Colour Dilution Alopecia
Also known as: Colour mutant alopecia — Blue Doberman syndrome — blue dog disease
Colour dilution alopecia is a form of hair follicle dysplasia. It is relatively common in dogs with a blue or fawn dilute hair colour, mainly Blue Doberman Pinschers but also the Dachshund, Great Dane, Whippet and Poodle amongst others. It has also been seen in blue or cream-coloured cats that express the Maltese dilution gene. In general, the lighter the hair colour, the more severe the disease.
Colour dilution alopecia is associated with a colour dilution gene, probably at the D locus. Under the influence of multiple genes, dliute hairs form with larger, abnormal pigment granules due to abnormalities in melanin transfer and storage. This pigment clumping leads to washed out, or dilute colours. It is not known if the colour dilution gene is directly reponsible for the skin changes or if a linked gene codes for the associated follicular changes. The clumping of pigment leads to distortion of the hair shafts and fracture resulting in alopecia. Also, signals from melanocytes are important in initiating the anagen phase of hair growth and lack of signal might lead to resting, non-cycling follicles.
Onset of the condition can vary from 6 months to 2-3 years of age.
A condition called Black Hair Follicular Dysplasia has also been described, which consists of similar lesions but confined to dark-haired areas of light-coloured dogs with darker spots. It can probably be seen as a localised colour dilution alopecia due to a similar colour-related genetic defect.
There is gradual onset of a dry, dull, brittle and poor quality hair coat.
Hair shafts break and regrowth is poor, resulting in a progressive, partial, patchy alopecia and stubble that precedes a more complete hair loss.
Lesions are usually more severe on the dorsal trunk.
Chronic cases can show hyperpigmentation, and scaling and secondary bacterial infections can occur.
Lesions will be limited to the dilute-coloured parts of the coat in multi-coloured animals.
Clinical signs are suggestive.
Hair should be examined microscopically and might demonstrate uneven distribution and clumping of melanin which distorts the hair shaft.
Skin biopsy and histopathology showing macromelanosomes, melanin clumping and follicular dysplasia, will confirm the diagnosis.
There is no effective treatment for this disorder. The disease is progressive and incurable, but some palliative measures can be taken early on in the course of the disease.
Hair loss due to shaft fracture can be minimised by avoiding excessive brushing and shampooing. Moisturisers may help make the hair less brittle and gentle bathing with antimicrobial and keratinolytic products can be tailored to the needs of the individual case.
Folliculitis should be treated with systemic antimicrobial therapy.
If scaling is severe, oral vitamin A or synthetic retinoids may help.
A high-quality diet and essential fatty acids might also be beneficial.
Patel, A. (2008) Small animal dermatology Elsevier Health Sciences
Gross, T. L. (2005) Skin diseases of the dog and cat: clinical and histopathologic diagnosis Wiley-Blackwell
Harvey, R. (2009) A colour handbook of skin diseases of the dog and cat Manson Publishing
Mecklenburg, L. (2009) Hair loss disorders in domestic animals John Wiley and Sons