In the previous comments about hearing we focused on the ear and how amazing it is. When we find deafness in a dog, it is most commonly a peripheral component in the ear that has malfunctioned. For a central lesion (brain lesion) to cause deafness there must be extensive damage present within the brain. We would expect to see severe neurologic signs if a dog has a central lesion big enough to cause deafness. This is rarely seen.
But what about the rest of the dogs. Deafness is not that uncommon. So, what’s happening with everyone else?
There are two classifications of deafness related to the peripheral components (most commonly affected areas):
Conduction deafness and Sensorineural deafness. Today we’ll briefly touch on conduction deafness.
Conduction deafness results from any obstruction to the passage of sounds waves from the external environment to the last part of the inner ear (spiral canals). The most common causes of this is in dogs are inflammatory lesions and growths. We also occasionally see it in dogs with chronic ear infections where the skin is so thickened they have a tiny ear canal that is full of wax and debri’s. How many times have you treated your dog’s ear infections (when both ears are affected) only to discover your dog can’t hear you! Their ear is full of ointment and this is a form of conduction deafness, albeit temporary as the hearing should return once all the ointment is removed and the ear swelling improves. Old dogs also get conduction deafness but the exact reason is still being proven. Prominent Veterinary Neurologists believe it may be arthrosis (arthritis) of the little bones in the ears preventing normal movement and conduction of the sound wave or a form of sensorineural deafness.