Why do we love encountering zebra diagnoses? They are real-world tests that walk through our door at any given moment.
They add variety to the more frequently presenting conditions.
Accurate assessment of the zebra diagnosis allows us to utilize our years of training for the good of our patients.
A question for those of you who are veterinarians: When was the first time you heard of the disorder sublingual linear foreign bodies?
Was it when you worked in veterinary practice before veterinary school? Or was it during veterinary school? I vividly remember learning about sublingual linear foreign bodies in a second-year course of veterinary school.
The professor described this as a common occurrence when cats ingest a piece of string or thread, which wraps beneath the ventral surface of the tongue. This results in sublingual/lingual swelling and often vomiting if the piece of string is long enough to cause irritation of the stomach or plication of the intestinal tract.
I recall thinking, "This has got to be a rare occurrence. I doubt I will see many cases of this throughout my veterinary career.”
Figure 1B: Thorough inspection shows a sublingual linear foreign body (string from the inside of a golf ball).
Stranger than Fiction
Just like "hardware disease” in cattle, truth is sometimes stranger than fiction. These things happen all the time.
Due to its frequency of occurrence, a sublingual linear foreign body in a young cat is not considered a zebra diagnosis. However, a sublingual linear foreign body in an elderly dog is certainly a zebra diagnosis.
Neoplasia is much higher on the list of differentials in an old dog with sublingual pathology. What is considered a zebra diagnosis in a patient of a certain signalment may be considered common in a patient of a different signalment.
Figure 2A: Ulcerative lesion of the gingival and palatal mucosa over the incisive bone in a 7-year-old Pembroke Corgi.
Figure 1A shows a diffusely thickened tongue with pitting edema and a triangular pattern of ulceration in the frenulum area in a 10-year-old dog. Initially, a biopsy was done due to concern for a neoplastic process, but close inspection at the time of biopsy revealed, in the deepest area of ulceration, a linear foreign body embedded in the sublingual tissues (Figure 1B). This dog enjoyed chewing on golf balls, and he was able to remove the cover and ingested some twine from the inside of a golf ball.
An exploratory laparotomy showed the twine extended into the stomach and intestines, and multiple enterotomies were performed to successfully remove the linear foreign body.
Wegener’s granulomatosis is another zebra diagnosis in the dog. Until 2006, this immune mediated disease was never documented in the veterinary literature.1 It manifests as severely ulcerative or proliferative gingivitis and mucositis, and its aggressive appearance can mimic neoplastic processes such as squamous cell carcinoma.
Figure 2B: Same patient four weeks later after oral prednisone administration.
A 7-year-old neutered male corgi presented with a large ulcerative lesion on his rostral maxilla (Figure 2A) of three weeks’ duration. Prior to seeing me, attempts to treat with clindamycin for two weeks and metronidazole for one week resulted in no change. One incisor tooth fell out prior to presentation.
Interestingly, the dog had had a similar lesion near the rostral mandibular canine tooth five months earlier. The mandibular lesion was treated by his previous veterinarian via excisional mandibulectomy due to a high suspicion of squamous cell carcinoma or other aggressive neoplasia. The portion of mandible was submitted for histopathology, which showed no signs of neoplasia. The maxillary mass was biopsied and this also showed no evidence of neoplasia. Histopathological findings were consistent with Wegener’s granulomatosis, or other immune mediated vasculitis.
The patient was placed on prednisone therapy at 1 mg/kg/d for two weeks, then 0.5 mg/kg/d until the one-month re-examination. One month later, the patient presented with significant clinical improvement (Figure 2B). However, severe gingival recession in the area would necessitate future extraction of four maxillary incisors.
This latter case illustrates a few important clinical points:
* Lesions other than neoplasia can have a very aggressive appearance,
* Incisional biopsy is always a good idea when owners can afford this expense as an initial step rather than an immediate curative attempt,
* Zebras are out there. Be on the lookout!
Dr. Lewis, FAVD, Dipl. AVDC, practices veterinary dentistry and oral surgery at NorthStar Veterinary Emergency Trauma & Specialty Center in Robbinsville, N.J.
Krug W, Marretta SM, de Lorimier LP, White DK, Borst L. Diagnosis and management of Wegener’s granulomatosis in a dog. J Vet Dent 2006;23(4):231-236.