Cases reported to practitioners

In a Spanish study of 270 dogs over 7 years of age presented for behavior problems, 74% of the owners detected at least one behavior problem, two problems in 19.8%, three in 4.6%, and four in 1.3%. Thirty-two percent displayed aggression to family members, 16% aggression to family dogs, 9% barking, 8% separation anxiety, 6.4% disorientation, 6% aggression towards unfamiliar people, 5% housesoiling, 4.2% destructive, 4% compulsive disorders and 3% noise fears.³ Sixteen percent of these cases were diagnosed as CDS. In a second study at a behavior referral practice in St. Louis, of 103 senior dogs, 30% displayed separation anxiety, 27% aggression to owners, 17% aggression to other dogs, 8% compulsive disorders, 5% phobias, 4% anxiety, 3% housesoiling and 1% vocalization. Seven percent of these cases were diagnosed as CDS.⁴ When examining the distribution of behavior cases in dogs of all ages, aggression is by far the most common reason for referral with various forms of anxiety (independent of aggression) representing 15% of the cases or less, while in senior pets behavior problems associated with anxiety appear to be the most common reason for referral (Table 13.1).

Table 13.1 Canine senior case distribution compared to case distribution of all ages

¹Horwitz D. Dealing with common behavior problems in senior dogs. Vet Med 2001;96:869–887.

²Bamberger M, Houpt KA. Signalment factors, comorbidity, and trends in behaviour diagnoses in dogs: 1644 cases (1991–2001). J Am Vet Med Assoc 2006;229:1591–1601.

In 83 senior cats referred for behavioral consultations, most cats displayed signs of marking or soiling (73%); however, cases of aggression (16%), vocalization (6%), and restlessness (6%) were also serious enough to require referral.¹ When examining the distribution of behavior cases in cats of all ages, there appears to be a strong similarity in distribution, except for a relative increase in vocalization and restlessness in senior cats (Table 13.2).

Table 13.2 Feline senior case distribution compared to case distribution of all ages

^*Cases recruited from behavior referral practices: Landsberg (n = 25), Horwitz (n = 33), Chapman BL, Voith VL (n = 25).²

¹Bamberger M, Houpt KA. Signalment factors, comorbidity, and trends in behaviour diagnoses in cats: 736 cases (1991–2001) J Am Vet Med Assoc 2006; 229, 1602–1606.

²Chapman BL, Voith VL. Geriatric behavior problems not always related to age. DVM Newsmagazine 1987;18:32.

To examine further the distribution of problems reported by owners in senior dogs and cats, the Veterinary Information Network database (www.vin.com) was searched for the most recently reported behavior problems of 50 senior dogs (aged 9–17) and 100 senior cats (aged 12–22 years). In the dogs, there were 37 cases with signs of anxiety (fear, vocalization, salivation, destructiveness, hypervigilance); 18 with separation anxiety; 13 “wandering”; 11 night anxiety or waking; 9 noise phobias; 7 vocalizing; 2 with stereotypies; and 2 aggressive. Thirty-one dogs had signs consistent with CDS. In the cat cases, 61 were vocalizing excessively (31 at night); 27 had inappropriate elimination; 22 were disoriented; 19 were wandering; 18 were restless; 6 were irritable or aggressive; 4 were fearful or hiding; and 3 were more “clingy” with owners. Since any of these signs can be due to underlying medical problems, this demonstrates the importance of identifying behavioral signs in maintaining the health and welfare of senior pets. While cerebral disease, hypertension, sensory decline, pain, metabolic or endocrine diseases, anemia, neoplasia, drugs or viral agents (e.g., feline immunodeficiency virus) were all considered, in most cases these had been ruled out.¹

