Psoriasis

Psoriasis is a common chronic inflammatory skin disorder affecting individuals with an underlying genetic predisposition. The disease manifests following exposure to various triggers (e.g., infection, medication). The typical lesions are sharply demarcated, erythematous, scaly, pruritic plaques, which occur most often on the extensor surfaces of the knees and elbows, but may also affect the scalp and back. Other common clinical findings include involvement of the nails (e.g., pitting or discoloration) or joints, which generally manifests with arthritis of the fingers and lower spine. As psoriasis presents with several subtypes, the size, location, and severity of the lesions vary. The diagnosis is based primarily on clinical findings, but may also be confirmed with tests (e.g., Auspitz sign) or biopsy. Mild psoriasis is treated with topical agents such as steroids, whereas moderate to severe disease requires systemic therapy (e.g., PUVA, biologics).

• Course: relapsing, with symptom-free intervals
• Well-demarcated, erythematous lesions and silvery-white scaling plaques
  • Initially, a few single lesions typically appear, which then often become confluent.
  • Mainly on scalp, back, elbows, and knees (extensor surfaces), but any other site may be involved
  • Pruritus in ∼ 80% of cases (typically mild, but may also be severe)
• Involvement of nails (in ∼ 50% of cases)
  • Nail pitting: small, round depressions in the nail
  • Oil drop sign (or salmon spot): well-circumscribed, yellow-reddish discoloration of the nail
  • Brittle nails: nail dystrophy with crumbling of the nail
  • Onycholysis: partial and mostly distal separation of the nail plate

References:^{[2][3][10][5][11]}

Psoriatic arthritis

• Definition: inflammation of joints (primarily on hands, feet, spine) that may occur with psoriasis
• Epidemiology: 5–30% of psoriasis patients affected
• Clinical features
  • Psoriasis and psoriatic arthritis may occur independently or together
  • There are several types of psoriatic arthritis:
    • Oligoarthritis; (most common, accounting for 70% of cases): typically with involvement of both the distal and proximal interphalangeal joints
    • Spinal involvement (up to 40% of cases)
  • Other rheumatological features
    • Enthesitis
    • Tenosynovitis
    • Dactylitis: inflammation and swelling of fingers or toes (“sausage digit”)
• Diagnosis
  • There is no specific test for diagnosing psoriatic arthritis
  • The ClASsification Criteria for Psoriatic ARthritis (CASPAR); is helpful for diagnosing psoriatic arthritis; (≥ 3 out of the 5 following points required).
    1. Evidence of psoriasis
    2. Psoriatic nail dystrophy
    3. Negative rheumatoid factor (RF)
    4. Dactylitis
    5. Radiologic signs
  • Imaging studies: joint destruction, ankylosis
    • Fingers: pencil-in-cup deformity
    • Spine: syndesmophytes, and in particular asymmetric paravertebral ossification
• Treatment
  • Mild disease: NSAIDs
  • Moderate to severe disease: disease-modifying antirheumatic drugs (DMARDs)
  • Physical therapy

If first-degree relatives of patients with psoriasis have joint problems, psoriatic arthritis should be considered!

Cutaneous variants

• Plaque psoriasis: most common variant characterized by symmetrically distributed, thick, scaly, erythematous lesions
• Guttate psoriasis: lesions the size of drops of water; ; may develop into psoriasis; occurs mainly in children and adolescents after streptococcal infection
• Erythrodermic psoriasis: generalized erythematous lesion with diffuse scaling; ; may lead to severe illness with fever and dehydration
  
• Inverse psoriasis: : mainly affects skin folds and flexural creases of large joints (flexural psoriasis)
• Pustular psoriasis
  • Rare; high correlation with HLA-B27
  • Generalized pustular psoriasis(most common subtype)
    • Generalized erythroderma; confluent, white pustules over the entire body; involvement of oral mucosa and tongue
    • Relapsing course with pronounced malaise (fever, weakness, chills) → possibly fatal!

