Alternate Applications of Living Skin Equivalent

Introduction Living skin equivalent (LSE)*, or tissue-engineered skin, is a bilaminar structure of epithelium cultured upon a dermal equivalent. Clinically, it has characteristics that closely resemble a skin graft. As such, it is used in the capacity of a prefabricated skin graft. LSE is currently approved by the FDA for chronic wounds, specifically certain diabetic foot ulcers (DFU) and venous stasis ulcers (VSU).1–3 As clinical experience broadens with LSE, physicians across the country are reporting its use in the treatment of other, “off-label” wounds beyond those approved by the FDA, such as acute excisional wounds4,5 (including Mohs surgery), epidermolysis bullosa,6 and other dermatologic conditions, such as ulcerative sarcoidosis,7 necrobiosis lipoidica,8 and pyoderma gangrenosum.9 Most of these reports have been case reports or small series. The authors have experienced a broadening of indications for LSE within their own practice and have found LSE particularly useful in avulsion injuries and certain salvage situations (those situations where an autologous graft or flap has experienced necrosis). However, learning how to properly select wounds for management with tissue engineered skin and learning proper post-application dressing management are processes acquired with time and experience. Materials and Methods The medical records of 58 patients treated with 84 separate LSE grafts were reviewed retrospectively. This represents a three-year experience with LSE (January 1999 through July 2001). Living skin equivalent is a bilaminar skin equivalent produced by seeding a type I bovine collagen matrix with human fibroblasts. Upon this, human keratinocytes are then cultured and allowed to stratify and cornify. The result is a bilayered living tissue with dermis and epithelial components. Of the 58 patients treated, 41 were treated for indications other than venous stasis disease or diabetic foot ulcer. These are “off-label” applications and make up the study population. Seventy-seven percent of our applications were for alternate applications; whereas, 23 percent were for VSU or DFU. The etiology of each wound treated is as follows (Figure 1): • 30-percent traumatic • 23-percent salvage • 21-percent venous stasis ulcer (VSU) • 8-percent burn • 7-percent iatrogenic • 5-percent pressure ulcer • 4-percent other • 2-percent diabetic foot ulcer (DFU). The location of application within the alternate-use subset was as follows (Figure 2): • 56-percent lower extremity • 27-percent trunk • 15-percent upper extremity • 2-percent head and neck. Within the alternate application group, the age range of patients was 19 years to 92 years. Of these patients, 54 percent had two or more significant systemic comorbidities. In fact, 22 percent were chronic systemic steroid users, 24 percent had diabetes, and 27 percent were active smokers. Eighty-six percent of these wounds had failed a physician-supervised, conservative regimen of wound care. The average wound age at the time of LSE treatment was 94 days. Results Seventy-eight percent of all wounds in the alternate application group healed completely. Twelve percent of wounds healed by at least 50 percent (partial wound healing) and ten percent exhibited minimal (Traumatic wounds (n = 17). The authors experienced a complete healing rate of 94 percent and a partial healing rate (at least 50% improvement) of six percent with no failures of healing in wounds of traumatic origin treated with LSE. This group of wounds included mechanisms, such as avulsion and crush injuries. One of the issues of using LSE in wounds of traumatic origin has been the concern that treatment with LSE may lead to an increased wound infection rate. In this study, there were no instances of wound infection in this population, even in those patients treated within the first few days after injury. In this respect, LSE clinically behaves as any other biologic dressing or graft. However, LSE may actually have an advantage with respect to antimicrobial activity when compared to nonliving constructs or grafts. LSE has been found to express high levels of human beta 2 defensin, a natural antimicrobial agent expressed by epithelial cells.10,11 Certainly, the acute use of LSE should be avoided in heavily contaminated wounds. These wounds should be converted to stable, subacute or granulated wounds before grafting. In clean wounds, the presence of granulation is not a necessary prerequisite for treatment with LSE. Within the series of trauma patients, the authors identified a subset of nine patients with dermal atrophy who had avulsion lacerations. The diagnosis of dermal