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    Color Dilution Alopecia

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    Overview

    Color dilution alopecia is a relatively uncommon hereditary skin disease seen in dogs with blue or fawn coats, which are dilutions of black and brown, respectively. Irregularities in melanin transfer and storage cause dilution. This syndrome is associated with a color-dilution gene. The initial clinical signs are the gradual onset of a dry, dull, and low hair coat quality.

    Hair shafts and hair regrowth are poor, and follicular papules may develop and progress to frank comedones. Hair loss and comedo formation are usually most severe on the trunk, especially color-diluted areas on the skin. The alopecia is irreversible. Affected dogs should not be used for breeding. Color-dilution alopecia is chronic and poorly responsive to treatment.

    Susceptible Dog Breeds

    The highest incidence is in the blue Doberman Pinscher (93%) and fawn Irish Setter (73%). Other breeds in which color dilution alopecia has been observed include:

    Signs & Symptoms

    The first signs are notable between 6 months and 3 years of age. Patchy hair loss on the ears, head, and along the spinal column seems to be the most common symptom. Dermatitis, wrinkled skin, allergic skin reactions also occur. Some dogs are free of symptoms early in life and then develop them later. Recurrent pyoderma is common. Pruritus (intense itch) occurs if secondary pyoderma is present. Dry scaling is common and usually severe. Papules and pustules (cystic hair follicles with secondary bacterial infection) are also commonly seen. The trunk is most severely affected, while the head and extremities are least affected. Tan points remain normal.

    Appearance

    Coat color dilution leads to the so-called blue pigmentation type in black-and-tan Pinschers (Doberman Pinschers, German Pinschers, Miniature Pinschers), characterized by a silver-blue shade of the black fur areas.

    Note the coat color differences between the two animals. The black and reddish fur parts of the black-and-tan Doberman Pinscher are changed to paler coloring in the blue dog. Classical genetics states that the blue dog is homozygous for the recessive dilute allele.

    Similarly, coat color dilution is responsible for the Isabella fawn phenotype in brown-and-tan or tan Pinschers. Color dilution in Pinschers is inherited as a Mendelian autosomal recessive trait. Although there are no severe impairments known, this pigmentation variation is of clinical relevance as Pinschers with coat color dilution show an increased prevalence of color dilution alopecia (CDA), also called Blue Doberman syndrome.

    Diagnosis

    A preliminary diagnosis is made from a direct examination of the hair shafts. Biopsies show characteristic epidermal, follicular, and pigmentary changes.

    Management

    The treatment goal is to keep the follicles open and free of keratinous debris to prevent secondary infections. Benzoyl peroxide shampoo (oxyDex, SulfOxyDex, Pyoben) is especially effective because of its follicular flushing and antibacterial activity. Prevent dry scales from worsening, with baths of benzoyl peroxide followed by a moisturizing rinse. For dogs with extremely dry skin, the rinses can be diluted and sprayed on daily.

    Antibiotic Use

    Systemic antibiotics are indicated when secondary pyoderma develops. Coexisting diseases, such as hypothyroidism should also be treated since this may improve the dry skin and decrease the incidence of recurrent pyoderma.

    Cephalosporins are often used to treat canine skin infections because of their broad antimicrobial spectrum, established safety profile, and reasonable cost. Cephalexin, cefadroxil, and cephalothin have all been recommended for use in treating canine pyoderma. Recently, cefpodoxime proxetil was approved for treating skin infections in dogs. Once-daily administration sets it apart from other oral cephalosporins used in veterinary medicine.4

    References

    1. Kim et al. – Color-dilution Alopecia In Dogs
    2. Campbell, Miller, Griffin – Muller and Kirk’s Small Animal Dermatology
    3. Nesbitt & Ackerman – Canine & Feline Dermatology
    4. Reddy et al. – Efficacy Of Cefpodoxime With Clavulanic Acid In The Treatment Of Recurrent Pyoderma In Dogs
    5. Philipp et al. – Polymorphisms Within The Canine MLPH Gene Are Associated With Dilute Coat Color In Dogs
    6. Image Credits: Caroldermoid, WikiMedia

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