Technique
For treating plantar warts, at first paring is done to reduce the thickness of the lesion and determine the size of the wart. This helps in deciding the size of punch required. For all other cryo-amenable conditions, paring is not required. The punch is cut to half the length, and the plastic part is covered with gauze. For smaller punches, a test tube holder is used to hold the punch in place. The punch is kept on the lesion with slight pressure so that there is no gap between the punch metal tip and the skin. This prevents the cryogen from spreading into the normal skin.
The cryocan filled with liquid nitrogen is used. The nozzle is kept on the top end of the punch. Note that when the punch is cut, the edge should be smooth and flat so that the nozzle sits perfectly on it. The liquid nitrogen is passed, and as the liquid nitrogen spray touches the lesion through the punch, the metal tip of the punch also gets cooled, which then slowly starts sinking into the lesion [Figure 2]. For the treatment of warts, freezing is continued till the bevelled edge of the punch enters the skin. When deeper cryotherapy is required, the punch is driven further inside the lesion. This helps in deeper delivery of the cryogen and increases efficacy, with least damage to the surrounding tissue. The punch need not be rotated to cut into the lesion; rather the effect of cooling itself makes the punch cold cut into the lesion [Video 1 online at www.jcasonline.com].
Figure 2  The procedure being performed. 1. Metal tip of punch in contact with the skin. 2. Gauze surrounding the punch for grip. 3. Test tube holder to hold the punch firmly. 4. The nozzle of cryocan kept onto the top of the punch Click here to view as Video 1   The punches remain embedded till they are frozen [Figure 3]. The punches fall off on their own in 10-20 seconds depending on the depth reached. The next punch can be placed adjacent to the previous punch and the process is repeated. The procedure can be performed two or three times on the same lesion depending on its size. In keloids,[2] the cryogen can be sprayed longer with least damage to surrounding normal tissue. This technique is useful even in larger lesions like keloid where it can be sprayed into multiple areas with less pain and damage to the tissues. Following the procedure, no dressing is required. Pain killers or anti-inflammatory drugs can be prescribed. In case blister occurs, which is very rare, the fluid collected can be expressed out with a needle or syringe.
Figure 3  The punches remain embedded, note the cryo surrounding the punch is minimal. Two punches are placed one beside the other