Presbycusis – or age-related hearing loss – can have a devastating impact on the quality of life of older people, being strongly linked to social isolation, cognitive decline and dementia. But while dogs will often experience a similar deterioration in their ability to detect and process sound in their later years, little is known about the psychological and social impacts of those changes.
A recent study by the UK-trained veterinary neurologist Natasha Olby and her colleagues at North Carolina State University, published in the Journal of Veterinary Internal Medicine, is one of the first attempts to measure the degree of hearing loss that occurs in aged dogs and the impact it has on their own lives and the relationship with their owner (Fefer et al., 2022).
An overview of past research
Studies in human patients have shown hearing loss is one of the most common signs of ageing, found in one-third of people over 65 years old. Those experiencing presbycusis show a rate of cognitive decline that is 30 to 40 percent faster than those with normal hearing (Fefer et al., 2022). The condition is also more strongly linked to the onset of dementia than other risk factors, such as smoking or hypertension (Fefer et al., 2022).
Earlier veterinary research confirmed that similar changes in hearing do occur in dogs, usually starting between 8 and 10 years of age (ter Haar et al., 2010). Presbycusis affects dogs’ perception of the middle to high frequencies of their auditory range, which extends much higher than that of humans (from 20Hz up to 60kHz).
One leading authority on hearing loss in companion animals, Gert ter Haar, lecturer in small animal surgery at the Royal Veterinary College, London, has suggested that “hearing loss contributes to the lethargy and lack of interest in interaction with the environment that is commonly observed in old dogs” (ter Haar et al., 2010).
Gert ter Haar […] has suggested that ‘hearing loss contributes to the lethargy and lack of interest in interaction with the environment that is commonly observed in old dogs’
He also noted that dogs with presbycusis may be a danger to themselves and their owners: “Dogs with hearing loss are unable to anticipate dangers such as motor vehicles, are easily startled, have an increased tendency to bite and sometimes demonstrate exaggerated barking.”
What’s new in presbycusis?
For their study, Professor Natasha Olby’s team dug deep into the impact of hearing loss on canine behaviour and the relationship with their owners. They recruited 39 elderly dogs whose hearing was examined through brainstem auditory evoked response (BAER) tests. These showed that 19 dogs responded to sounds at 50dB, while 12 were able to detect sounds at 70dB and eight could only hear noises when transmitted at 90dB.
The authors then looked at the relationship between the dog’s hearing loss and the owner’s opinion of their pet’s mental and physical function. They used two validated questionnaire-based methods: the canine dementia scale (CADES) and the canine owner-reported quality of life (CORQ) scales.
The CADES test was created to assess the degree of canine cognitive dysfunction syndrome (CCDS) demonstrated by the dogs based on the owner’s observations of its behaviour at home. The test consists of 17 items relating to factors such as spatial orientation, social interactions, sleep–wake cycles and house soiling. It classifies the dog’s function as “normal” or with “mild”, “moderate” or “severe” deterioration.
In those dogs able to hear sound at 50dB, 60 percent were considered to have normal behaviour, while 50 percent in the 70dB group were reckoned to have moderate dysfunction
This test confirmed the association between the extent of hearing loss and the degree of cognitive dysfunction. In those dogs able to hear sound at 50dB, 60 percent were considered to have normal behaviour, while 50 percent in the 70dB group were reckoned to have moderate dysfunction. Half the dogs that could only hear sounds at 90dB were considered to have experienced severe changes.
The CORQ test was originally designed to assess the owner’s view of the effects of cancer on a dog’s quality of life. With minor changes, it has been shown to be a useful metric for the effects of other conditions by measuring the impact of disease on the animal’s vitality, the quality of companionship provided, whether it appears to be in pain and the effects on its mobility.
The results showed that hearing loss did have a significant detrimental effect on the owner’s relationship with the pet, with major reductions in the vitality and companionship scores in dogs with more severe hearing loss.
What did they conclude?
The authors concluded that “much like people who experience social isolation and depression with presbycusis, dog owners perceive a difference in particular aspects of their dog’s quality of life”.
‘Much like people who experience social isolation and depression with presbycusis, dog owners perceive a difference in particular aspects of their dog’s quality of life’
However, they do suggest that this deterioration in the dog’s physical and mental function does not have to be inevitable. They continued: “Hearing loss may be a field in which intervention could slow the progress of CCDS and therefore the relationships among presbycusis, ageing and dementia deserve further investigation in dogs.”
So, what are the management options for dogs with presbycusis?
One obvious strategy for maintaining a good relationship between a dog with hearing loss and its owners would be the use of the sort of hearing aids used successfully to treat deafness in humans.
External aids, like those used in human medicine, are poorly tolerated by dogs. But in his PhD studies at the University of Utrecht, Professor Gert ter Haar surgically implanted devices into the middle ears of laboratory dogs and was able to show that they did produce some improvement in sound perception (ter Haar et al., 2010). However, that study was published over 12 years ago, and since then, there have been ongoing improvements in the quality of the devices used in human patients. So, Professor Natasha Olby is optimistic that “well-tolerated, affordable hearing aids” will eventually become available for use in dogs.
Currently, there is only one veterinary centre in the world where dogs may be fitted with a custom-made hearing aid. Professor Peter Scheifele’s laboratory at the University of Cincinnati carries out auditory testing of dogs from across the United States, but it will only attempt to insert devices in a minority of cases. “Given the many obstacles to success in this arena, hearing aid use is generally not recommended (for dogs),” he says (Scheifele et al., 2012).
Owners keen to go ahead with the procedure should be warned that the process is costly and time-consuming, and there is no guarantee of success
Owners keen to go ahead with the procedure should be warned that the process is costly and time-consuming, and there is no guarantee of success. Owners must realise that hearing aids will not restore the dog’s hearing to the same level and quality enjoyed before the onset of presbycusis. The dog will need lengthy and intensive training to adapt to the technology. As they do not understand the purpose of this training, they are not motivated to cooperate with the process as a deaf human would. Until more suitable technology for use in a hearing-impaired canine patient becomes available, there is advice available for first opinion practitioners on how to manage the patient and its owner (Scheifele et al., 2012).
Conclusion
If a dog with suspected presbycusis is presented at a veterinary practice, the first step would be to carry out a thorough investigation to eliminate other potential causes of hearing problems, such as foreign objects in the ear canal or an infection. Once confirmed, the veterinarian can offer the owner(s) advice on how to manage the condition.
Clients need to appreciate that hearing is less important for a dog than its other senses, particularly smell, and that dogs can maintain a good quality of life with presbycusis. They should be reassured that training to respond to visual signals and commands helps maintain the bond with the owners, and contrary to the popular idiom, an old dog can learn new tricks. However, vast reserves of patience and the help of an experienced dog trainer will likely be necessary.
The client should also be taught about keeping the dog and their family members safe. They can be shown how to avoid startling the dog if it is sleeping and has to be woken up. Extra vigilance will also be needed to avoid injuries when, for example, the dog is no longer able to hear a car approaching.
