How is psoriasis diagnosed and treated?

How to Confirm Psoriasis

Psoriasis is diagnosed clinically based on the presence of characteristic well-demarcated, erythematous plaques with silvery-white scale, typically on extensor surfaces (elbows, knees, scalp, presacral region), without requiring laboratory investigations or biopsy in most cases. 1, 2

Clinical Diagnostic Criteria

The diagnosis relies on pattern recognition of specific morphologic features 3:

• Plaque characteristics: Well-demarcated, raised erythematous plaques covered with silvery-white scale that distinguish psoriasis from other dermatoses 1
• Distribution pattern: Classically involves extensor surfaces (elbows, knees), scalp, and presacral region, though any skin area may be affected including palms, soles, nails, and genitalia 4
• Nail findings: Pitting, onycholysis, oil spots, and subungual hyperkeratosis strongly support the diagnosis, particularly when associated with distal interphalangeal joint disease 1

When Biopsy May Be Helpful

Histopathological examination is generally not required for typical presentations but may be valuable when clinical features are atypical or the diagnosis is uncertain. 3, 5

• Biopsy is indicated for atypical presentations, controversial cases, or when differentiating psoriasis from other dermatoses 5
• Classic histologic features include epidermal hyperproliferation, parakeratosis, and inflammatory infiltrates 5
• The diagnosis remains primarily clinical even when histopathology is available 3

Severity Assessment After Diagnosis

Once psoriasis is confirmed, assess severity at every visit 1:

• Body Surface Area (BSA): <3% = mild, 3-10% = moderate, >10% = severe disease 4
• Patient-reported disability: The patient's perception of treatment need is essential regardless of BSA 1
• Location-based severity: Psoriasis can be severe irrespective of BSA when involving hands, feet, scalp, face, genitalia, or causing intractable pruritus 4
• PASI score: Ranges 0-72, with ≥10 indicating moderate-to-severe disease; primarily used in clinical trials, rarely in practice 4, 1

Essential Screening After Diagnosis

All patients with confirmed psoriasis must be screened for psoriatic arthritis and systemic comorbidities to prevent irreversible complications. 1

Musculoskeletal Screening

• Screen for morning joint stiffness, joint swelling, and enthesitis at every visit 1
• 15-30% of psoriasis patients develop psoriatic arthritis, and failure to screen leads to irreversible joint damage 1
• Refer to rheumatology immediately if any joint symptoms are present 1

Comorbidity Evaluation

• Assess cardiovascular risk factors, mental health status, and inflammatory bowel disease 1
• Recognize psoriasis as a chronic multisystem inflammatory disorder associated with metabolic syndrome, cardiovascular disease, obesity, and diabetes 4, 2

Critical Pitfalls to Avoid

• Never perform routine laboratory tests or biopsies for typical plaque psoriasis presentations – the diagnosis is clinical 1, 3
• Do not miss joint symptom screening – this leads to irreversible psoriatic arthritis damage 1
• Avoid medications that worsen psoriasis: beta-blockers, NSAIDs, lithium, antimalarials (chloroquine, mepacrine) can precipitate severe, potentially fatal deterioration 1, 6
• Never use systemic corticosteroids – they can precipitate severe flare-ups upon discontinuation 6

When to Refer to Dermatology

Referral is indicated for 1:

• Uncertain diagnosis requiring expert evaluation
• Moderate-to-severe disease (BSA ≥10%)
• Failure of topical therapy after 4 weeks
• Need for systemic agents or phototherapy