Virginia Therapeutic Farriery

An Overview OfEquine Canker

Reprinted with permission from the American Farriers Journal.
Originally printed in The American Farriers Journal, 2018 Volume 44 # 7

Stephen E. O'Grady DVM, MRCVS

Equine canker is a disease in searchof a definition since the causehas not been determined. It couldbe described as a pathological responseto an insult to the foot’s horn-producing tissues. Equine canker has beendefined as an infectious process thatresults in the development of a chronic,hypertrophic, moist pododermatitis of the hornproducing tissues, generally in the palmar/ plantar sections of the foot. Usually originating in the frog, canker may remain focalor invade the adjacent sole, bars and hoofwall. Canker is generally confined to andproliferates from the epidermal tissue andrarely invades the underlying dermal tissue.Although the etiology of canker remainselusive, it can consistently and effectivelybe treated and resolved.1,2,3,4

Etiology Of Canker
The etiology of canker remains evasive, but generally is seen in a frog that isunhealthy and enters through a break in thehorn tissue. There is another disease entitytermed “coronary band dystrophy,” whichappears to have an immune-mediated component that is associated with or can leadto canker (O’Grady SE. “Coronary BandDystrophy,” 2017, in review). Wet environmental factors may play a role as thereis a seasonal incidence of canker duringthe rainy season in Florida from July untilDecember.1

Previously, it was felt that unhygienicconditions were causative, but cankeris seen in horses that are well cared forand receive regular hoof care. At onetime, canker was commonly seen in draftbreeds, but now is diagnosed in all breeds,especially Thoroughbred and warmbloodhorses. It can occur in one or multiple feet,affect one or multiple horses on a givenfarm and has no predilection to the age orsex of the horse.

Figure 1: A foot with chronic thrush. Note the unhealthy nature of the frog and the loss of structural mass.
Figure 2: Early canker in the center ofthe frog. Note the light brown epithelial tissue that is trying to surroundthe ulcerated lesion.

Clinical Signs Of Canker
Canker generally originates in the frogand can be mistaken for thrush in the earlystages. Thrush is limited to the frog andresults in a very recognizable deteriorationor loss of frog tissue where on the otherhand there is a proliferation of tissue withcanker (Figure 1).

Canker may present anywhere from afocal area of granulation tissue in the frogthat bleeds easily when abraded to longfilamentous fronds of hypertrophic horn.Canker is characterized by numerous smallfinger-like papillae consisting of a soft,off-white material that resembles a “cauliflower-like’ appearance and is coveredwith a caseous white exudate that resembles cottage cheese (Figures 2 and 3a-3c).

Figures 3A, 3B & 3C: Figure 3A (left) shows filamentous fronds of hypertrophic horn. Figure 3B (center) showsthe finger like papillae that presents a “cauliflower” appearance. Figure 3C (right) shows a white caseous exudatethat resembles “cottage cheese” beneath the outer hard layer of the frog. The condition is frequently, but notalways, accompanied by a foul odor.

The condition is frequently, but notalways, accompanied by a foul odor.However, if any type of antiseptic or causticmedication has been used for treatment, thesmell will disappear. The affected tissuewill bleed easily when abraded and maybe extremely painful to the horse whentouched or pressure is applied. Varyingdegrees of lameness will be presentdepending on the extent and depth of theinfection. Most horses are not lame if thedisease is recognized and treated early.

Figure 4: Photomicrograph on the left shows normal epidermis/dermis offrog. Photomicrograph on the right shows the tissue affected with canker.Red arrow is papillary hyperplasia, green arrow is keratolysis, yellow arrowis degeneration of the outer layer of the epidermis and blue arrow is a mixedpopulation of bacterial organisms.

Diagnosis Of Canker
A presumptive diagnosis of canker isbased on ruling out the presence of thrush,the gross appearance of the affected hornytissue covering the frog, a fetid odor andthe ease with which the abraded tissuebleeds. However, a definitive diagnosismay be confirmed with a biopsy. Biopsyis most useful in recurrent cases or whenthe lesions do not have the characteristicappearance or location in the foot.

