Nail-like Growth on Dogs

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If you're petting your dog and you feel a small, hard growth on the skin that looks like a nail or horn, don't panic. These benign tumors are known as cornifying epitheliomas, or cutaneous horns. They might look unsightly but usually don't cause problems in the dogs who develop them. Take your dog to the veterinarian for a definitive diagnosis and treatment options.

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What are cutaneous horns on dogs?

A cutaneous horn is a hornlike or nail-like growth on a dog's skin that arises through a dog's hair follicle. "Cutaneous" means skin. "Cornifying" means looking like a horny substance. "Epitheliomas" is a medical term for a skin tumor that can be either benign or cancerous, but cornifying epitheliomas in dogs are benign. Cornifying epitheliomas are also known as keratoacanthoma. These epidermal growths contain keratin, which is the protein found in a dog's toenails and fur that is produced by cells called keratinocytes.

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Identifying a cutaneous horn on a dog

A cutaneous horn on a dog will be a growth that sticks up from the skin surface like an animal's horn.‌ While they can develop anywhere, they often appear on the neck, shoulders, back, tail, and legs (including on the footpads.) It can feel like a sticklike growth. They can vary in color, but some are black, gray, tan, or flesh colored.

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While cornifying epitheliomas can look a little like an animal horn, they can also look or feel like hardened spots or hardened cysts. Sometimes, dogs will bite or scratch at these growths, which can cause ulceration, bleeding, or infection.

Since there are other skin diseases and skin cancers, like invasive squamous cell carcinoma and mast cell tumors, that can also cause bleeding or ulceration, your veterinarian may do a fine needle aspirate and/or biopsy with histopathology.

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It is important to get suspected cutaneous horns checked out because they can become more widespread across the body. Also, the appearance of any new growth on a dog, even if it just looks like a wart, should be checked by your veterinarian to determine if it is potentially malignant.

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Why do cutaneous horns grow on a dog?

A cause for why these growths develop is not known for sure.‌ The incidence of cutaneous horns is higher in middle-age dogs. Breeds most affected by cornifying epitheliomas are Norwegian elkhounds, Belgian sheepdogs, Lhasa apsos, and bearded collies. Norwegian elkhounds and Lhasa apsos are also at risk for having these tumors become more widespread, which is referred to as the generalized or multicentric form.

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A chemical called B-catenin can turn skin cells into hair follicles as a dog develops, and overproduction of B-catenin can cause hair follicle tumors to develop. There is a genetic predisposition that makes these tumors more common in certain breeds of dogs. Male dogs are more likely to develop these. Humans can also develop similar hornlike masses (sometimes secondary to human papillomavirus), but cutaneous horns are not spread between dogs and humans.

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Treatment of cornifying epitheliomas on dogs

Sometimes, dogs are annoyed by these growths and will attempt to bite, rub, or scratch them off their skin. If they do this, they can cause an infection or trauma to the area. In this case, your veterinarian might suggest cryosurgery or surgically removing them. In cases where the growths are widespread, oral medications called retinoids can also help.

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Prognosis after treatment with surgical excision is good, as 71 percent of dogs have a complete improvement when treated with surgery, and 29 percent improve with treatment by retinoids, but the tumors commonly return after treatment is ceased.

Monitor the size, shape, texture, and appearance of any cutaneous horn. If it's causing your dog a problem, get it checked out to discuss options for removal. Most cornifying epitheliomas are easily diagnosed and treated by your family veterinarian without the need for a veterinary dermatology specialist.

The bottom line

Cutaneous horns, or cornifying epitheliomas, are benign, hornlike or nail-like growths that arise from a dog's hair follicles. Middle-age dogs are more prone to developing them, as are Norwegian elkhounds, Belgian sheepdogs, Lhasa apsos, and bearded collies. These skin tumors most often develop on a dog's tail, back, legs, neck, or shoulders. Surgical excision is often curative. Even though this growth is benign, any new growth or skin lesion that develops on your dog should be examined by your veterinarian to rule out malignancy.

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