Prevalence of behavioral signs in senior pets

When focusing on the problems that are serious enough for pet owners to seek behavioral guidance, it is much more common for senior pets to go unreported unless practitioners take a more proactive approach in educating pet owners about the significance of behavior changes in older pets and actively inquiring about their presence. In 2005, the American Animal Hospital Association (www.aahanet.org) senior care task force published guidelines which included annual wellness examinations and laboratory screening for middle-aged pets and twice-yearly screening for senior pets. In addition, a critical component of the guidelines as well as those of the 2008 American Association of Feline Practitioners (www.catvets.com) senior care guidelines is the questioning of pet owners to determine if any changes have occurred in their pet’s health or behavior. Often the signs are mild or subtle and not necessarily a concern for the owners. In addition, if veterinarians do not educate owners that these signs might be indicative of emerging health and welfare concerns and that many of these problems can be resolved or improved if diagnosed early, the owners will not know the importance of reporting these signs. One practical and efficient way to ensure that signs are identified and recorded is to develop or utilize a questionnaire that the owner can complete at each visit and that is kept in the medical record for future comparison (Form 13.1). A separate and more detailed cognitive questionnaire might also be utilized to record and track behavioral signs for pets in which changes have already been identified (Form 13.2).

It is clear from the publication of numerous prevalence studies that owners do not voluntarily report many of these behavioral changes. In one study owners of dogs aged 11–16 that had no health or behavioral abnormalities noted on their medical records during the annual visit were called to inquire retrospectively if there were any noticeable behavioral changes. Twenty-eight percent of 11–12 year-old dogs and 68% of 15–16-year-old dogs had at least one sign of DISHA.⁵ In another study, CDS was diagnosed in 14 dogs that had visited the veterinarian for a routine annual check-up and reported no behavioral complaints until actively questioned by the veterinarian.⁶ In an Italian study, 124 dogs over 7 years of age were evaluated and, after eliminating 22 with medical causes, 41% had alterations in one category and 32% had signs in two or more categories; therefore at least 73% had signs.⁷ In another study, the prevalence of CDS in 325 dogs over 9 years of age was 22.5%.⁸ Social interactions and housesoiling were the most commonly reported signs. Females and neutered males were significantly more affected than intact males. One previous study also identified a trend toward a higher prevalence in neutered males.⁹ A recent study based on a large internet survey reported a prevalence of 5% in dogs 10–12 to 23.3% in dogs 12–14 and 41% in dogs over 14, with an overall prevalence of 14.2%.² Once clinical signs are identified, the prevalence and severity of signs increase with age.^2,8,10 Studies of behavior signs in aged cats are lacking. However, in one study of 154 owners of cats aged 11 and older, after eliminating 19 cats with medical problems, 35% of the cats were diagnosed with CDS – 28% of 95 cats aged 11–15, and 50% of 46 cats over 15 years.¹¹ In addition, estimates of the prevalence of CDS in dogs and cats are likely greatly underestimated since deficits in learning and memory likely arise several years before the first clinical signs of cognitive decline appear (discussed below).

It is therefore the role of the veterinarian and staff to inform and educate clients of the importance of reporting these signs. Handouts and web links can be used to educate owners further about geriatric care and questionnaires can be used to screen for problems quickly and extensively at each visit (Forms 13.1 and 13.2).

Medical causes

Medical differentials for behavior problems are discussed in detail in Chapter 6 (see Table 6.1). However, the practitioner should focus on disease processes that are most likely to affect senior pets. The aging process is associated with progressive and irreversible changes that can affect behavior. In fact, any disease that affects the central nervous system (CNS: including hepatic encephalopathy, tumors, CDS) or its circulation (e.g., cardiac disease, anemia, hypertension) can affect behavior.

Behavior and memory circuits are mainly located in the forebrain, including the limbic system and hippocampus. Therefore a change in personality or mood, inability to recognize or respond appropriately to stimuli, and loss of previously learned behavior might be indicative of forebrain involvement. In some cases, there may also be other concurrent signs such as cranial nerve involvement, seizures, motor deficits, or emesis. Alterations in awareness and responsiveness to stimuli and consciousness might arise from disease of the brainstem or forebrain, as well as from deficits in the sensory system. Pain (e.g., due to arthritis, dental disease) can lead to irritability and fear of being handled. If mobility is affected, the pet may become increasingly aggressive, or may have more difficulty accessing its elimination area. Organ failure, tumors, degenerative conditions, immune diseases, and endocrinopathies, (e.g., hyperadrenocorticism), are more common in older pets and can all affect behavior. Therefore medical screening (physical examination and laboratory tests) is an essential first step in the workup.