Histologically, the lesion is read as a“chronic hypertrophic moist pododermatitis.” It is characterized by a proliferativepapillary hyperplasia of the epidermiswith dyskeratosis, keratolysis and ballooning degeneration of the outer layersof the epidermis. A mixed populationof bacterial organisms are observed inthe stratum germinativum layer of theepidermis of the frog (Figure 4). Culturesper se are unrewarding as they typicallyproduce an assortment of environmentalorganisms such as “Bacteroides sp.” and“Fusobacterium necrophorum,” the usualopportunistic bacteria found in the solarsurface of the horse’s foot.

Figure 5: No canker present in thefrog, but note how the foot should beprepared prior to debridement. Notethe slope of the bars for exposure offrog sulci.

Treatment Of Canker
Treatment of canker is a realisticexample of a joint venture between a veterinarian and a farrier. From a legal andethical standpoint, working with dermaltissue is the practice of veterinary medicine. The effective veterinary treatment ofcanker requires sedation, local anesthesia,surgery (debridement without hemorrhage)and medication. Many veterinarians arenot familiar with farrier tools or their use,unable to trim and prepare the foot priorto debridement, are unable to explore thehoof capsule appropriately and are unableto provide the necessary follow-up farrierycare. This describes the farrier’s role andinput. Treatment should be considered ateam approach with the veterinarian, farrier and owner/caregiver

Trimming and preparation of foot. Animportant aspect that is often overlookedis to trim the foot prior to surgery. Try toaddress any hoof capsule distortion at theonset in order to give the foot a mechanical advantage. All loose exfoliating soleis removed from the solar surface of thefoot. The bars and sole of the hoof capsuleadjacent to the frog are explored to be surethe horn in this area is not involved. Allunderrun or loose horn is removed downto solid structures (Figure 5).

Figure 6: Esmark bandage in place.

The heels are trimmed such that the hoofwall at the heels and the frog are on thesame plane or approach the same plane.The frog should not be recessed betweenthe heels of the hoof wall at the beginningof treatment or the affected tissue will notheal. I also trim the bars on more of a slopethan usual because I want good exposureto the sulci around the frog. After the footis prepared with the appropriate farriery,soaking the foot with any of the variouscleaning solutions or products is unnecessary. The foot is now placed in a bucketof clean water and the foot is scrubbedthoroughly with an antiseptic soap using afirm brush. I prefer to do the debridementstanding under local anesthesia but it canbe done under general anesthesia if thereare behavior issues with the horse or at thediscretion of the clinician.

Debridement. A tourniquet such as anEsmark bandage or a length of tire innertube cut at a 3-inch width is placed startingat mid-pastern to above the fetlock (Figure6). It is essential to create a bloodless fieldso the demarcation between normal anddiseased tissue can be seen during debridement. All abnormal tissue is removed untilthe tissue resembles a pink velvet color withnumerous pin-point hemorrhages, whichare the dermal papilla (Figure 7).

Remember that canker is generally limited to the epidermis, so debridement needsto be careful, gentle, thorough and widerather than aggressive, deep and radical,which often leads to unnecessary removalof the dermal tissue under the lesion. Thistissue is necessary for re-growth of healthyhorn and cornification. For debridement, Iuse a small pair of rongeurs to remove thebulk of diseased tissue, a sharp loop knifeand a #12 scalpel blade (Figure 8).

Figure 7: Frog surgically debrided.Papillae can be seen but any hemorrhage has been wiped off. Note thinstrips of healthy tissue left intact(red arrow).
Figure 8: Tools / instruments usedto facilitate debridement.

After the bulk of the diseased tissue isremoved, the remaining layers of diseasedtissue just peel off in strips with the loopknife and the blade is used in the tightermore obscure areas. The debridement isfollowed by cryotherapy to freeze the areathat has been debrided to remove residual bacteria from the surface in a doublefreeze-thaw, freeze-thaw pattern using acommercially available coolant spray.

