Dermatology Online Journal

Frostbite following use of a commercially available cryotherapy device for the removal of viral warts
Sammut SJC, Brackley PTH, Duncan C, Kelly M, Raraty C, Graham K
Dermatology Online Journal 14 (6): 9

Burns Unit, Department of Plastic and Reconstructive Surgery, Royal Liverpool Children's Hospital, Alder Hey, Eaton Road, Liverpool, UK. john.sammut@gmail.com

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Abstract

Warts are a common skin complaint in childhood. We describe 3 unusual cases in which inadvertent tissue injury was caused during the treatment of viral warts by a commercially available cryotherapy device. In each case there was a failure to follow the instructions provided correctly. If such devices are to remain available for public use we feel changes should be implemented to reduce the risk of such injuries occurring again in the future. Alternatively, cryotherapy as a treatment modality should remain in the realm of the trained health care professional.

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Introduction

A burn is the result of tissue injury caused by direct chemical, electrical, radiational or thermal sources; the severity of the sustained injury is determined by both the properties of and duration of exposure to the primary source. Thermal injuries are the most commonly encountered within the burn unit and the vast majority of these are the result of exposure to high temperatures. However, a small percentage of burns result from exposure to cold sources (i.e. cold burn/frostbite). The exact incidence of cold-induced injuries is difficult to determine as only the most severe cases present to hospital [1].

The degree of tissue damage in a burn resulting from thermal injury is proportional to the amount of energy transferred, to or from a given tissue area. This is determined mainly by the temperature difference between the hot or cold object and duration of the exposure/contact. However, when considering exposure to volatile liquids (such as liquid nitrogen) the degree of tissue damage is also determined by the quantity of latent heat transferred, from the tissue to the liquid, as the liquid boils on contact with the skin. This latter transfer of energy becomes particularly relevant when excess tissue damage is caused inadvertently during certain cryosurgical techniques as our cases illustrate.

A wart is an abnormal growth of skin resulting from cutaneous infection with one of many types of human papillomavirus [2]. Despite the fact that the lesions are often self-limiting, in that the majority will eventually resolve over time, their unsightly appearance justifies treatment and patients often seek it. Several treatment modalities exist, the principle methods being cryotherapy and topical salicylic acid [3, 4]. The British Association of Dermatologists' guidelines list cryotherapy as the only treatment with A1 evidence to support its use in the management of cutaneous warts [4]. Other more recent systematic reviews of the management of cutaneous warts viewed cryotherapy less favorably [3,5]. Nonetheless, cryotherapy remains a popular and well recognized method of treating minor skin complaints such as warts and skin tags [6, 7].

Cryotherapy (or cryosurgery) involves the application of cold to achieve health promoting effects and its use in the treatment of benign skin conditions dates back to the end of the 19th Century [7]. In this paper the words cryosurgery and cryotherapy are used interchangeably. More correctly, cryosurgery refers specifically to the use of freezing to destroy or excise tissue. Whereas cryotherapy is used more generally to describe the use of cold for therapeutic effect, the application of "cold" may be localized freezing as with cryosurgery or more generalized cooling of the body. The application has been extended to the treatment of solitary solid malignant tumors (e.g., within the liver and prostate) as well as malignant lesions of the skin [7, 8, 9]. The technique has many advantages in that it is minimally invasive, low cost, and (when used correctly) can produce less scarring and pain compared to alternative treatment strategies [10]. Nevertheless, localized application of the coolant can be imprecise, resulting in excess freeze damage to surrounding healthy tissue [10, 11]. Other complications include pain and occasionally damage to digital nerves when treating cutaneous finger lesions [10].

