How can I distinguish seborrheic dermatitis from psoriasis and what are the appropriate treatments for each?

Distinguishing Seborrheic Dermatitis from Psoriasis

Seborrheic dermatitis presents with greasy yellowish scaling on sebaceous areas (scalp, central face, ears) with intense itching, while psoriasis shows well-demarcated thick plaques with silvery-white scale, minimal pruritus, and symmetric distribution—these are fundamentally different conditions requiring distinct treatment approaches. 1, 2, 3

Clinical Differentiation

Seborrheic Dermatitis Features

• Appearance: Greasy, yellowish scaling with poorly-defined erythematous patches 1, 4
• Distribution: Scalp, central face, ears, and other sebaceous skin areas 1, 5
• Symptoms: Intense itching is prominent 1
• Scale quality: Oily, yellow, greasy scale (not dry or silvery) 1, 4
• Associated findings: Secondary inflammation from Malassezia yeast colonization 1, 5
• Risk factors: More pronounced in Down syndrome, HIV infection, and Parkinson's disease 1

Psoriasis Features

• Appearance: Well-demarcated, thick hyperkeratotic plaques with silvery-white scale 2, 3
• Distribution: Uniform and symmetric distribution; plaques are sharply defined 2, 3
• Symptoms: Minimal to moderate itching—pruritus is NOT a dominant feature 3
• Scale quality: Dry, thick, silvery scale without oozing or weeping 3
• Plaque characteristics: Indurated plaques with characteristic silvery scale on trunk 1
• Histopathology (when needed): Mounds of parakeratosis with neutrophils, spongiform micropustules of Kogoj, clubbed and evenly elongated rete ridges, increased mitotic figures (≥6/high-powered field) 6

Key Distinguishing Points

• Pruritus intensity: Seborrheic dermatitis has intense itching as primary complaint; psoriasis has minimal pruritus 1, 3
• Scale appearance: Greasy yellow (seborrheic) versus dry silvery-white (psoriasis) 1, 2, 3
• Border definition: Poorly-defined patches (seborrheic) versus well-demarcated plaques (psoriasis) 2, 3
• Oozing/crusting: Absent in both, but seborrheic dermatitis may show secondary inflammation 1, 3

Common pitfall: When both conditions occur on the scalp without other body involvement, differential diagnosis becomes challenging—look for the quality of scale (greasy vs. silvery) and degree of pruritus as primary discriminators 4, 6

Treatment for Seborrheic Dermatitis

First-Line Approach

• Topical antifungals to reduce Malassezia yeast colonization 1, 5
  • Ketoconazole 2% cream applied to affected areas twice daily for 4 weeks 7
  • Continue until clinical clearing is achieved 7
• Topical anti-inflammatory agents to reduce inflammation and itch 1, 5
  • Low-to-medium potency corticosteroids for short-term use 1
  • Calcineurin inhibitors (tacrolimus 0.1% ointment or pimecrolimus 1% cream) for maintenance 1

Emerging Options

• Roflumilast 0.3% foam (topical phosphodiesterase-4 inhibitor) provides effective non-corticosteroid option 5

Maintenance Strategy

• Continue antifungal therapy intermittently to prevent recurrence 5
• Address skin barrier dysfunction with gentle skin care and emollients 1

Treatment for Psoriasis

Mild Psoriasis (≤5% Body Surface Area)

Initial therapy: High-potency topical corticosteroids combined with calcipotriene (vitamin D analog) 2, 8, 3

Body Plaques

• Clobetasol propionate 0.05% or betamethasone dipropionate 0.05% twice daily for maximum 2-4 weeks 2, 8, 3
• Add calcipotriol for synergistic effect superior to monotherapy, achieving 58-92% clearance rates 2, 8
• Fixed-combination products: Calcipotriene/betamethasone dipropionate gel or foam once daily for 4-12 weeks 8
• Alternative regimen: Apply high-potency corticosteroid in morning and vitamin D analog in evening 8

Scalp Involvement

• Clobetasol propionate 0.05% shampoo twice weekly, providing rapid symptom relief within 3-4 weeks 8

Face, Genitals, Intertriginous Areas

• Low-potency corticosteroids or topical calcineurin inhibitors to minimize atrophy risk 8, 3

Maintenance Phase

• Transition to weekend-only corticosteroid application with vitamin D analogs on weekdays after achieving control to prevent tachyphylaxis 2, 3

Alternative Topical Option

• Coal tar preparations: Start at 0.5-1.0% crude coal tar in petroleum jelly, increasing to maximum 10% as tolerated 2, 3

Moderate-to-Severe Psoriasis (>5% Body Surface Area)

Escalate to systemic therapy when: Body surface area exceeds 5%, inadequate response to optimized topical therapy after 8 weeks, or signs of erythrodermic or pustular psoriasis develop 8

Systemic Treatment Options (in order of consideration)

1. Photochemotherapy (PUVA): Least toxic systemic agent, first-line systemic treatment; starting dose at 70% of minimum phototoxic dose 8

2. Cyclosporin: Response time 3 weeks; initial dose 2.5 mg/kg/day divided twice daily, increase by 0.5 mg/kg/day every 2 weeks to maximum 4 mg/kg/day 8, 9

   • 51% achieve 75% improvement by 8 weeks, 79% by 16 weeks 9
   • Contraindicated with abnormal renal function, uncontrolled hypertension, or malignancy 8

3. Methotrexate: Response time 2 weeks; absolute contraindications include pregnancy, breastfeeding, wish to father children, significant hepatic damage, anemia, leucopenia, thrombocytopenia 8

4. Acitretin: Response time 6 weeks; requires contraception with absolute contraindication for pregnancy or wish to conceive within 2 years of stopping 8

5. Infliximab: For generalized pustular psoriasis—demonstrates rapid and often complete clearance; 5 mg/kg infused at weeks 0,2, and 6, then every 8 weeks 8

Critical Safety Warnings

Absolute Contraindications for Psoriasis

• NEVER use systemic corticosteroids for psoriasis—they precipitate erythrodermic or generalized pustular psoriasis upon discontinuation, which can be severe and potentially fatal 2, 8, 3

Medications to Avoid in Psoriasis Patients

• Beta-blockers, NSAIDs, lithium, chloroquine, mepacrine: May cause severe, potentially fatal psoriasis deterioration 2, 8, 3
• Alcohol: Can precipitate or worsen psoriasis 8
• Salicylic acid with calcipotriene: Acidic pH inactivates calcipotriene and reduces effectiveness 8

Corticosteroid Safety Monitoring

• Mandatory clinical review every 4 weeks during active treatment with no unsupervised repeat prescriptions for high-potency agents 2, 8, 3
• Limit moderate-potency corticosteroid use to maximum 100g per month 2, 8, 3
• Require dermatological supervision for class 1-2 preparations 8
• Decrease dose by 25-50% to control adverse events (hypertension, serum creatinine elevation ≥25% above baseline) 9

Common Pitfall

Perceived treatment failure is often due to poor adherence rather than true drug resistance—address compliance issues before switching therapies 2