By John Lewis, VMD, FAVD, DAVDC
I’ve got another “dental zebra” for you. For those unacquainted with my dental zebra series, I am not referring to the striped horse but rather the rare diagnosis that is sometimes referred to as a “zebra” diagnosis.
Theodore Woodward, medical doctor and researcher at the University of Maryland, is credited with creating this term to describe the rare diagnosis. He taught his interns when trying to make a diagnosis: “When you hear hoof beats behind you, don’t expect to see a zebra.” In Maryland, this is good advice, as hoof beats are more likely to be from horses rather than zebras.
A more common disease is more likely to be presented to you than a rare one. However, zebras can sometimes be found in unusual places (Figure 1). Therefore, when I had the opportunity to teach students, interns and residents at the University of Pennsylvania, I instructed them to be on the ready for both horses and zebras.
This zebra runs red
I haven’t discussed this zebra in my column before, but I often spread the word about this condition when I lecture at various conferences, and I recently saw a case that reminded me to share it. This particular case had been going on for 18 months without an explanation for its etiology. If you diagnose one case of this disease, you will never forget it on your list of differentials for oral bleeding.
As soon as I heard the signalment and history of the case, I guessed what the diagnosis would be even before I saw the patient. I’ve come to learn that having preconceived diagnoses in patients you haven’t seen yet is not necessarily a good thing, but it’s always good to have past experiences in your memory bank.
Tyson is an 8-year-old male neutered boxer who presented with a history of oral bleeding, which had been intermittent for the past 18 months. A few episodes of bleeding were so profuse that blood had soaked a hand towel. Conscious oral examination generally had been unfruitful in the past. A previous anesthetized oral exam at an emergency center six months previous showed an ulcerated area on the ventral surface of the tongue. This area was biopsied with a diagnosis of locally extensive, fibrinosuppurative to ulcerative glossitis. The ulcerated area was sutured closed. Bleeding episodes continued, occurring almost every mealtime.
Recent blood work (CBC/chemistry screen) was unremarkable; PCV, PT and PTT done during my examination were normal.
Tyson was somewhat reluctant for a complete conscious oral examination, so we placed him under anesthesia to assess the oral cavity more closely. Oral examination revealed moderate plaque and calculus, and generalized gingival enlargement in the absence of gingival ulceration.
The most significant finding was ulceration under the tongue that showed a chronic-active process, as evidenced by fibrous tissue around the periphery of the ulcerated area (Figure 2). Touching the ulcerated areas with a probe resulted in bleeding. Upon pulling the tongue toward the front of the mouth, the ulcerated areas lined up with three very sharp mandibular incisor teeth (teeth 301, 302, 401) that had been worn to a chisel point (Figure 3). The ulcerated areas were debrided; edges were freshened and closed with 5-0 poliglecaprone on a tapered needle .
The (hoof) beats go on
I’ve seen this problem in multiple large-breed dogs, including great Danes and Labradors, but mostly I’ve seen it in boxers. My first case was a boxer that Sarah Bonner, DVM, Dipl. AVDC, and I saw at Penn during her residency with a similar history to Tyson’s.
Over the past three years at NorthStar VETS, I have seen approximately two to three cases per year. It seems the characteristics necessary for chronic self-trauma to the ventral surface of the tongue include worn incisors and a long, heavy tongue that regularly hangs down over the incisors.
Boxers are most likely to have these two characteristics. Born with an amazingly long, wide and heavy tongue, all they need is wear of the mandibular incisors to a chisel point. Every time the tongue hangs out of the mouth, chronic irritation from the sharp incisors causes ulceration of the mucosa and potential trauma to the many superficial veins of the ventral tongue. Therefore, even visually unimpressive lesions can bleed quite a bit. Lesions may be linear and difficult to see upon conscious exam.
Wear of the incisors can occur from abrasion or attrition. Abrasion describes tooth wear due to chewing on something, be it hard toys or the patient’s own fur due to allergies. Attrition refers to tooth wear due to tooth-to-tooth contact, which is likely when malocclusions occur.
Tyson’s case was similar to others I’ve treated, and surgical closure of the tongue defects and extraction of the sharp teeth proved curative. Odontoplasty (subtle shaping of the tooth with a water-cooled white stone on a high-speed handpiece) also might have been effective, but I didn’t take any chances of recurrence and extracted the sharp teeth.
Keep this zebra in mind when blood flows from a boxer’s (or other large-breed dog’s) mouth!
Dr. John Lewis practices veterinary dentistry and oral surgery at NorthStar VETS in Robbinsville, N.J.