Diagnosis is primarily based on the appearance of the skin and on personal and family history. The health care provider should examine the lesions to rule out other possible causes. A skin lesion biopsy may be performed, but is not always required to make the diagnosis.
Habif TP. Clinical Dermatology. 4th ed. St. Louis, Mo: Mosby; 2004:41.
Goldman L, Ausiello D. Cecil Textbook of Medicine, 22nd ed. Philadelphia, Pa: WB Saunders; 2004:2458-2460.