BP) given cardiovascular risk association.

Differentials: eczema, tinea corporis, seborrheic dermatitis, lichen planus, cutaneous T-cell lymphoma (mycosis fungoides: consider if atypical/refractory), pityriasis rosea (guttate mimicker).

Severity assessed by BSA and impact (PASI, DLQI).

Mild-moderate (localized):

• Topical corticosteroid + vitamin D analog (calcipotriol) combination: first-line, often once-daily combined product; potent steroid initially, step down

• Topical vitamin D analog alone: maintenance

• Topical tacrolimus/pimecrolimus: for face/flexural (steroid-sparing sites)

• Coal tar preparations, salicylic acid: adjunct for scale removal

• Scalp: tar/salicylic acid shampoo, potent topical steroid scalp application

Moderate-severe (extensive/refractory/significant impact/psoriatic arthritis):

• Phototherapy: narrowband UVB: effective, specialist setting

• Systemic conventional agents: methotrexate 7.5-25mg weekly + folic acid (first-line systemic, also treats PsA), ciclosporin (rapid but not for long-term use: renal/BP monitoring), acitretin (particularly pustular/palmoplantar)

• Biologics (failure of ≥2 conventional systemic therapies or contraindication, per most guidelines): anti-TNF (adalimumab, etanercept, infliximab), anti-IL17 (secukinumab, ixekizumab: highly effective for skin clearance), anti-IL23 (guselkumab, risankizumab), anti-IL12/23 (ustekinumab)

• Pre-biologic screening: TB, hepatitis B/C as per RA entry

Pustular/erythrodermic psoriasis: EMERGENCY-level care: hospitalization, fluid/electrolyte/temperature monitoring, urgent dermatology, avoid abrupt systemic steroid withdrawal (can trigger)

Guttate: often self-limiting, UVB phototherapy if extensive; treat underlying streptococcal infection if active

Lifestyle: smoking cessation, alcohol moderation, weight management, cardiovascular risk factor management, psychological support/counseling for quality of life impact

Referral: dermatology for moderate-severe disease, phototherapy/systemic therapy candidacy; rheumatology for psoriatic arthritis.