References:^{[1][12][5][13][14][15][16][17]}

• Koebner phenomenon: Physical stimuli or skin injury (e.g., trauma, scratching, irritating clothing) lead to skin lesions typical of the underlying condition appearing on previously healthy skin ("isomorphic response").
• Auspitz sign: small pinpoint bleeding when scales are scraped off
• Skin biopsy: rarely needed, but may be performed to rule out other diseases
  • Parakeratosis: retention of nuclei in the stratum corneum of the epidermis
  • Munro microabscesses: accumulation of neutrophils in the stratum corneum surrounded by parakeratosis
  • Acanthosis: epidermal hyperplasia of the stratum spinosum
  • Spongiotic dermatitis: epidermal intracellular edema widening the intracellular space between keratinocytes.
    • Epidermal infiltration by lymphocytes is common.
    • Chronic fluid accumulation leads to the formation of intraepidermal vesicles.
• Laboratory tests
  • In case of psoriatic arthritis: ↑ ESR and CRP
  • Rheumatoid factor (RF) negative

References:^[5]

Differential diagnosis of scaling
	Lesion	Distribution
Psoriasis	Clearly demarcated, erythematous plaques with silvery scaling, pruritus	Scalp Extensor surfaces of joints (knees, elbows) Back
Atopic dermatitis	Poorly demarcated, eczema, white scales, severe xerosis and pruritus	Extensor surfaces of extremities (e.g., shins) Flexural creases (antecubital, popliteal)
Seborrheic dermatitis	Clearly demarcated, erythematous plaques, greasy-looking yellow scales	“Cradle cap” in infants Facial involvement (hairline, periocular, nasolabial folds) Trunk
Pityriasis rubra pilaris	Disseminated, plaques with orange-pink scales, hyperkeratosis, erythroderma	Typically palms and soles Islands of unaffected skin (sparing) Follicular keratosis
Erythroderma	Erythema, scaling 2–6 days following onset, lesions of underlying disease, pruritus	Generalized erythema Scaling initially in flexural creases

References:^[5][18]

The differential diagnoses listed here are not exhaustive.

Medical therapy

Mild to moderate psoriasis	Moderate to severe psoriasis	Severe psoriasis
First-line: moisturizers and topical medications Steroids (triamcinolone, fluocinonide, clobetasol) Vitamin D derivatives (calcipotriene) Tar preparations (anthralin) Retinoids/vitamin A derivatives	Topical medication as combination therapy Add systemic agents as needed (methotrexate, retinoid, cyclosporine) Phototherapy	Topical + systemic treatment Phototherapy Biologicals (etanercept, adalimumab, infliximab)

Systemic treatment is always required for psoriatic arthritis (immunosuppressants and NSAIDs)!

Topical treatment	Adverse effects
Topical steroids	Skin atrophy with chronic use Risk: disease flare-up upon discontinuation
Vitamin D derivatives	High doses may cause systemic effects due to the absorption by the skin!
Tar preparations	Dramatic reddening, burning, and skin discoloration possible
Retinoids (vitamin A derivatives)	May cause irritation

Systemic treatment	Examples	Adverse effects
PUVA	PUVA: psoralen + UVA	Long term use Increased risk of skin cancer Premature aging of the skin
Folate antagonists	Methotrexate	Liver and lung toxicity
Retinoids (vitamin A derivatives)	Acitretin	Teratogenic
Immunosuppressant (suppress T cells)	Cyclosporine	Nephrotoxic
Biologicals (TNF-α antagonists)	Etanercept, adalimumab, infliximab	High costs

Phototherapy

Ultraviolet light is effective in treating dermatological conditions, as it has antiproliferative effects (slowing keratinization) and anti-inflammatory effects (inducing apoptosis of pathogenic T cells) on the skin.

• UVA phototherapy
  • Indications: atopic dermatitis, scleroderma, pruritus, prurigo simplex
  • Side effects: less energy intensive and thus less harmful than UVB; however, it leads to skin aging . and is also carcinogenic, but less so than UVB.
• UVB therapy
  • Indications: psoriasis, vitiligo, chronic pruritus, and atopic dermatitis
  • Irradiation with narrowband UVB
  • Accelerates photodamage (e.g., sunburn) and increases cancer risk
• PUVA therapy (psoralen + UVA)
  • Indications: psoriasis, lichen planus, scleroderma, vitiligo, mycosis fungoides
  • Topical (bath, lotions) or oral administration of psoralen → increases photosensitivity of skin → UVA radiation
  • Increases risk of squamous cell carcinoma

References:^{[1][2][12][3][19]}