If medical problems are diagnosed, it can be a challenge to determine whether the problem is actually causing the behavioral signs. Response to therapy may therefore be an important step in the workup (see Chapter 6 for details). Unfortunately, with age not all medical problems can be resolved or improved and some may continue to progress. Therefore, the owner should be provided with realistic expectations and modifications may be required to the pet’s environment or schedule to help the family and pet best manage the situation.

Threshold

Even with a comprehensive medical assessment and successful treatment of underlying medical problems, the behavioral signs may persist. One explanation is that it can take multiple stimuli to “push” the pet beyond a threshold to where a behavior problem is exhibited. For example, a pet with painful arthritis that also begins to lose hearing and sight may startle and become more aggressive when handled or approached by people (e.g., strangers or young children) that the pet previously would have avoided. The threshold has been surpassed by combining pre-existing avoidance behaviors with sensory decline and pain. Therefore the same pet may still accept or tolerate the handling and physical contact of its favored family members. Medical conditions (e.g., gastrointestinal disturbances, metabolic disorders) might also lower the threshold (level of tolerance), leading to an increase in frequency or severity of anxious or phobic behaviors.

Primary behavior problems

Changes in the pet’s environment may also contribute to the emergence of behavior problems. Schedule changes, a new member of the household (e.g., baby, spouse), a new pet, and moving can have an impact on a pet’s behavior. This is of particular concern in the older pet which may be more sensitive and less adaptable to change. Another concern is that even if medical problems can be effectively resolved, the behavior problem might persist if the pet has learned that aggression can successfully remove threatening stimuli, or if it has learned that there are new indoor locations and surfaces on which to eliminate. An extensive history is therefore required to determine if there are environmental factors, relationship issues and family responses (consequences), or learned factors that might have played a role in the cause or persistence of a behavioral problem.

The role of stress in health and behavior

As discussed in Chapter 6, stress can contribute to both health (e.g., dermatologic, gastrointestinal, aging) and behavioral problems (e.g., anxiety, compulsive disorders). Stress is an altered state of homeostasis which can be caused by physical or emotional factors. In the aging pet, there is a general deterioration in physical condition, tissue hypoxia, alterations in cell membranes, increased production and decreased clearance of reactive oxygen species, a decline in organ, sensory, and mental function, a gradual deterioration of the immune system, and decreased ability to cope with change. Thus, the senior pet in particular is less able to respond to stress and maintain homeostatic balance. Owners should be encouraged to maintain a stable and predictable environment and schedule; to plan and make any necessary changes gradually; and to monitor pet enrichment programs, especially for cats (see below) to ensure that they have a positive and desired effect.

Cognitive dysfunction syndrome

CDS is a neurodegenerative disorder of senior dogs and cats that is characterized by increasing brain pathology and gradual cognitive decline.^1,12–19 The development and validation of tests for assessing cognitive function in dogs, including discrimination, oddity, reversal, attention, and spatial memory, have been instrumental in documenting tasks on which senior and old dogs cannot succeed as well as adult dogs^{1,17,18,20,21} (Figures 13.1 and 13.2); cats can be tested as well (Figure 13.3). For example, visual discrimination learning (learning which of two objects covers a reward) is not usually affected by age in most animals, including dogs. However, if the task is more difficult, such as in size discrimination (i.e., the dog must learn whether a small or large object covers the food; Figure 13.4), aged animals have more difficulty in learning the task compared with younger animals. Tasks requiring the inhibition of a previously learned behavior, as in reversal learning (the dog must learn that the food is now under the opposite object), are also sensitive to age.¹⁸ This may be due to the fact that reversal learning but not discrimination learning in dogs requires the intact function of the prefrontal cortex. This is a brain region in dogs in which the earliest and most consistent neuropathology tends to arise. Memory decline in dogs is also age-dependent. Using memory tasks, such as where the dog is required to recall which object covered the food after gradually longer delays, some aged dogs are unable to remember the location of an object seen 5–10 seconds previously.²² Memory testing reveals three groups of aged dogs: (1) unimpaired; (2) impaired; and (3) severely impaired (Figure 13.5). This is consistent with the findings in the geriatric human population. Laboratory studies have identified altered sleep–wake cycles, increased stereotypy, decreased social contact with humans, and a decreased interest in exploration and play with toys in dogs with cognitive impairment²³ (Figure 13.6).

