The main symptom of ecthyma is a small blister with a red border that may be filled with pus. After the blister goes away, a crusty ulcer appears.
Your doctor can usually diagnose this condition simply by looking at your skin. In rare cases, the fluid inside the blister may be sent to a lab for closer examination or a skin biopsy may be done.
Habif TP. Clinical Dermatology. 4th ed. St. Louis, Mo: Mosby; 2004.
Mandell GL, Bennett JE, Dolin R. Principles and Practice of Infectious Diseases. 6th ed. London: Churchill Livingstone; 2005.
Rakel RE. Textbook of Family Practice. 6th ed. Philadelphia, Pa: WB Saunders; 2002.