atrophy was made clinically. All patients within this subset had dermal atrophy on the basis of age (all were over 65 years of age) and/or the use of chronic systemic steroids. In short, these patients were the typical “onion-skinned,” often institutionalized, elderly that present with avulsions out of proportion to the low-energy mechanism of wounding (a fall from a wheelchair, etc). Two thirds of these patients had two or more comorbidities and one third were oxygen dependent. All of these patients healed completely with LSE treatment (Figure 4). Average time to healing in this particular subset was 8.8 weeks. The healing was durable with no recurrences at an average follow up of 19 months (range 5–34 months). This subset of patients showed us that LSE can be used within the first 24 to 48 hours of clean avulsion injuries. In this population with a high incidence of comorbidities, anesthetic issues are avoided because treatment with LSE requires only topical or local anesthetic and often none at all. In addition, donor site morbidity is avoided because no donor site is created. Because LSE treatment can be used on an outpatient basis, the hazards of inpatient treatment (DVT, hospital-acquired infection, etc.) are avoided. Nursing home acuity is not increased, as we performed all of the dressing changes on a weekly basis in the outpatient clinic (Figure 5). Nursing home staff, therefore, are not burdened by intricate wound care, and transfer to higher acuity residences is avoided. The authors highly recommend LSE treatment for the dermal atrophy or elderly patient with an avulsion. Burns (n = 4). Reports of the use of LSE in burn wounds are limited; the first case was formally reported in January 2001.12,13 This study had a small patient population within the burn category but had excellent results. All patients had full-thickness burns except one who had deep partial-thickness burns. All of the patients healed the LSE-treated burn completely. The average time to healing in this group was 4.5 weeks. Significantly, none of the burn wounds exhibited appreciable contracture after treatment. It would therefore seem that adequate dermal replacement does occur after treatment with LSE (Figure 6). A formal histologic inquiry into this matter should be performed. The study found particularly useful the application of LSE for “touch-up” grafting on areas of failed autologous graft that had sheared. This can be done right in the intensive care unit bed without having to return an unstable patient to the operating room. One advantage of LSE over biologic dressings (such as xenografts, homografts, etc.) is that the need for further grafting (even thin epidermal grafting) is avoided because the product is a complete bilaminar equivalent. The study also found that the graft can survive mild-to-moderate pseudomonas colonization if the dressings are changed in a timely fashion, often using acetic acid without affecting the graft. The authors typically used no topical antimicrobial agents on the initial grafts and still do not. Many clinicians, however, recommend topical antimicrobials including silver-impregnated gauze. In both the burn patients and the dermal atrophy (steroid-dependent) patients discussed, four instances of primary vascularization and graft take occurred (Figures 4c and 5c). Whether LSE heals by this method, by supplying growth factors, or by some other mechanism involving the nebulous concept of altering the wound “milieu” has been controversial. Because the four patients with clear, clinical primary take occurred in either burn patients or steroid-dependent patients, it is interesting to postulate that the immune suppression that occurs in this class of patients may have led to primary take and faster healing (4.5 weeks vs. 10.3 weeks on the average). The level of immunogenicity of LSE is unknown, but LSE does not clinically undergo rejection like an allograft. Fertile areas of application may be in deep partial-thickness burns in which the LSE may act as both a biologic dressing, preventing desiccation and conversion to full-thickness injury, while simultaneously providing the scaffold for complete healing. In this respect, it is interesting to speculate on its role in protecting pigmentation. Lastly, it could be an excellent dressing for donor sites on pediatric patients, preventing postoperative pain. Salvage (n = 13). We found LSE to be particularly useful for salvaging failed autologous grafts or flaps. Seventy-five percent of these patients completely healed their wounds, while 25 percent had minimal healing. The latter patients either required further autologous grafting or went on to heal by secondary