Figure 13.1 Toronto General Test Apparatus. In discrimination learning the dog or cat learns to find food under one of the objects (e.g., the large object), the position of which is randomly presented. When discrimination learning reaches criterion (over 70% success), the dog or cat can then be tested on reversal learning where the food is presented under the opposite (small) object, until the pet reaches criterion. This task is significantly more difficult for senior dogs and cats to learn compared to young adults.

(Courtesy of CanCog Technologies.)

Figure 13.2 Object discrimination learning is not sensitive to age in dogs (correlation between age and error scores on object discrimination is r = 0.05). In contrast, size discrimination error scores increase significantly with age (correlation between age and error scores on size discrimination is r = 0.728).

(Reproduced from Head E, Callahan H, Muggenburg BA, et al. Discrimination learning ability and beta amyloid accumulation in the dog. Neurobiol Aging 1998;19:415–425, with permission from Elsevier Science.)

Figure 13.3 Feline testing. Cat being tested on two-choice memory task (delayed nonmatching to position position: DNMP).

(Courtesy of CanCog Technologies.)

Figure 13.4 Four-choice attention task. Neuropsychological testing. In this task the dog must find the food under the correct (different) object when 0, 1, 2, or 3 incorrect objects (distracters) are presented concurrently.

(Courtesy of CanCog Technologies.)

Figure 13.5 Spatial memory is unimpaired, impaired, or severely impaired in three different subsets of aged dogs.

(Reproduced from Head E, Milgram NW, Cotman CW. Neurobiological models of aging in the dog and other vertebrate species. In: Hof AP, Mobbs C (eds) Functional neurobiology of aging. Academic Press, San Diego, CA, 2001, pp. 457–468, with permission from Academic Press.)

Figure 13.6 The amount of time spent playing or contacting the various toys in the room is plotted against cognitive group. Young dogs play with the toys more than age-impaired (P < 0.027) dogs, who rarely touched the toys. Aged, unimpaired dogs explored the toys a little.

(Courtesy of Christina T Siwak.)

To date, similar laboratory models in cats have been inconsistent. In one study, deficits in eye blink conditioning, found in Alzheimer’s patients, were also demonstrated in a subset of aged cats.²⁴ In a second study, evaluating performance on a hole board task, aging did not appear to affect spatial learning but working memory errors were identified.²⁵ Recently CanCog Technologies (www.cancog.com) has modified the canine test apparatus and protocols for use in cats. Preliminary data demonstrated age differences, with senior cats being impaired relative to normal adults.²⁶ This feline battery should be instrumental in determining the relationship between brain pathology and CDS in cats as well as in the development of therapeutic interventions.

Based on clinical signs alone, CDS has been traditionally diagnosed in dogs at 11 years and older. However, dogs show impairment in the spatial memory task as early as 6–8 years of age.¹⁹ These functions are highly dependent on the frontal lobe, which shows atrophy and beta-amyloid accumulation prior to other brain areas.¹⁴ In cats, cognitive and motor performance appears to decline starting at approximately 10–11 years of age, but functional change in the neurons of the caudate nucleus has been seen as early as 6–7 years.^25,27,28