Slick is an 11-year-old black Labrador retriever. At least, she used to be black. Perhaps she got tired of the ubiquitous Black Dog of Martha’s Vineyard. Perhaps she has always harbored secret dreams of being a dalmatian. All I know is that when Slick arrived for her annual checkup, where once she had been solid obsidian black, she was now dappled with spots of pure white spots. Not just a few flecks here and there, but sizable splotches all over her face and body. It’s not unusual for senior dogs to go a little gray, but this was different. “So what do you think about this coat?” her owner asked.
A dog’s coat color is determined by several factors. Cells called melanocytes synthesise various types of the pigment melanin. These are transferred to the hairs, creating different coat colors, depending on the exact types and amounts of melanin. This is primarily controlled by Slick’s genes, but other factors such as nutrition, hormones, and drugs can also affect melanin production. With age, the number of melanocytes often declines, causing graying. That’s normal. But Slick’s transformation was dramatic. Was this just an unusually pronounced aging change, or could it indicate serious underlying disease? I ruffled her fur, examining the skin below. It looked completely normal. “Well, dogs do get vitiligo,” I mused.
In humans, vitiligo is a disease that occurs when melanocytes die or stop functioning, resulting in loss of skin color in blotches. It can affect any part of the body, including hair and eyes. Proposed causes include hereditary, immune-mediated disease, and trigger events such as sunburn, stress, or chemical exposure. In dogs, vitiligo is uncommon, but when it does occur, it most commonly presents as loss of skin pigment on the nose, lips, face, and footpads. Belgian Tervurens, German shepherds, Rottweilers, and Doberman pinschers are the most frequently affected breeds. The white patches almost always start on the nose, and have a typical “spotty” distribution. This differentiates it from a far more common condition called “nasal depigmentation.”
Also known as “snow nose,” nasal depigmentation is a quirky condition in which a dog who starts out with a black or dark-brown nose changes to have a light brown or whitish nose. Sometimes the color comes and goes seasonally, hence the name “snow nose.” It is most common in golden retrievers, yellow Labrador retrievers, Siberian huskies, Alaskan malamutes, and some terriers as well. Despite the name “snow nose,” the condition does not seem to be linked directly to cold temperatures, as it does occur even in warmer climates, but many believe it is the shorter daylight hours during winter, combined with a genetic component, that trigger the transient loss of pigment. Although sometimes the color loss is permanent, usually it comes and goes year after year.
The term “Dudley nose” is also occasionally used to refer to a dog with a pink or liver-colored nose. Some people use this term interchangeably with “snow nose,” but dog aficionados generally reserve “Dudley nose” as a pejorative term to describe a dog with a permanent lack of nasal pigment that is considered a fault in certain breeds and disqualifies them from the show ring. I have found several explanations of the origin of this term. There is a town called Dudley in the West Midlands of England where bulldogs with flesh-colored noses were reportedly bred. Other sources suggest the term dates back to 1877 to a bulldog named Lord Dudley, who had liver-colored nose and lips. Whatever you call it, as long as the lack of nasal pigment is not associated with lesions on the nose such as crusts, scales, or oozing sores, it’s usually benign and primarily a cosmetic problem that bothers the owner more than the dog. A little sunblock is good if Dudley is out in the sun, but otherwise, no worries.
There is, however, one rare condition in which nasal depigmentation signals a serious disease: canine uveodermatologic syndrome. Thought to be an inherited autoimmune disease, its highest incidence is in young adult to middle-aged Akitas, but it has also been reported in the Siberian husky, Samoyed, chow chow, Irish setter, dachshund, fox terrier, Shetland sheepdog, Saint Bernard, Old English sheepdog, and Fila Brasileiro. Symptoms include well demarcated, symmetrical depigmentation of the nose, lips, and eyelids. Sometimes other areas, such as footpads or skin around the genitals, also lose pigment, and there may be generalized depigmentation of the hair coat. Dogs with uveodermatologic syndrome develop severe ophthalmic disease at around the same time that they start to lose pigment, and can quickly go blind. Early, aggressive intervention may prevent loss of vision, but lifelong therapy with corticosteroids is generally required, and the prognosis is only guarded to fair.
Slick seemed perfectly healthy. Her nose was still mostly black as coal. Her skin looked fine. She had no clinical symptoms of any kind. Just her big white spots. “Let me read up a little and I’ll get back to you,” I told her mom. “Maybe she’ll be in your next column,” she replied. Uh huh.
My research yielded a vocabulary list. Poliosis: graying or decrease in pigment of the hair. Leukotrichia: lack of pigment in hair, i.e., completely white. Leukoderma: lack of pigment in skin, i.e., completely white or pink. As is often true with dermatology, I could make a fancy- sounding diagnosis which was really just a descriptive name based on the appearance. For anything more definitive, we would have to determine the underlying condition. This might require skin cytology, fungal cultures, skin biopsies, bloodwork, endocrine testing, even genetic testing. Without nasal depigmentation, Slick probably didn’t have vitiligo, which technically is “a specific immune-mediated condition causing leukoderma and/or leukotrichia.” Hard-pressed to advise Slick’s owners to spend hundreds of dollars when she seems perfectly healthy (albeit spotty), I am advising they watch for any signs of illness, but for now, we’re chalking it up to a diagnosis of “multifocal areas of leukotrichia and poliosis.” Sounds good.