The mechanism of tissue destruction and hence clinical benefit in cryosurgery is probably multi-factorial [7]. Ice formation is directly damaging to cells both to their membrane and internal cellular machinery such as mitochondria. Cells are also damaged by changes in the osmotic gradient across their cell wall, as well as by the disruption of their vascular supply resulting from the freezing process. Some of these effects are more pronounced after a rapid freeze, slow thaw, and then refreeze, which may explain why repeat freeze-thaw cycles in cryotherapy treatment of warts can achieve improved clearance of some lesions [7, 10]. A final contributory mechanism of action is thought to be immunological, given that local treatment can sometimes lead to resolution of lesions at a distant site [7].

In recent years, a cryotherapy device has been made commercially available for purchase without a prescription at many shops throughout the United Kingdom for the treatment of cutaneous warts and verrucae. The device works by loading a sponge tip with a cooling agent and then directly applying this tip to the lesion. We report 3 cases of children sustaining cold burns when using this device to treat cutaneous viral warts. All 3 cases presented to our department during the latter half of the year 2006.

Case Reports

Case 1

A 6-year-old boy had a wart near the tip of his right thumb. The warty lesion had been present for several months and was resistant to attempts to clear it using salicylic acid (Salactol®). Using the cryotherapy device his mother held the coolant device over the wart for approximately 20 seconds, spraying the volatile liquid over the thumb tip. A large painful blister soon developed over the tip of the boy's thumb. The wound was dressed with Mepitel and gauze, leaving the blister intact. Following 2 visits to the dressing clinic, the wound healed satisfactorily within 2 weeks and without the need for further follow-up. Despite the amount of local tissue damage the wart unfortunately recurred and the boy was discharged back to the care of his general practitioner for further care.

Case 2

An 11-year-old girl had a wart close to the third web space on the dorsum of her foot. She presented to hospital in August 2006, after her father had held the sponge bulb of the device to the lesion whilst dispensing the coolant. This resulted in tissue damage across the second, third and fourth web-spaces dorsally (Fig. 1). A deeper central area of tissue damage approximately 3 x 1.5 cm took longer to heal and also raised some concern about the potential for scar contracture that could lead to restricted movement of the toes. The burn healed completely after nearly four weeks but required twice weekly visits to our dressing clinic during that time. She was booked for a 6-month follow-up appointment at the scar management clinic. Fortunately, significant scar contracture did not result.

Figure 1	Figure 2a
Figure 1. Dorsal aspect of foot. The deeper areas of the burn can be seen centrally, close to the site of the original wart. Figure 2a. Dorsal aspect of hand, showing the initial appearance of burn at presentation to hospital.

Case 3

The third case also presented during August 2006. An 11-year-old boy had a wart on the dorsal aspect of his right hand between the second and third web-spaces. In this instance the patient's elder brother applied and activated the coolant device for approximately 20 seconds. The coolant spray dispersed across the boy's hand, through the web-spaces and onto the volar aspect of his hand. This resulted in partial thickness burns to both the dorsal and volar skin surfaces (Fig. 2). At presentation to the hospital he was unable to move his fingers due to the pain. His hand became progressively more swollen with small blisters developing over the burnt area (Fig. 2a). The wound healed satisfactorily and the boy was discharged from the dressing clinic after three weeks and given an appointment to attend the scar management clinic in 6 months. Again, fortunately significant scar contracture did not result.

Figure 2b	Figure 2c
Figure 2b. Appearance 5 days later. The small nodule centrally represents the site of the original wart. Figure 2c. Volar view of hand at first dressing change 5 days after injury.

Discussion

The mechanism of injury in each of the cases outlined above was essentially the same, with the device being activated whilst in direct contact with the skin, spraying volatile coolant over the skin surface. This resulted in tissue injury spreading radially from the site of application. Although each of the burns were managed conservatively, all required regular dressing changes at our dressing clinic for a period of time ranging from 2 to 4 weeks. It should be noted that the product in question does instruct the user not to spray the device directly onto the skin and warns of the possibility of causing unwanted tissue damage. This warning is written plainly on the packaging of the product and the injuries described resulted from a failure to follow the instructions correctly. Given that 3 cases presented to our department over a relatively short period of time, it is our belief that the instruction leaflet is inadequate in highlighting the potential complication of non-specific cold burn to normal tissue. Moreover, the design of the dispenser is such that inadvertent misuse of the product is not entirely surprising. This can be appreciated when one considers the different devices and methods used in cryosurgery in medical practice [6, 7]. The 3 commonly used methods are: the use of a directed applicator (i.e., a cotton bud that has been dipped in liquid nitrogen applied directly to the skin), a highly directional spray device or the use of a cryoprobe (Fig. 3).

