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Vitiligo
Vitiligo is a hereditary skin disease which is not noticeable at birth. Affected dogs develop bleached splotches of skin that occasionally also affect the hair coat and claws. Most splotches are on the face, especially the bridge of the muzzle or around the eyes. Similar patches also appear on both the mucous membranes (tissues that line the inside of the mouth and nose), and perhaps in the retina (inner layer of the eyeball). The hair that grows on areas affected by vitiligo sometimes turns white. Lesions surround the nares, eyes, anus, mouth and genitals with no inflammation or scaling. Affected areas may re-pigment, remain unchanged or wax and wane. Usually the full extent of the depigmentation occurs within 3 to 6 months of the onset of the disease.
Causes
Many possible causes of vitiligo have been proposed, including stress, infections, mutations, neurological factors, defects of skin pigment receptors, and impaired distribution of skin pigment cells (melanocytes). In addition, the accumulation of toxic products of melanin synthesis, the breakdown of free radical defense and the build-up of excessive quantities of hydrogen peroxide have all been suggested to result in the self-destruction of pigment cells. Many studies have also associated vitiligo with autoimmune diseases. In humans, these autoimmune diseases include autoimmune thyroid disease, insulin-dependent diabetes mellitus, rheumatoid arthritis, psoriasis, lupus, alopecia areata, pernicious anemia, Addison's disease and autoimmune polyendocrine syndromes.
Signs
A mottled loss of pigmentation can occur on all four paw pads. When vitiligo affects only the nose, the condition is sometimes referred to by dog breeders as "snow nose." Sometimes depigmentation only affects the bridge of the nose and the adjacent muzzle areas. This condition has also been termed "Dudley nose" by dog breeders.
Breeds at Risk
Vitiligo is relatively uncommon in dogs and cats. The disease generally develops in animals less than 3 years of age. A marked breed predisposition exists for Belgian tervuren. Other breeds at increased risk are the Rottweiler, Doberman Pinscher, German Shepherd Dog, German Shorthaired Pointer, Old English Sheepdog and Dachshund. The disease occurs with varying amount of severity. No treatment is available. However, compounds derived from black pepper extract have shown potential in animal studies to be effective in treating vitiligo. (Oregon Health & Science University (2008, April 15). Pepper Compound Could Aid Millions With Vitiligo. ScienceDaily. Retrieved March 3, 2011)
"Dudley nose" and "snow nose" conditions have been reported in Golden Retriever, yellow Labrador retriever, Siberian Husky, Alaskan Malamute and other northern breeds.
Although loss of pigment cells (melanocytes) from the skin is almost always the primary and initial symptom in vitiligo, other pigment cells in the body can be affected. Melanocytes are located in the inner ear and vitiligo-associated hearing problems have been reported in some patients. Damage can also occur to melanocytes within the eye which is associated with abnormalities of the retinal pigment and uveitis. Vitiligo is a common manifestation of hypoparathyroidism.
A form of vitiligo involving the nose bridge area has been observed in dogs eating from rubber food dishes that contain p-benzyl hydroquinone. Apparently this chemical is absorbed through and inhibits melanin synthesis. The condition is reversible.4
References
- E. Helen Kemp, Elizabeth A. Waterman and Anthony P. Weetman (2001) Immunological pathomechanisms in vitiligo. Exp. Rev. Mol. Med. 23 July, http://www.expertreviews.org/01003362h.htm
- Scientists Implicate Gene In Vitiligo And Other Autoimmune Diseases
ScienceDaily (Apr. 11, 2007)
- Peter J. Ihrke, Emily J. Walder, Verena K. Affolter, Thelma Lee. Skin Diseases of the Dog and Cat
- Michael D. Lorenz, T. Mark Neer, Paul L. Demars. Small Animal Medical Diagnosis
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