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 inflammtion or scaling. Affected areas may repigment, 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.

A mottled loss of pigmentation can occur on all four pawpads. 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 adjucent muzzle areas. This condition has been termed "Dudley nose" by dog breeders.

"Dudley nose" and "snow nose" conditions have been reported in Golden Retriever, yellow Labrador retriever, Siberian Husky, Alaskan Malamute and other northern breeds.

Causes of Vitiligo

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 defence 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 disease. 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.

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pigment

Dudley nose

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.

Recently, researchers discovered a gene, NALP1, that was key to predisposing people to vitiligo and other autoimmune diseases, particularly autoimmune thyroid disease. About 20 percent of people with vitiligo also get autoimmune thyroid disease. NALP1 is probably a receptor for bacterial or viral signals. There is one medication available (approved for treating rheumatoid arthritis) that blocks an inflammatory pathway thought to be controlled by NALP1. By combining a drug with UV light to improve vitiligo treatment scientist hope to improve treatment vitiligo in people.

Treatment of Vitiligo

The disease occurs with varying amount of severity. No treatment is available.

Adapted from
1. 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
2. Scientists Implicate Gene In Vitiligo And Other Autoimmune Diseases ScienceDaily (Apr. 11, 2007)
3. Peter J. Ihrke, Emily J. Walder, Verena K. Affolter, Thelma Lee. Skin Diseases of the Dog and Cat