Aftercare Of Canker
There are a variety of topical preparations that can be used followingdebridement but the astringents (dryingagents) may play the most important role.I use 4-inch x 4-inch gauze sponges moistened in a solution of 10% benzoyl peroxidein acetone, sprinkled with metronidazolepowder placed over the debrided site. Thereare other topical products available such asdry dressings that have been soaked in asolution of tricide/gentocin/lincomycin andan oxytetracycline/metronidazole paste thatmay be equally effective. No caustic preparations should ever be used as they willburn or damage the dermal tissue tryingto restore healthy horn.

The foot is then bandaged using anycombination of products — baby diapersattached with a cohesive bandage is a veryinexpensive option. A shoe with a treatment plate has become popular with cankercases, but I feel it is contraindicated as itneither keeps the foot as clean or as dryas necessary post debridement. Once thesurface has a complete layer of thin cornification, a treatment plate can be used ifdesired.

Client compliance. Owner compliancefor the aftercare is critical for a successfuloutcome. The bandage is changed dailyfor the first 7 to 10 days, and then at leastevery second day. At each bandage change,the affected area is cleaned gently with anantiseptic solution (not antiseptic soap),rinsed with free-flowing saline and driedwith a paper towel. The topical medicationof choice is applied and the foot is rebandaged. It is crucial to keep the animal in adry environment such as a small dry lot or astall bedded in saw dust or wood shavings

The owner should look for any focalor small reoccurrences of disease in thedebrided surface at each bandage change. Ifan area of abnormal growth is noted, theseare managed with light debridement using adry gauze sponge followed by cryotherapy.The foot should be fully cornified within3 to 6 weeks and a treatment plate can beapplied at that time if desired (Figure 9).

Figure 9: Before and after pictures of a canker case. After picture is 2 weeks post debridement.

Corticosteroids. There appears to be animmune-mediated component to canker asthe corticosteroids make a profound difference in the outcome of the case. I put allcases on a descending dose of oral prednisolone during the treatment phase of canker(generally 4 weeks).3,4

Discussion
I reported with Florida veterinarian JohnMadison on 60 horses with canker in 2004and then published an update on equinecanker with North Carolina State Universityvet Rich Redding in Veterinary Clinics ofNorth America —Equine Practice in 2012.I now have over 150 horses in the database.The treatment of equine canker has alwayspresented a dilemma for veterinarians andfarriers due to the historically poor prognosis. The etiology of canker remains obscure.However, the disease can be consistentlyand effectively treated. It does not appear tobe a disease of horses caused by poor care orunhygienic conditions. In the database, mostof the horses treated were well cared forand received routine hoof care. While thehind limbs seemed to be affected more frequently, forelimb involvement is common.

Trimming the foot, thorough debridementand owner commitment are important for asuccessful outcome of this condition. Carefuland thorough wide debridement of the lesionis essential, rather than aggressive radicaldebridement with the common connotation“cut it all out.” The dermis has to be sparedin order for healthy epidermis to be producedand cornified. Emphasis must be placed onkeeping the surgical wound clean and dryuntil the defect has completely cornified.Owner compliance to perform the dailyfootcare is always a critical and essentialelement in the treatment of equine canker.

REFERENCES
  1. Moyer, W.A., Colohan, P.T.: Canker. Equine Medicine & Surgery, 5th edition, Mosby, St. Louis (1999); 1544-1546.
  2. O’Grady SE., Madison JM. How to treat equine canker. Proceedings: Am Assoc Equine Pract 2004; 50:202-205
  3. Oosterlinck, M., Deneut, K., Dumoulin, M., Gasthuys, F. and Pille, F. Retrospective study of 30 horses with chronic proliferative pododermatitis (canker). Equine Vet Educ, 2011; 23:466-471.
  4. Redding R., O’Grady SE. Nonseptic Diseases Associated with the Hoof Complex. Vet Clin N Am Equine 2012; 28:2; 407-421.