Erythematous scaly plaques with silvery borders on extensor surfaces and nail pitting. Most likely diagnosis and initial therapy?

• A. Atopic dermatitis
• B. Seborrheic dermatitis
• C. Plaque psoriasis; treat with topical corticosteroids and consider phototherapy or systemic therapy for extensive disease
• D. Guttate psoriasis

Answer: (C)

This presentation is classic for plaque psoriasis: well-demarcated erythematous plaques with silvery scales on extensor surfaces, often accompanied by nail changes such as pitting. Nail pitting is a clue that points toward psoriasis rather than eczema or seborrheic dermatitis, which have different patterns of involvement and appearance. Atopic dermatitis typically shows itching and flexural, lichenified lesions, while seborrheic dermatitis presents with greasy scales in areas like the scalp and face. Guttate psoriasis tends to present as many small, drop-like lesions after a streptococcal infection and usually lacks the prominent nail changes seen here.

For initial therapy, start with topical corticosteroids to reduce inflammation and rapid keratinocyte turnover. In more extensive disease, add phototherapy (such as narrowband UVB) or escalate to systemic therapies (e.g., methotrexate, cyclosporine, retinoids, or biologics) depending on severity and response.