What Causes Deafness in Dogs?

 Basically the problem is in the ear or in the brain.  In some types sound waves do not reach the nerves of the ear.  Inflammation of the outer ear and and ear canal diseases can cause deafness by way of narrowing the ear canal, tumors, or a ruptured ear drum.  Nerve and degenerative changes in elderly dogs can cause deafness. 
Anatomic disorders — poor development (or lack of development) in the part of the ear that contains the nerve receptors used for hearing.  This condition leads to fluid build-up in specific areas of the brain and damages the part of the brain involved with hearing.  Tumors or cancer involving the nerves used for hearing.  And of course infectious disease, inflammation and trauma such as caused by distemper. In addition to all that, there is idiopathic deafness caused by:

• Toxins and Drugs
• Antibiotics
• Antiseptics
• Chemotherapy drugs
• Medications to remove excess fluid from the body
• Heavy metals such as arsenic, lead, or mercury
• Products used to break down waxy material in the ear canal

Then there are the slow processes that cause deafness over time, such as inflammation of the outer, middle, or inner ear.  And genetic causes which are part and parcel to certain breeds having a white coat color.  Dalmatians are probably the most well known deaf prone dogs. 

 Blocked ear canals can result in deafness from the blockage itself or from a secondary infection. This condition is most common in breeds with narrow ear canals and coarse, wiry hair (poodles and some spaniels). When wax, debris, hair or a foreign object become lodged in the ear canal it  the pup's ability to hear.  Fortunately, this kind of deafness will be cured upon removal of the object.  Unfortunately, foreign objects can wound the ear and debris can allow microbes to grow resulting in infection that can destroy nerves and other tissues, leading to permanent hearing loss. A veterinarian can remove ear debris and prescribe antibiotics or antifungals to treat ear infections.

Hunting dogs are prone to deafness from noise trauma, the result of shotgun blasts close to sensitive ears. Police and rescue dogs regularly exposed to sirens and other loud noises can also suffer this kind of noise-related damage. Age-related hearing loss can be related to overt noise trauma over time, or the result of many small assaults to the inner ear sustained over a lifetime. It can also result from circulatory problems—sensory nerve cells in the ear die off when the blood supply is shunted away from them.

Some breeds and color patterns are known for having a high probability of deafness. The dalmatian is the most well-known breed, but beagles, bull terriers, collies, sheepdogs and any breed with a piebald coat (black or brown and white) or a merle coat (one with light and dark shades of a single color) are susceptible to hereditary deafness. White individuals from breeds that usually have dark coats are also prone to deafness. There is not a "deafness gene" per se; rather, deafness is a side effect of several genotypes that control pigment. The ultimate cause of pigment-related deafness is not fully understood, but the Deaf Dog Education Action Fund says, "If there is unpigmented skin in the inner ear.  The nerve endings atrophy and die off in the first few weeks of the puppy's life, resulting in deafness. Puppies may also be born deaf, which is most common in white or merle-patterned individuals.

Sudden deafness is a fairly rare side effect of several drugs. Aminoglycoside antibiotics (many of the "mycins") can kill off the cochlear hairs, the tissues that allow the ear to sense air vibrations as sound. General anesthesia can also cause deafness. The reason why is not fully understood, but it's speculated that this is the result of a sudden drop in blood pressure that deprives inner ear nerves of oxygen. And finally, some hearing loss in dogs is related to consumption of aspirin (one of the few human painkillers considered safe for dogs). As yet we don't know why, but it may be related to circulation.  All drug-related deafness is considered permanent.

Dog breeds susceptible to congenital deafness:

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