Psoriasis is a common chronic inflammatory skin disorder affecting individuals with an underlying genetic predisposition. Triggering events (e.g., infection, medication) can lead to disease manifestation. Psoriasis typically manifests as sharply demarcated, erythematous, scaly, pruritic plaques, most commonly occurring on the scalp, presacral region, and extensor surfaces of the knees and elbows; however, any area of the skin may be affected. Other common clinical findings include arthritis, generally affecting the fingers and lower spine, and nail involvement (e.g., pitting, discoloration). The size, location, and severity of psoriasis lesions vary depending on the subtype. The diagnosis is primarily clinical, based on the patient's symptoms, history, and the presence of any specific signs (e.g., the Auspitz sign); a biopsy is rarely indicated. Mild psoriasis can be treated with topical agents such as corticosteroids, whereas moderate to severe disease requires systemic therapy (e.g., phototherapy, biologic agents).
- Prevalence: ∼ 2% of the US population 
Age of onset: : can present at any age; typically shows bimodal age distribution 
- Early onset psoriasis: (∼ 75% of cases): before 40 years of age
- Late onset psoriasis (∼ 25% of cases): after 40 years of age; usually mild
Epidemiological data refers to the US, unless otherwise specified.
The mechanism causing the immune response is not yet well understood.
- Increased proliferation of keratinocytes
- T cells secrete cytokines, which mediate an inflammatory response.
The disease course is typically relapsing, with symptom-free intervals.
Cutaneous lesions 
- Well-demarcated, erythematous plaques and/or papules with silver-white scaling
- Typically, a few single lesions initially appear, often becoming confluent. 
- Located mainly on the scalp, trunk, elbows, and knees (extensor surfaces), but any area of the skin may be affected.
- Pruritus in ∼ 80% of cases (typically mild, but may be severe in some cases) 
Characteristic features may be present.
- Small pinpoint bleeding when scales are scraped off
- Removal of the scales exposes the dermal papillae, which leads to bleeding.
- Koebner phenomenon: Physical stimuli or skin injury (e.g., trauma, scratching, irritating clothing) can lead to the appearance of psoriatic skin lesions on previously unaffected skin (isomorphic response). 
- ; 
Cutaneous variants 
- Plaque psoriasis: most common variant; characterized by symmetrically distributed, thick, scaly, erythematous lesions
- Guttate psoriasis
- Erythrodermic psoriasis
- Inverse psoriasis: : mainly affects skin folds and flexural creases of large joints (flexural psoriasis)
- Pustular psoriasis
Plaque psoriasis is the most common psoriasis variant (accounts for ∼ 80–90% of psoriasis cases). 
Nail involvement 
Present in ∼ 50% of cases 
- Nail pitting: small, round depressions in the nail
- Brittle nails: nail dystrophy with crumbling of the nail
- Onycholysis: partial and mostly distal separation of the nail plate
- Oil drop sign (or salmon spot): well-circumscribed, yellow-red discoloration of the nail 
Psoriasis and PsA can occur together or alone
Clinical features 
Multiple patterns may be present.
- Oligoarthritis; (typically asymmetric; ≤ 4 joints affected)
- Polyarthritis (symmetric; similar appearance to )
- Involvement of distal and proximal interphalangeal joints ( and ); often occurs in conjunction with other subtypes 
- Arthritis mutilans: destruction of interphalangeal joints through bone resorption, resulting in the collapse of the soft tissue of the affected area (e.g., telescoping fingers or “ ”)
- Axial involvement (spine and sacroiliac joints); often occurs in conjunction with other subtypes
Accompanying features 
- Enthesitis, e.g., of the calcaneal tendon or the plantar fascia 
- Dactylitis: inflammation and swelling of the fingers and/or toes (“sausage digits”) 
- Nail involvement (e.g., pitting, onycholysis) 
In PsA, patterns of joint involvement can change over time and vary widely between patients. Oligoarthritis tends to be more common at onset, while polyarthritis may develop in later stages. 
- Diagnosis is mainly clinical, based on patient and family history and clinical features.
- lmaging studies can support the diagnosis and help estimate severity.
- Laboratory studies are usually obtained as a part of the inflammatory arthritis workup.
- Consult rheumatology for all patients.
Imaging studies 
- X-ray of the affected area (e.g., hands, spine)
- Further studies
Laboratory studies 
Laboratory studies may be obtained to rule out other diagnoses but are not typically required to make a diagnosis of PsA.
- Inflammatory markers: ↑ ESR, ↑ CRP 
- BMP: ↑ uric acid
Rheumatoid factor is typically negative in patients with PsA, which can help rule out . 
These classification criteria are not diagnostic but can provide guidance in clinical practice. 
|Classification criteria for psoriatic arthritis (CASPAR) |
|Clinical features|| ||2|
|Diagnostic studies|| ||1|
A total score of ≥ 3 points indicates PsA.
- Treatment depends on disease severity and the presence of certain features and/or comorbidities.
- A treat-to-target approach with a target of remission or low disease activity is recommended. 
- Consult a rheumatologist before starting pharmacotherapy.
Pharmacological treatment 
- Disease-modifying antirheumatic drugs (DMARDs): mainstay of treatment for most patients with PsA.
- NSAIDs, e.g., naproxen, indomethacin:
- Intraarticular glucocorticoids: used for symptomatic relief
Systemic glucocorticoids are not commonly used in PsA because of concerns that tapering too rapidly may induce a flare of cutaneous disease. 
Supportive management 
- Consult a dermatologist to confirm the diagnosis.
- Skin biopsy is not routinely required for diagnostic confirmation.
- Perform an . 
- Evaluate for comorbidities including psoriatic arthritis, IBD, MDD, and anxiety.
Skin biopsy 
|Differential diagnosis of scaling|
|Atopic dermatitis|| |
|Pityriasis rubra pilaris|| |
The differential diagnoses listed here are not exhaustive.
The following recommendations apply to the treatment of plaque psoriasis ; consult a specialist before initiating treatment.
Approach to patients with psoriasis
Treatment depends on disease severity, comorbidities, and patient preference.
- Assess disease severity: e.g., based on (BSA) affected.
- Provide supportive care.
- Mild psoriasis (below 3–5% BSA involvement)
Moderate to severe psoriasis (above 3–5% BSA involvement)
- Systemic pharmacotherapy
- Consider adjunctive topical pharmacotherapy.
Topical pharmacotherapy 
Topical pharmacotherapy is the mainstay of mild psoriasis treatment.
- (first-line: )
- Topical calcineurin inhibitors (off-label use ): e.g., 0.03 % or 0.1%, or 1%
- Additional therapy: the following agents may be used in combination with topical corticosteroids
Commonly used combinations include topical corticosteroids plus either vitamin D analogues or keratolytic agents. Combination therapy increases efficacy and may cause fewer adverse effects than monotherapy.
Systemic pharmacotherapy 
- Principles of systemic therapy
- Moderate to severe psoriasis
- Mild psoriasis with insufficient response to topical agents
- Treatment options
Supportive care 
- Provide topical treatment with ointments (e.g., petroleum jelly) and moisturizers to prevent moisture loss.
- Counsel on reducing alcohol consumption and smoking cessation.
- Provide management for any comorbid mental health conditions (e.g., MDD, anxiety).
- 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.