Dermatology · PANCE / PANRE

Psoriasis

Chronic immune-mediated inflammatory disorder with well-demarcated erythematous plaques and silvery scale; systemic comorbidities.

Also known as: psoriasis, plaque psoriasis, psoriasis vulgaris, guttate psoriasis, inverse psoriasis, pustular psoriasis

Overview

A chronic immune-mediated inflammatory skin disease driven by IL-23/Th17 axis activation, characterized by well-demarcated erythematous plaques with silvery-white scale and frequent involvement of scalp, extensor surfaces, and nails. Systemic disease with cardiometabolic and joint comorbidities.

Epidemiology

Prevalence 2-3% in the US; bimodal onset (16-22 and 57-60 years). Equal sex distribution. ~30% develop psoriatic arthritis (PsA). Strong genetic component — HLA-Cw6 association.

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Risk factors

Family history (40% of patients)
HLA-Cw6 and other PSORS susceptibility loci
Smoking, obesity, alcohol
Streptococcal pharyngitis (triggers guttate psoriasis)
HIV (may unmask or worsen disease)
Medications: beta-blockers, lithium, antimalarials, IFN-α, abrupt systemic steroid withdrawal, ACEi
Koebner phenomenon: trauma, sunburn, tattoo trigger plaques at injured sites
Stress, cold weather

Pathophysiology

Dendritic cell activation → IL-23 production → Th17 polarization → IL-17A, IL-17F, IL-22, TNF-α release → keratinocyte hyperproliferation (turnover accelerated from 28 to 3-5 days), incomplete differentiation (parakeratosis), neutrophil microabscesses (Munro), and dilated dermal vessels (Auspitz sign — pinpoint bleeding when scale removed).

Clinical presentation

Symptoms

Pruritus (often less intense than eczema), burning, soreness
Joint pain, stiffness (PsA) — morning stiffness, dactylitis, enthesitis
Psychosocial impact, depression, sexual dysfunction

Signs / physical exam

Plaque psoriasis (90%): well-demarcated erythematous plaques with adherent silvery scale on extensor elbows, knees, scalp, lumbosacral area, umbilicus
Guttate psoriasis: sudden eruption of small (<1 cm) drop-shaped plaques on trunk and proximal extremities, 1-3 weeks after streptococcal infection; often in children/young adults
Inverse (intertriginous) psoriasis: smooth, glossy, erythematous, scale-poor plaques in axillae, inguinal folds, inframammary, intergluteal
Pustular psoriasis: generalized (von Zumbusch) — sheets of sterile pustules on erythroderma, fever, leukocytosis, life-threatening; palmoplantar — chronic pustules on palms/soles
Erythrodermic psoriasis: >90% BSA erythema and scaling, thermoregulatory failure, high-output cardiac failure — emergency
Nail psoriasis: pitting, oil drop sign, onycholysis, subungual hyperkeratosis, splinter hemorrhages, leukonychia
Scalp psoriasis: thick adherent scale extending beyond hairline

Classic findings

Auspitz sign (pinpoint bleeding after scale removal); Koebner phenomenon (plaques at sites of trauma); silvery micaceous scale.

Differential diagnosis

Seborrheic dermatitis (sebopsoriasis) — Greasy yellow scale in seborrheic distribution; less sharply demarcated; nasolabial folds, eyebrows
Atopic dermatitis — Pruritus prominent, flexural, atopy history, less defined borders
Tinea corporis — Annular with central clearing, raised scaly border; KOH positive
Cutaneous T-cell lymphoma (mycosis fungoides) — Patches/plaques in sun-protected sites in adults; refractory to topical steroids; biopsy
Pityriasis rubra pilaris — Salmon-colored plaques with islands of sparing, follicular hyperkeratosis, waxy palmoplantar keratoderma
Secondary syphilis — Palmoplantar copper-colored macules, condyloma lata, lymphadenopathy; RPR positive
Lichen planus — Purple polygonal pruritic papules with Wickham striae; mucosal involvement
Subacute cutaneous lupus — Photo-distributed annular/psoriasiform plaques; SSA positive

Diagnostic workup

Diagnostic criteria

Clinical diagnosis based on lesion morphology and distribution; severity by BSA, PASI, and impact (DLQI). Mild: BSA <3%; moderate: 3-10%; severe: >10% OR involvement of face, palms/soles, genitals, or nails with disability.

Labs

Clinical diagnosis
Skin biopsy if diagnosis uncertain: parakeratosis, Munro microabscesses, regular acanthosis, thinned suprapapillary plates, dilated tortuous capillaries
Pre-biologic workup: CBC, CMP, hepatitis B/C, TB testing (IGRA or PPD), HIV, pregnancy test; chest X-ray if indicated
PsA screening: PEST or PsAID questionnaire, joint exam at each visit

Imaging

Not routinely indicated for skin disease
Joint X-rays/MRI for suspected PsA: 'pencil-in-cup' deformity, periostitis, ankylosis

Diagnostic algorithm

Subtype	Hallmark	Preferred First-Line
Plaque (vulgaris)	Silvery scale on extensor surfaces, scalp, lumbosacral	Topical steroid + vitamin D analogue; NBUVB or biologic if extensive
Guttate	Drop-shaped lesions post-strep	Treat strep; NBUVB; topical steroid
Inverse	Glossy red plaques in folds	Low-potency steroid, TCI, calcipotriene
Pustular (generalized)	Sheets of sterile pustules, fever	Hospitalize; cyclosporine, infliximab, spesolimab
Erythrodermic	>90% BSA erythema/scale	Hospitalize; cyclosporine, infliximab
Nail	Pitting, oil drop, onycholysis	Intralesional triamcinolone; systemic if associated PsA

Psoriasis subtypes and preferred first-line therapy.

