Eczema and Psoriasis: Clinical Diagnosis
Both eczema and psoriasis are diagnosed clinically based on history, physical examination, and characteristic clinical features—skin biopsy is generally not required for typical presentations. 1, 2
Atopic Eczema (Atopic Dermatitis)
Atopic eczema is diagnosed clinically without biopsy. 1 The diagnosis requires:
- An itchy skin condition (or report of scratching/rubbing in children) 1
- Plus three or more of: history of flexural involvement, personal/family history of atopy, generalized dry skin, visible flexural eczema, or onset in first two years of life 1
A skin biopsy is generally not helpful in diagnosing atopic eczema. 1
When to Consider Alternative Diagnoses
If diagnostic uncertainty exists, consider other conditions such as:
- Scabies (look for burrows in finger webs) 1
- Immunodeficiency states (recurrent systemic or ear infections, petechiae) 1
- Contact dermatitis (may develop in patients with pre-existing eczema) 1
Psoriasis
Psoriasis is diagnosed clinically based on characteristic erythematous, scaly plaques with silvery scale, typically on extensor surfaces, without requiring laboratory investigations in most cases. 2
Key Diagnostic Features
- Well-demarcated, raised erythematous plaques covered with silvery-white scale 2
- Nail involvement (pitting, onycholysis, oil spots, subungual hyperkeratosis) supports the diagnosis, particularly with distal interphalangeal joint disease 2
- Distribution pattern on extensor surfaces distinguishes psoriasis from eczema 3
When Biopsy May Be Indicated
Skin biopsy is reserved for atypical presentations or diagnostic uncertainty, particularly when differentiating from conditions that can mimic psoriasis: 1
- Erythrodermic psoriasis may closely resemble atopic dermatitis, contact dermatitis, seborrheic dermatitis, cutaneous T-cell lymphoma, or pityriasis rubra pilaris both clinically and histologically 1
- Atypical psoriasis plaques in groin or buttock areas should raise suspicion for cutaneous T-cell lymphoma and warrant complete lymph node examination and skin biopsy 1
- Eczematized psoriasis (occurring in 5-10% of psoriasis patients) presents diagnostic challenges with overlapping features and may benefit from histologic confirmation 4, 5, 6
Critical Diagnostic Pitfalls
- Don't rely solely on location: Psoriasis can be severe regardless of body surface area when it causes serious emotional consequences or occurs in selected locations 7
- Screen for psoriatic arthritis: All patients with cutaneous psoriasis should be informed about the association with psoriatic arthritis and screened for musculoskeletal symptoms 2
- Consider medication triggers: Beta-blockers, NSAIDs, lithium, and antimalarials can precipitate or severely worsen psoriasis 2, 7, 3
- Examine the entire body: Inspection of the entire body surface and detailed history are essential for establishing the diagnosis, particularly for scalp involvement 8
When to Refer for Specialist Evaluation
Referral to dermatology is indicated for: 2
- Uncertain diagnosis
- Moderate-to-severe disease
- Failure of topical therapy
- Need for systemic agents or phototherapy