intention. Examples of salvage cases were, among others, failure of autologous grafts (over a free-flap pedicle, after melanoma wide excision, in a contaminated abdominal donor site [Figure 7], etc.), necrosis at the T-intersection of three breast reductions (Figure 8), failed local flaps (toe filet flap), etc. LSE provided stable healing in the patients who had already healed one set of painful donor sites associated with a failed primary autologous graft. These sensitized patients were understandably reticent about the prospect of healing a second donor site. One patient with fibromyalgia strictly forbade us to attempt further autologous grafts. Based on her experience with effective, painless LSE treatment, the authors recommend LSE in patients with reflex sympathetic dystrophy (RSD) or pain syndromes in which creating a donor site risks significant pain. Within the overall experience of 41 alternate use patients, 15 percent had a history of previous autologous grafting. Sixty-three percent of these healed completely with LSE. A failed autologous graft is not a contraindication to treatment with LSE and, in consideration of the above issues, may even be an indication for LSE. Iatrogenic wounds (n = 4). These wounds resemble salvage cases, both in etiology (previous surgery) and chronicity (application of LSE is used as a secondary closure). Most (75%) were dehisced abdominal wounds. These are wounds with high motion and are difficult to dress, particularly in the obese. Fifty percent were healed with LSE, while 25 percent improved (50% healed). Treatment failure was associated with shearing. On this basis, the authors recommend anchoring the LSE and considering the adjunctive use of fibrin glue. Like the salvage cases, many of these patients had a prolonged and difficult hospital stay and were reticent to have another surgical procedure, such as autologous grafting. LSE provided an easy, painless alternative. Other considerations. The authors have successfully used LSE on patients with certain systemic and cutaneous conditions. We have treated patients with systemic lupus erythematosus, Sjogren’s syndrome, and pyoderma gangrenosum. The treatment of a patient with long-standing refractory bilateral leg ulcers due to necrobiosis lipoidica diabeticorum was less successful. In this patient, the open wounds that were treated healed, but new marginal ulcers appeared at the edges of the LSE (Figure 9). The authors have successfully treated a patient who had an autologous stem cell transplant incurring no sign of graft-versus-host disease. The least successful group was a small group treated for pressure ulcers. One of three healed, and this was a paraplegic foot ulcer. The failures were trunk wounds. Failure to heal was directly related to shearing and inadequate pressure relief. Wound management after grafting with LSE is an important issue. The appearance of LSE after grafting is often different from what we have come to expect in autografts that have taken primarily. LSE usually undergoes a yellow, gelatinous hydrated phase, which may appear like moist eschar or even be misinterpreted as pus or fibrinous exudate. The clinician must avoid the temptation to deem the graft a failure and therefore debride it. It should not be washed or manipulated. The authors often leave a nonadherent layer against the graft undisturbed for one or two weeks initially, then wait four to six weeks before judging the quality of healing. The authors use a layered dressing with compression on the extremities. They often resort to fibrin glue, suture, or staple anchoring on the mobile or shear-prone trunk. Dressings are often changed on a weekly outpatient timetable, thus simplifying management of the elderly or institutionalized. Lastly, the clinician should be aware that Medicare and many insurance plans will not cover these off-label uses. When possible, pre-approval by third-party payers should be sought before application, particularly when used in an outpatient setting. The product is an expensive modality, and no cost analyses have been published to date comparing LSE to other methods of treatment in a controlled trial. Summary LSE is an effective tool for wound healing across a broad range of alternate applications, i.e. those other than venous stasis ulcer or diabetic foot ulcer. Healing has been clinically durable. When application is chosen appropriately, LSE can provide a painless and convenient alternative to autologous grafting, particularly in the elderly, the patient with pain syndromes, those who have iatrogenic wounds, and those who have failed attempts at wound closure. *Apligraf®, Novartis Pharmaceutical Inc., East Hanover, New Jersey