Identifying and managing behavioral changes in older dogs and cats
Sep 01, 2002
Older dogs and cats are the most rapidly growing segment in many veterinary clinic populations. In part, this is because better and more sophisticated treatment for primary medical conditions has lead to longer-living pets. Many of these older animals will be affected by non-specific signs associated with cognitive aging. The proportion of dogs and cats with cognitive decline will increase as they age (e.g., clients will note behavioral changes for more 16-year-old dogs than for those 10 years old). Changes in non-specific behavioral signs associated with aging may not accurately reflect the degree of true cognitive change or "dementia" that the pet is experiencing, but these signs are excellent indicators of client distress. Client distress potentially leads to euthanasia of the pet. We can now do better.
Common client complaints and signs of cognitive decline: The most common changes noted by clients are:
1. Disorientation. The dog or cat seems to get lost in the house, in his or her room, or confused when outside. The pet may become increasingly distressed within each episode of disorientation early on in the progression of the cognitive changes, and less so as the changes become more pronounced.2. Alterations in social and environmental interactions. As cognitive decline progresses affected dogs and cats interact less with their canine and feline housemates, play less, overall, ignored favored toys, and withdraw from clients, often refusing interaction with them. If forced to interact, dogs and cats can become completely withdrawn, or agitated and more distressed, possibly to the extent of becoming aggressive as a means to decrease interaction. When greeted, affected pets appear not to recognize clients. This profound alteration in client interaction and affect is the change that most distresses clients.
3. Changes in diel/sleep-wake cycle. Affected dogs and cats may no longer exhibit standard sleep-wake cycles, instead, pacing +/- vocalization during the night. Cats sleep often during the day as a normal behavior, so these changes may be most noticeable for dogs. Increased vocalization that is repetitive and monotonic is the most common complaint of clients with aging cats. The most distressing aspect of changes in diel for the clients is that they cannot comfort their pets when they pace and vocalize. Early in the progression of the condition diel changes may only be manifest as increases in time spent sleeping, which, unfortunately, may be considered a "normal" aging change.
4. Changes in elimination behaviors. Clients often described cognitive changes associated with eliminative behaviors as "a loss of housetraining." It is likely that changes in memory and learning associated with true housetraining (e.g., the ability to inhibit elimination unless provided with an appropriate substrate) are affected as a result of cognitive changes, but it is important to note that these dogs are not incontinent. The pets either appear to "forget" to eliminate when taken to their normal locations and substrates, and then eliminate anywhere they are when the need is urgent, or they have reduced inhibition and will eliminate wherever they are once they reach a certain threshold stimulus. The extent to which cognition is involved in inhibition of volitional behaviors is largely unexplored in dogs and cats but appears to be important in humans.
Accordingly, cognitive dysfunction is best defined by the following conditions: a change in interactive, elimination, or navigational behaviors, attendant with aging, that are explicitly not due to primary failure of any organ system, and that are not consistent with the definitional criteria for any anxiety disorder. Organ system dysfunction that could contribute to the non-specific signs discussed are found in Table 1. The minimum recommended database required to exclude any of these systemic conditions is found in Table 2.
It should be obvious that physical ability, or lack thereof, could confound how the client perceives the extent to which the complaint is behavioral or physical. A check sheet should be completed by clients at every annual visit. This way, not only will the clients watch for signs that may be early indicators of impending cognitive decline, but the physical contribution to the cognitive changes will be assessed in a routine manner along with the behavioral component. By having the clients complete such check sheets each time the dog or cat is seen, changes will be noted in a more accurate manner than one that depends on the client's memory, alone. This check sheet can also be used to assess whether the animal has improved post-treatment.
Changes in neurochemistry. It should be noted that the diagnosis of cognitive dysfunction or decline is a phenotypic one based on how the behaviors look. This does not imply that any specific underlying neurocellular mechanism is responsible for the changes noted. Recent advances have indicated that afflicted dogs may have variable amounts of cellular and neurochemical changes that are, themselves, rooted in different molecular processes. Age-related declines are generally associated with vulnerability of the cholinergic neurons. Such vulnerability could be the level of the cholinergic neuron, itself, the neurotrophic support system, cytoskeleton alteration, target loss, and vascular dysfunction. We know so much about canine behavioral changes that occur with age because dogs are good neuroanatomical and neurobehavioral models for humans because the non-specific behavioral changes associated with aging are shared by humans and dogs.
Changes in brain pathology that aged dogs share with aged humans with a diagnosis of one form of human dementia (Alzheimer's disease) include (1) thickening of the meninges and dilation of the ventricles, (2) age-related gliosis, (3) vascular changes, (4) diffuse plaques, and (5) amyloid deposition. Dogs do not seem to form the true neurofibrillary tangles that humans form.