The Toenail “Abscess” in Elephants: Treatment Options Including Cryotherapy and Pathologic Similarities with Equine Proliferative Pododermatitis (Canker)
Abstract
Foot problems potentially represent the single most important clinical disease of captive elephants.3 Predisposing factors include obesity, lack of exercise, nail or sole overgrowth, improper foot care, poor hygiene, inappropriate enclosure surfaces, poor conformation, malnutrition, and secondary skeletal disorders such as degenerative joint disease.3,13,14 Furthermore, factors such as elephant management philosophy, disposition of elephants, facilities, and competency of staff in caring for elephant feet will contribute significantly to the foot health of captive animals.13 It is important to note that these conditions are rarely reported in free-ranging elephants.6
The elephant toenail abscess is characterized grossly by proliferative outgrowth of “crab-meat-like” tissue that may acutely rupture through the surface of the nail wall and/or adjacent cuticle or sole. True abscess formation with localized collections of suppurative material is not a consistent clinical feature. In most cases, the inciting cause of these lesions is typically not found and is likely due to one or more of the predisposing factors listed above. Once established, these frustrating lesions require extensive, intensive, and prolonged medical attention. If not cared for properly, these wounds may progress to phalangeal osteomyelitis and the need for surgical intervention.1,2,4,5 Sole abscesses are equally frustrating and difficult to manage with proposed etiologies similar to toenail lesions.8,17
There are no reports in the literature describing the pathology of the classic proliferative abscess tissue of the elephant nail abscess. Although variously interpreted as fibrous or granulation tissue, the authors are unaware of previous histologic descriptions of this tissue. Biopsy samples of toenail abscess tissue from two Asian elephants (Elephas maximus) at the San Diego Wild Animal Park (SDWAP) consisted of stratified squamous epithelium arranged in columns resembling horn tubules. The predominant histologic finding was marked, near diffuse, hydropic degeneration of keratinocytes. There were multifocal areas of suppurative inflammation with admixed bacterial colonies. Inflammatory foci comprised only a small portion of the lesion and were interpreted as the external surfaces of the biopsy with likely secondary bacterial colonization. Because descriptions of the normal histology of the elephant toenail could not be located, a grossly normal toenail from a different Asian elephant was obtained to compare histologic features with those of the toenail abscesses. Sections demonstrated formation of the toenail in a manner similar to that of the hoof of the horse and cattle with tubular, intertubular, and laminar horn. Primary and secondary epidermal laminae were identified.
Proliferative lesions of horn-producing epithelium associated with ballooning degeneration and inadequate keratinization of keratinocytes, have been described in horses as equine “canker” and coronary band dystrophy.9,19 Equine canker is most commonly observed in the hind feet of draft horses and begins in the frog, sometimes with extension to the sole and hoof wall. Grossly, lesions are characterized by soft, white papillary to “cauliflower-like” tissue associated with a foul odor. Similar to what is noted in elephant foot problems, predisposing factors for the development of equine canker include poor hygiene or wet environmental conditions.
There is a lack of gross and histologic description of the normal nail and sole tissue of the elephant12 and further investigations are warranted. A review of the anatomy and histology of the normal equine hoof15 may provide a basic understanding of the elephant nail until more specific and detailed elephant information is available. From our investigation, the authors offer that a more accurate description of the elephant toenail abscess would be proliferative pododermatitis, the term synonymous with equine canker. A more colloquial term such as “elephant canker” may be appropriate, as well.
Canker in the horse is an uncommon but difficult to treat disease of the hoof.16,18,19 Historically, treatment options for elephant toenail abscesses include corrective trimming, superficial debridement, and application of topical disinfectants or antibiotics.2 Others have constructed innovative sandals to treat and protect the affected sole or nail with success.8 The use of regional intravenous perfusion of the affected limb with antibiotics has also been successful.11 Since the elephant nail abscess now appears to be histologically and clinically comparable to equine canker, this novel characterization of an old disease may offer unique insight for treatment. In the least, it has provided our practice with a new list of treatment options and experienced equine clinicians for consultation who have been managing patients with a similar disease for many years.
One of the Asian elephants at the SDWAP has had chronic toenail abscesses for over two years. Radiographs of the affected digits (as reported by others to assess degree of involvement)7 have, fortunately, been negative for evidence of osteomyelitis. Several bacterial and fungal cultures of deep tissue biopsies and swabs of affected lesions have resulted in a mixture of organisms with no consistent single etiologic agent. Biopsies were found negative for presence of viral DNA (elephant papillomavirus and herpesvirus) by PCR. Typical elephant foot care at the SDWAP includes trimming and debriding with hoof knives, foot soaks, and topical antibiotics. Although difficult, attempts are made at keeping the affected foot clean and dry. Following recommendations for the treatment of equine canker,10 we recently implemented the routine use of cryotherapy in all elephants with proliferative pododermatitis with improved success in the control and recession of exuberant nail lesions.
The proliferative tissue of the nail is first cleaned, then disinfected, debrided, trimmed with hoof knives, and allowed to dry. Modified brass branding tools with contact surfaces of variable size (2–5 cm diameter) and shape (round or ovoid) are placed into liquid nitrogen (-196°C) for several minutes and then placed directly on the cankerous tissue for 30–60 seconds. This process is then repeated 4–5 minutes later, following a complete thaw of tissue. Within 24 hours, the cryo-burned tissue becomes macerated and necrotic and is readily removed with gentle scrubbing. Cryotherapy offers the advantage of destroying tissue to a deeper level than trimming alone and provides hemostasis as well. Because of decreased sensation at the cryotherapy treatment site, a memorable painful event is avoided, and the elephant patient is more routinely accepting of this technique. With the use of hoof knives, we typically remove 2–3 mm of proliferative tissue before the patient refuses further treatment, presumably due to discomfort. With cryotherapy, we are able to remove an additional 3–5 mm of tissue by cell freezing and necrosis. The result is quicker resolution of cankerous lesions without the need for aggressive, and potentially painful, interventions.
In conclusion, it appears that elephant nail abscesses can best be described as proliferative pododermatitis, or canker, as is seen in other species. Further gross and microscopic descriptions of normal and pathologic nail or sole lesions are necessary. Routine cryotherapy has shown promise in the treatment of these chronic, frustrating, and potentially devastating lesions of our captive elephants.
Acknowledgments
The authors would like to thank our colleagues of the Department of Veterinary Services at the San Diego Wild Animal Park; Department of Pathology, Zoological Society of San Diego; equine veterinary consultant, Dr. Lynn Richardson; and Jeff Andrews and his elephant care staff at the San Diego Wild Animal Park.
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