Anyone ever heard of doing an incisional biopsy to diagnose skin rash?

Punch biopsy. Punch biopsy is considered the primary technique to obtain diagnostic, full-thickness skin specimens. It is performed using a circular blade or trephine attached to a pencil-like handle. The instrument is rotated down through the epidermis and dermis, and into the subcutaneous fat. The punch biopsy yields a cylindrical core of tissue that must be gently handled (usually with a needle).