Disease	Distinguishing features
Seborrheic dermatitis	Greasy, scaly lesions, absence of family history
Psoriasis	Localized patches on extensor surfaces, scalp, buttocks; pitted nails
Neurodermatitis	Usually, a single patch in an area accessible to itching; absence of family history
Contact dermatitis	Positive exposure history, rash in area of exposure, absence of family history
Scabies	Papules, finger web involvement, positive skin scraping
Systemic diseases	Findings on complete history and physical examination vary by disease
Dermatitis herpetiformis	Vesicles over extensor areas and associated enteropathy
Dermatophyte infection	Serpiginous plaques with central clearing, positive potassium hydroxide preparation
Immunodeficiency disorder	History of recurrent infection