Treatment

First-line

Mild-moderate (limited BSA): topical corticosteroid potency by site — clobetasol 0.05% (high; trunk/extremities, 2 wks then taper), triamcinolone 0.1% (mid), hydrocortisone 1-2.5% (face/folds)
Topical vitamin D analogues — calcipotriene/calcipotriol, calcitriol — often combined with steroid (calcipotriene/betamethasone foam, ointment)
Topical retinoid — tazarotene 0.05-0.1%
Topical calcineurin inhibitors (tacrolimus, pimecrolimus) for face and intertriginous areas
Topical PDE4 inhibitor — roflumilast 0.3% cream daily (FDA-approved, all body areas including folds and face)
Topical AhR agonist — tapinarof 1% cream daily
Coal tar preparations (older) for scalp and plaque psoriasis

Moderate-severe / extensive plaque

Phototherapy: narrowband UVB (first-line for widespread plaque), PUVA (rarely used due to skin cancer risk), targeted excimer laser (308 nm) for localized
Oral systemics: methotrexate 7.5-25 mg/week (folate, monitor LFTs, CBC), cyclosporine 2.5-5 mg/kg/day (short-term, monitor BP/Cr), acitretin 10-50 mg/day (teratogenic, avoid pregnancy 3 years post), apremilast 30 mg BID (PDE4 inhibitor; no monitoring needed), deucravacitinib 6 mg daily (TYK2 inhibitor)
Biologics: anti-TNF — adalimumab, etanercept, infliximab, certolizumab; anti-IL-17 — secukinumab, ixekizumab, brodalumab, bimekizumab; anti-IL-23 — guselkumab, risankizumab, tildrakizumab; anti-IL-12/23 — ustekinumab
Choose biologic by comorbidities: IBD favors anti-IL-23 or anti-TNF (avoid anti-IL-17); PsA favors anti-TNF, anti-IL-17, anti-IL-23, JAK inhibitors

Guttate

Treat strep infection if active
Narrowband UVB highly effective
Topical steroids and vitamin D analogues
Many cases resolve spontaneously within months

Generalized pustular / erythrodermic

Hospitalize; fluid/electrolyte support, temperature regulation
Cyclosporine or infliximab for rapid control
Spesolimab (anti-IL-36R) — FDA-approved for generalized pustular psoriasis flares
Acitretin once stabilized

Second-line / adjunct

Salicylic acid keratolytics (3-6%) to remove scale before topical therapy
Intralesional triamcinolone for nail matrix or isolated plaques
Avoid systemic corticosteroids — rebound and pustular flare on withdrawal

Complications

Psoriatic arthritis — peripheral, axial, dactylitis, enthesitis; permanent joint damage if untreated
Cardiovascular disease — accelerated atherosclerosis, MI, stroke (independent of traditional risk factors)
Metabolic syndrome, obesity, type 2 diabetes, NAFLD
Depression, anxiety, suicidality
Inflammatory bowel disease (Crohn > UC)
Uveitis
Erythroderma and pustular flares — life-threatening
Increased risk of lymphoma (modest), nonmelanoma skin cancer with PUVA
Biologic adverse effects: infection (TB reactivation, HBV reactivation), injection site reactions, candidiasis (anti-IL-17), demyelination (anti-TNF)

PANCE pearls

Never give systemic corticosteroids for psoriasis flare — withdrawal can precipitate pustular or erythrodermic psoriasis.
Auspitz sign (pinpoint bleeding after scale removal) and Koebner phenomenon (lesions at sites of trauma) are classic.
Nail pitting + onycholysis in a patient with joint pain = think psoriatic arthritis even if skin disease is mild.
Anti-IL-17 biologics (secukinumab, ixekizumab) can worsen or precipitate IBD — choose anti-IL-23 or anti-TNF for IBD overlap.
Check IGRA/PPD and HBV serologies before starting any biologic — TB and HBV reactivation are well-described.

References

AAD-NPF 2020-2021 — AAD-National Psoriasis Foundation Joint Guidelines: Biologics, Phototherapy, Topical Therapy, Pediatric Psoriasis, and Comorbidities (Menter et al., J Am Acad Dermatol)
GRAPPA 2021 — GRAPPA Treatment Recommendations for Psoriatic Arthritis (Coates et al., Nat Rev Rheumatol 2022)
NPF Treat-to-Target — From the Medical Board of the National Psoriasis Foundation: Treatment Targets for Plaque Psoriasis (Armstrong et al., J Am Acad Dermatol 2017)

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