Differential diagnosis includes Seborrheic dermatitis Dermatophytoses (potassium hydroxide wet mount should be done for any scaly plaques, especially if they do not have a classic appearance of eczema or psoriasis) Cutaneous lupus erythematosus Eczema Lichen planus Allergic contact dermatitis Pityriasis rosea Squamous cell carcinoma in situ (Bowen disease, especially when on the trunk; this diagnosis should be considered for isolated plaques that do not respond to usual therapy) Lichen simplex chronicus Secondary syphilis Biopsy is rarely necessary and may not be diagnostic; however, it may be considered in cases where the clinical findings are not classic.