Differential diagnosis of round or discoid lesions.

Dermatologists are called on to diagnose a variety of skin conditions in diverse age groups. Dermatologic diagnosis, based on identification of a primary lesion, uses morphologic clues to categorize the pathologic process causing the eruption. In addition, distribution and grouping of lesions helps support a specific diagnosis. Dermatologists consciously or unconsciously use pattern recognition to arrive at their differential diagnosis based on clinical experience and their having previously viewed similarly appearing skin lesions in lectures, texts, and journals. Round and discoid patches and plaques are extremely common in the clinical practice of dermatology. This contribution reviews the dermatologic conditions that present as round or discoid lesions and presents an approach to diagnosis.