- Clinical science
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).
- Prevalence: ∼ 2% of the white population
- Age of onset: 20–40 years
Epidemiological data refers to the US, unless otherwise specified.
- Genetic predisposition: : most likely determined via polygenic inheritance
- Trigger factors
|Psoriasis type I||Psoriasis type II|
|Onset||Early onset||Late onset|
|Prevalence||60–70% of cases||30–40% of cases|
|Genetic predisposition||Relatives often affected||Relatives rarely affected|
|Correlation with HLA||Strong association with HLA (HLA-Cw6, HLA-B17 and HLA-B57)||Rarely correlated with HLA|
|Clinical presentation||Often severe disease||Usually mild disease|
- Increased proliferation of keratinocytes
T cells secrete cytokines, which mediate an inflammatory response.
- The mechanism causing the immune response is not yet well understood.
- Course: relapsing, with symptom-free intervals
- Well-demarcated, erythematous lesions and silvery-white scaling plaques
- Involvement of nails (in ∼ 50% of cases)
- Definition: inflammation of joints (primarily on hands, feet, spine) that may occur with psoriasis
- Epidemiology: 5–30% of psoriasis patients affected
- 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
- Dactylitis: inflammation and swelling of fingers or toes (“sausage digit”)
- 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).
- Imaging studies: joint destruction, ankylosis
If first-degree relatives of patients with psoriasis have joint problems, psoriatic arthritis should be considered!
- 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
- 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
- : retention of nuclei in the stratum corneum of the epidermis
- Munro microabscesses: accumulation of neutrophils in the stratum corneum surrounded by parakeratosis
- : epidermal hyperplasia of the stratum spinosum
- epidermal intracellular edema widening the intracellular space between keratinocytes. :
- Laboratory tests
|Differential diagnosis of scaling|
|Atopic dermatitis|| |
|Seborrheic dermatitis|| |
|Pityriasis rubra pilaris|| |
The differential diagnoses listed here are not exhaustive.
|Mild to moderate psoriasis||Moderate to severe psoriasis||Severe psoriasis|
|Topical treatment||Adverse effects|
|Topical steroids|| |
|Vitamin D derivatives|| |
|Tar preparations|| |
|Retinoids (vitamin A derivatives)|| |
|Systemic treatment||Examples||Adverse effects|
PUVA: psoralen + UVA
|Retinoids (vitamin A derivatives)||Acitretin|| |
|Immunosuppressant (suppress T cells)||Cyclosporine|| |
|Biologicals (TNF-α antagonists)||Etanercept, adalimumab, infliximab|| |
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
- UVB therapy
- PUVA therapy (psoralen + UVA)
- Lifelong disease, usually benign
- Patients may experience remissions of varying lengths; acute episodes of exacerbation possible.
- Psoriasis is associated with depression and a decreased quality of life.
- Avoidance of nicotine and alcohol
- Regular physical activity