Figure 3
Figure 3. Cryosurgery devices: Cotton-tip applicator (left); Liquid nitrogen spray (centre); and Cryoprobe (right). Reproduced from [6] American Family Physician 2004; 69(10):2365-72, with permission.

During the treatment of benign skin lesions it is recommended to cause freezing of tissue approximately 1-2mm beyond the lesion's visible margin, and preferably delineate the total field to be treated prior to commencing treatment [7, 10]. The cotton bud application technique is only suitable for relatively small, superficial skin lesions, given that it will not achieve substantial tissue freezing below a depth of approximately 3mm [7]. After dipping in an appropriate coolant agent such as liquid nitrogen, the bud is held in contact with the lesion to be treated until a narrow halo of visible ice forms around the bud on the surface of the skin - so as to achieve freezing of tissue 1-2mm beyond the lesion's visible margin. When using a professional spray technique, the spray tip is held approximately 1 cm from the surface of the lesion and sprayed for between 5 and 30 seconds depending on the size of the lesion being treated [7]. Such professional spray devices are very predictable in their direction and field of application. When used incorrectly, the commercial device used by the patients' relatives in our cases did not permit contained application of coolant, resulting in non-specific tissue damage.

Damage to healthy tissue (i.e., cold burn to surrounding skin) is an inevitable outcome of cryosurgery. However, there is clearly the potential complication of causing excess damage beyond what is desirable, as illustrated in the above cases and reported previously [11, 12]. The clinical application of cryosurgery has largely been a trained professional's realm of practice and devices available to the public over-the-counter are a relatively new phenomenon. Superficial cold burns resulting from failure to use a similar over-the-counter product correctly have recently been reported [12]. The problem with the design of these devices is that they employ a combination of two possible methods of application in their use (again Fig. 3). A "spray" maneuver is required to load the sponge tip with coolant, whilst the tip is directed away from the patient. This is then followed by direct application of the sponge tip to the lesion, without spraying. Although these steps are detailed in the instructional leaflet, they are obviously confusing to some individuals.

The ECRI (Emergency Care Research Institute) has provided some insight into the causes and treatment of burns within the health care setting [13]. They outline the vast array of devices that can be implicated in causing superficial skin injury and highlight the importance of thorough investigation when injury to a patient has occurred to help reduce the risk of a similar incident recurring. In a similar vein, we hope these cases demonstrate the need to review the various aspects of the use of commercially available cryotherapy devices and that this leads to a reduced risk of frostbite injuries occurring from their use in the future.

Conclusion

Cryotherapy is a well-established method in the treatment of viral warts and remains so, although further clarification of its clinical benefit is warranted [5]. When used by health care workers experienced in the use of such techniques, it should not result in significant damage to healthy tissue and any excess damage that does occur would usually be of minor consequence.

If cryosurgical devices are to remain commercially available, then we feel further safe-guards should be put in place to reduce the risk of future cases of burns resulting from their incorrect use. These safe-guards could include clearer warnings and instructions, as well as possibly a new design of the device itself. The warnings should highlight more clearly the possibility of causing unwanted damage to healthy skin (i.e., frostbite) and this in itself may result in users paying closer attention to instructions given. An alternative strategy to help reduce the risk of such injuries would be by placing some of the onus on pharmacists and shop-keepers who sell the product to warn customers as the product is bought over the counter and make sure they understand the correct method of application at this stage. Ultimately, the safest way for cryotherapy to be utilised is by health care professionals adequately trained in the use of such techniques and devices.

References

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