Kodiak and the Recurring Keratoma
Published in modified form in "Equus"

Kodiak was a 14-year-old big bay thoroughbred gelding who carried Nan Rowe on high mountain trails and participated in a big game hunt or two. He arrived at our clinic with a history of intermittent lameness and a recurring abscess of the right front hoof. This had gone on for over a year with repeated treatment for the abscesses. The lameness had really cut into his trail time. Nan brought Kodiak to us for a second opinion.

The front wall of Kodiak’s hoof bulged ominously. When Dr. Jim Latham used hoof testers, he found a painful area on the sole directly beneath the bulge. We took x-rays. The films showed a wedge shaped, somewhat irregular defect in the third phalanx, the coffin bone where bone tissue had been destroyed. The lateral view showed the tissue destruction extended well up the bone.

Jim used an abaxial nerve block to desensitize the hoof and dug out a necrotic area on the sole involving the white line. He then flushed pus and blood from the area, soaked the hoof in diluted Betadyne (tamed iodine), and packed the defect with gauze and chlorhexidine disinfectant. Kodiak received phenylbutazone for pain.

The differential diagnosis included bone infection, a benign tumor known as a keratoma, malignant tumors like squamous cell carcinoma and melanoma, or an epidermal inclusion cyst. We needed to remove the mass and so we scheduled Kodiak for surgery.

A week later, the big bay horse was walking much better but was still lame. We admitted him to our clinic barn early in the morning, soaked his hoof in disinfectant and picked the sole clean.

We sedated Kodiak with detomidine and added butorphanol to ensure pain control, and Jim performed a low 4-point nerve block to desensitize the hoof during surgery. We applied a tourniquet to control bleeding.

Jim cut out a section of dorsal hoof wall with a Dremel tool, then carved out the underlying sole to increase exposure to a round mass. He dissected the mass from the underlying bone and surrounding laminar tissue. He scraped the bone with a scooping tool, a curette, and used rongeurs, sharp edged plier-like forceps, to clear margins back to healthy appearing tissue. The mass appeared fibrous and well defined when sectioned in half. The owners elected to forego biopsy at that time.

We packed Kodiak’s hoof with chlorhexidine-soaked gauze and wrapped it for protection. Jim prescribed twice daily trimethoprim/sulfa, antibiotics to guard against infection, and phenylbutazone was continued to control discomfort. By morning, Kodiak was walking comfortably and his bute was reduced to one gram twice daily. The packs and wraps were changed daily and in three days farrier Greg Wells applied an egg- bar shoe with a metal hospital plate. Kodiak went home and his owners removed the plate, soaked his foot and changed his disinfecting packs daily.

Two months later, on recheck, we noted a suspicious growth within the healing granulation tissue in the defect in Kodiak’s hoof. We were all discouraged but Jim and Kodiak’s determined caretaker made the decision to operate one more time. Using a similar protocol, Jim extended the hoof wall flap further up the hoof wall and again removed all suspicious tissue. Because of concerns about regrowth, he then injected the anti-cancer drug, 5-fluoro-uracil (5-FU) into the surrounding tissue to attack any microscopic remnants of the tumor. We hoped this more aggressive and somewhat novel treatment would halt the regrowth of the epithelial cells that produced the keratoma. Jim applied a metal band screwed into the hoof wall for additional support and again packed the surgery site.

A biopsy of the recurring mass showed keratinaceous material (sulfur containing proteins that make up hair, hoof or horn), inflammatory cells, secondary bacterial infection, and atypical proliferating squamous epithelial cells which represented a keratoma.

A keratoma is an uncommon, slow-growing tumor produced by the cells that produce the hoof wall. The growth may begin near the coronary band but can extend inside the hoof wall down to the sole and bulge along the white line. Direct trauma to the hoof wall, local irritation, or recurring abscesses may instigate a keratoma, and the tumor eventually puts pressure on the sensitive laminae and on the distal phalanx, causing pain and lameness.

We repeated the 5-FU injections three times at two week intervals, and the defect began to fill in with normal granulation tissue. The owner continued to soak and pack the hoof defect.

In two more months, Kodiak was walking well, and the hoof continued to granulate and heal. At three months, we were satisfied that the keratoma was gone and planned repair of the hoof wall defect. One week before Christmas and six months after surgery, the defect had grown down half the length of the hoof wall and Greg Wells packed it with Equithane. At the next shoeing, Greg applied an egg-bar shoe with clips and discarded the hospital plate. The defect was closed. It was a happy holiday for Kodiak, and he’d look forward to a full season in the high country of Colorado free of his keratoma and free of lameness.

5-Fluorouracil (5-FU) interferes with DNA and RNA synthesis Since DNA and RNA are essential for cell division and growth, 5-FU’s greatest effect is on cells that are growing and rapidly dividing, like tumor cells. 5-FU crème is used topically to treat equine sarcoids and squamous cell carcinomas (SCC) of the skin. An ophthalmic form of 5-FU is used to treat SCC of the eyelid or cornea. In injectable form, 5-FU is used to treat a variety of cancers. The drug is also used in humans and other animals.
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