Other causes of deafness in adult dogs include:
- drug toxicity associated with aminoglycosides
- chronic otitis externa
- presbycusis - degenerative age-related deafness
- Waardenburg syndrome
In some breeds, CHSD is associated with a lack of cochlear melanocytes in the stria vascularis, certain coat characteristics, and potentially, abnormalities in neuroepithelial pigment production, such as heterochromia.
In Dalmatians with heterochromia, approximately 20% have congenital deafness or reduced auditory responses as determined by brainstem auditory-evoked responses. In this breed, deaf puppies possess some cochlear hair cells, however during maturity lose all hair cells and are replaced by supporting cells.
Deafness is usually observed clinically form 6 weeks of age and can be confirmed with testing by auditory stimuli, evoked otoacoustic emissions or using brainstem-evoked testing.
Deafness can affect one or both ears, and is an all or nothing phenotype in the affected ear. Bilaterally deaf pups are often identified by breeders without clinical testing, but unilateral deafness is difficult to detect without brainstem auditory evoked response testing.
In solid-colored coat breeds, such as the Doberman, deafness is usually associated with cochlear neuroepithelial degeneration. In other breeds, it is associated with a lack of coat and iris melanocyte pigmentation as well as degeneration of the stria vascularis of the cochlea during the first four weeks of life.
Although deafness in dogs has a limitation for functionality as both work animals and pets, there is no justification for euthanasia of these dogs when diagnosed providing other quality of life parameters are fulfilled.
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