By John R. Lewis, VMD, DAVDC, Founding Fellow, AVDC OMFS

One of my favorite parts of writing the monthly column for Veterinary Practice News is presenting cases to you that are rarely seen, so when you come across them in practice, you will have the answers. These dental "zebras" are rare findings or conditions that you will not see every day, but you will likely see during your career.

According to Wikipedia, the medical term, "zebra," was first used in the late 1940s by Dr. Theodore Woodward, professor at the University of Maryland School of Medicine, who instructed his medical interns: "When you hear hoofbeats behind you, don't expect to see a zebra." This is certainly good advice in Maryland.

Sometimes zebras can be seen in unexpected places. Approximately a decade ago, I was preparing my upcoming Veterinary Dental Forum lecture on the topic of "Dental Zebras," when I saw on the news that two zebras were found roaming the streets of West Philadelphia! The point is this: never say "never," and never say "always" when talking about medical diagnoses and treatments.

Shih zebra?

This column will discuss what is perhaps not a true zebra, since it is not a rare manifestation of a common presentation, but this is a rare finding seen on dental radiographs, nonetheless. Have you ever seen this on a dental radiograph and wondered what it was? This radiograph is from a 15-year-old Shih Tzu that I recently saw.

On intraoral radiographs performed to evaluate periodontal health status of the teeth, we saw multiple cylindrical mineralized structures bilaterally of both the upper and lower lips, with more structures seen on the upper lips (Figure 1). The patient had received prednisone chronically to help combat hypercalcemia associated with primary hyperparathyroidism. The patient also had mild elevations of blood urea nitrogen (BUN) and creatinine levels.

Though this patient had multiple possible reasons for abnormal mineralization of soft tissues, I see these mineralized structures in many of my patients known to have Cushing's disease, patients that are receiving chronic prednisone administration, and in some patients that have not yet been diagnosed with Cushing's disease, but their clinical signs and elevated alkaline phosphatase seen on bloodwork may be supportive of the diagnosis.

The mineralized structures are hair follicles, which appear to be associated with whiskers of the lips. This is likely an early manifestation of calcinosis cutis, where dermal soft tissue structures become abnormally mineralized.

The phenomenon of perifollicular mineralization of the skin has been described in the literature, though I could not find any specific mention of it involving whisker follicles.

Previous studies

Findings in a 1984 experimental study of toy poodle dogs receiving mibolerone as part of a chronic dosing study found that poodles in both the mibolerone-treated group and the propylene glycol-treated control group showed perifollicular mineralization. As both the control group and treated groups showed high prevalence of perifollicular mineralization, the authors concluded the lesion was related to prolonged treatment with mibolerone.

Histological findings included deeply basophilic deposits of mineral in dermal collagen immediately surrounding hair follicles in the glassy membrane that surrounded the external root sheath. The perifollicular mineralization was noted in skin taken from various locations, including skin over the mammary gland, adjacent to the vulva, and over the back all contained the lesion. Of the 22 toy poodles with histologically observed perifollicular mineralization, only three dogs had gross evidence of skin disease.¹

An article from 2019 in Veterinary Dermatology evaluated 147 dogs divided into three groups: 91 clinically normal poodles, 40 clinically normal dogs of other breeds, and 16 dogs with a clinical/histopathological diagnosis of hyperadrenocorticism with the aim of determining if perifollicular mineralization is specific to poodles and if it is always associated with mineralization.

The article's abstract did not specify if the lesion was specific to poodles or whether it was seen in the hyperadrenocorticism group. It was determined perifollicular changes were not always associated with calcium deposition.²

Calcinosis cutis can occur due to multiple reasons, including hyperadrenocorticism, primary hyperparathyroidism, secondary (nutritional, renal) hyperparathyroidism, chronic inflammation, neoplasia, and certain fungal infections. Calcinosis cutis is well recognized in dogs with endogenous and iatrogenic hyperadenocorticism.

In a retrospective study of 46 cases of calcinosis cutis in dogs, Labrador retrievers, Rottweilers, boxers, and Staffordshire terriers were the breeds most commonly affected. Most dogs had either an exogenous or an endogenous source of corticosteroids, with the exception of five dogs with renal insufficiency.³

It may be that mineralization of whisker follicles is an early manifestation of calcinosis cutis. Studies may be warranted to determine if intraoral radiographs provide diagnostic support in screening patients with suspected Cushing's diagnosis.

John Lewis, VMD, DAVDC, FF-OMFS practices and teaches at Veterinary Dentistry Specialists and Silo Academy Education Center, both located in Chadds Ford, Pa.

References

1. Seaman WJ, Chang SH. Dermal perifollicular mineralization of toy poodle bitches. Vet Pathol. 1984;21(1):122-123. https://journals.sagepub.com/doi/pdf/10.1177/030098588402100122
2. Miragliotta V, Buonamici S, Coli A, Abramo F. Aging-associated perifollicular changes and calcium deposition in poodles. Vet Dermatol. 2019;30(1):56-e15. https://pubmed.ncbi.nlm.nih.gov/30461084/
3. Doerr KA, Outerbridge CA, White SD, Kass PH, Shiraki R, Lam AT, Affolter VK. Calcinosis cutis in dogs: histopathological and clinical analysis of 46 cases. Vet Dermatol. 2013;24(3):355-61, e78-9. https://pubmed.ncbi.nlm.nih.gov/23565978