What are the indications for punch biopsies?

A punch biopsy utilizes a round knife that takes a cylinder of tissue including the epidermis, dermis, and often the subcutaneous fat. Although punch biopsies from 2 to 10 mm in diameter can be used, the most common diameter is 4 mm. A larger punch biopsy may be useful if the specimen is to be divided for culture or other procedures. When splitting the biopsy, the specimen is cut through the dermal rather than the epidermal side to reduce crush artifact. A larger punch biopsy of the skin is also helpful in the diagnosis of cutaneous T-cell lymphoma and for scalp biopsies, where a generous specimen is often necessary to establish the diagnosis. The surgical defect left by punch biopsies may be allowed to heal-in secondarily, but most dermatologists close the defect with a single suture.