creation date: 2026-02-06 19:37
tags: PathologiesIncomplete
Psoriasis
Background
Definitions
Psoriasis is a chronic inflammatory skin condition. A number of subtype exist, the most common of which is chronic plaque psoriasis.
Risk Factors
A number of risk factors are proposed to predispose a patient to psoriasis.
Genetics:
- 40% of patients with psoriasis have a family history
- Genes involved with MHC, HLA, IL23
Other factors include:
- Smoking
- Obesity
- Alcohol use
Psoriasis may also be worsened or cause eruptions by:
- Drugs such as beta blockers, lithium, antimalarial drugs
- Infections
- Low vitamin D
- Stress (unclear link)
Pathophysiology
Psoriasis is a disease involving complex immune-mediated hyperproliferation. It involves T lymphocytes, dentritic cells, cytokines, and other inflammatory markers.
Antigenic stimuli, such as medications, alcohol, trauma, smoking, stress, and infection, causes the activation of innate immune cells in the skin. An inflammatory cascade is triggered through proinflammatory cytokines. Subsequent activation of adaptive immune response causes further inflammatory changes and vasodilatation.
This state is hyperproliferative and is characterized by:
- Increased epidermal stem cells
- Increased number of cells undergoing DNA synthesis
- Shortened cell cycle time for keratinocytes (10% of normal skin)
- Decreased turnover time of the epidermis (4 compared to 27 of normal skin)
- Abnormal differentiation of epidermis
The hyperproliferative state results in the typical clinical findings.
Clinical Presentation
Signs & Symptoms
There are four major subtypes of psoriasis with varying manifestations.
Chronic plaque psoriasis
- Symmetrically distributed, cutaneous plaques
- Plaques are erythematous with sharply defined margins; erythema may be hidden in highly pigmented skin
- Common sites: scalp, extensor elbows, knees, gluteal cleft
- Commonly pruritic but may be asymptomatic
Classic signs of chronic plaque psoriasis that are neither sensitive nor specific include:
- Koebner phenomenon (prior skin trauma causing disease)
- Auspitz sign (pinpoint bleeding after removal of scale)
Gluttate psoriasis (gluttate = “drop-like”)
- Abrupt appearance of small, psoriatic papules and plaques
- Typically occurs without history of psoriasis but may be flare of pre-existing
- Associated with recent infection (streptococcal pharyngitis)
Pustular psoriasis
- Widespread erythema, scaling, and sheets of superficial pustules
- May be associated with malaise, fever, diarrhea, leukocytosis, hypocalcemia
- Associated complications include renal, hepatic, respiratory abnormalities, and sepsis
Erythrodermic psoriasis
- Generalized erythema and scaling involving most or all of the body surface
- Inadequate barrier protection
Special sites
Psoriasis that involves intertriginous skin, nails, palms, or soles may exhibit unique features.
Inverse (intertriginous) psoriasis:
- Inguinal, perineal, genital, intergluteal, axillary, or inframammary regions
- Well-demarcated, smooth, shiny plaques
- Absent or minimal scales
Nail psoriasis:
- Pitting over nail plate, leukonychia, red spots on lunula, crumbling of nail plate
- Colour change of nail (if nail bed is involved) looking like new motor oil (“oil drop sign”)
Palmoplantar psoriasis:
- Erythematous, hyperkerototic plaques on palm or soles
- May have fissures (painful and may be disabling)
History & Physical Exam
Components to include in history include:
- Family history
- Exposure to exacerbating medications
A full skin examination including scalp, nail, and anogenital skin exam should be offered.
Diagnosis
Criteria
Diagnosis can generally be made clinically by physical exam.
A skin biopsy may be helpful but usually not necessary for chronic plaque psoriasis. For other subtypes of psoriasis, histological findings may be necessary to support the diagnosis.
Work-up
Skin biopsy
Should it be necessary a skin biopsy typically consist of a 4mm punch biopsy from the involved skin. A shave biopsy may be adequate in some cases.
A PAS-D stain of the specimen may be used to distinguish psoriasis from supficial fungal infection.
Further assessment
Patients should be screened for signs/symptoms of psoriatic arthritis and other comorbidities.
Differential
Key diagnoses that may be mistaken for chronic plaque psoriasis include:
- Seborrheic dermatitis (eval: fine, greasy scale)
- Lichen simplex chronicus (eval: hx of scratching; thickening)
- Atopic dermatitis
- Nummular eczema
- Superficial fungal infections
Red Flags / Complications
Psoriasis increases the risk of several conditions. This includes:
- Psoriatic arthritis
- Comorbid diseases including cardiovascular, malignancy, diabetes, hypertension, IBD, and more
- Ocular disease
Management
The management discussed here will be for chronic plaque psoriasis. Management of other subtypes may vary.
There is no cure for chronic plaque psoriasis but treatment is used to improve signs and symptoms.
Treatment options consist of:
Topical therapies
- Topical corticosteroids
- Vitamin D analogs
- Calcineurin inhibitors
Systemic therapies
- Anti-TNF-alpha, anti-IL17, and anti-IL23 biologic agents
Phototherapy
- Narrowband UV-B
- Psoralen plus UV-A
Selection of mode of therapy depends on several factors:
-
Extent and location of skin involvement
-
Disease complications
-
Comorbidities
-
Preference and availability
-
Response to prior therapies
Generally, a topical therapy is used initially but consideration of systemic therapy should be done if there is difficulty in application, risk of inadequate response, or if regimen is not feasible for long term.