Canine cognitive dysfunction

Introduction to CCD

Canine cognitive dysfunction (CCD) is a form of dementia affecting geriatric dogs 1 and although it cannot be cured, the clinical signs can be managed and the prognosis improved with early detection and intervention 2,3. The condition is probably more common than is generally recognized 4 as dog owners often attribute the signs to part of the normal aging process and/or believe they are untreatable 5, and so do not discuss their concerns with their veterinarian 1. Indeed, it has been estimated that somewhere between 22.5-68% of elderly dogs express at least one sign of cognitive dysfunction 1,3,6, although this does not mean they necessarily have CCD, as the signs may be associated with other issues such as chronic pain. Accordingly, CCD is an important disease for veterinary professionals to be aware of, and it should be proactively discussed with owners in order to improve the health and welfare of elderly pet dogs (Figure 1). This article will consider the key signs, diagnosis and differentials of CCD, and discuss treatment options and the outlook for the condition.

Presentation and etiology

CCD is a condition of older age, and therefore occurs in geriatric patients; it is commonly reported from 11 years of age, although this varies with the size of the dog and the typical life expectancy of the breed. In some studies females are reported to be more likely to be diagnosed with CCD 1. However, castrated male dogs and smaller dogs are believed to be more prone to demonstrating signs of CCD, and castrated dogs may deteriorate more rapidly 6.

The behavioral signs of CCD are frequently described using the acronym DISHA 7 (Table 1), but the acronyms DISHAA and DISHAAL may also be used, with the additional A standing for anxiety or apathy, and the L for learning 7,8. Regardless of the preferred acronym, it is important to appreciate that there are wider emotional issues in many cases relating to temperament, mood and immediate emotional responses, such as depressive states, poor frustration tolerance or increased attention seeking, in addition to the more classic avoidance responses associated with anxiety. Table 1 reviews the classic signs relating to DISHA and important differentials to consider. Dogs vary enormously in the reported signs in the initial stages, with no consistent pattern evident 9, so early detection can be challenging. However, CCD is a progressive disease and so further signs are commonly reported over time, which means it is important to monitor these cases from the first time a sign is noticed, even if a diagnosis is not made at that time. Indeed, many owners may only seek support from the veterinarian when particular signs are causing a problem for either the dog or themselves. For example, a sudden loss of a previously known behavior (e.g., recall when off lead), house soiling (Figure 2), significantly reduced activity/interaction with the owners, or night-time waking. In these cases, the owner’s focus is on the behavior problem, but it is essential to appreciate that the issue may be more complex due to the potential role of underlying neurodegenerative changes associated with CCD. The importance of thorough history taking during consultations cannot be overstated, as many owners may be unaware of important signs or may not appreciate that they can be addressed, often assuming the changes seen are part of an inevitable aging process. Senior pet health checks and routine appointments (such as for vaccinations) provide an opportunity to actively ask an owner about signs of CCD.

CCD is used as a model for Alzheimer’s disease in people, so it is not surprising that the pathology has been studied extensively 10. Changes noted within the brains of dogs affected by CCD include reduced brain mass, reduced frontal lobe volume, cortical atrophy, reduced neuronal density, increased ventricular size and increased beta-amyloid plaques 7. In humans tau protein fibrils are also noted in Alzheimer’s, but this pathology is more typically found in cats (who coincidentally do not typically show the amyloid plaques found in humans and dogs). Given that the lesions are irreversible and their causal significance not well established, the pathology will not be discussed further here. 

Diagnosis of CCD

CCD is a diagnosis of exclusion, and there are no definitive antemortem diagnostic tests available. A presumptive diagnosis is reached through the information provided by the owner and by ruling out other conditions which could be responsible for the clinical signs 4. Given the presenting signs there are many possible differential diagnoses which need to be excluded (Table 1) and information obtained from the owners is central to the clinical presumptive diagnosis of CCD; to aid this process in terms of speed, consistency and completeness, various screening questionnaires are available 11. Some of these can be completed independently by the owner, such as the canine cognitive dysfunction rating scale (CCDR) 12, which can be given to the owner to complete prior to the appointment and then discussed within the consultation (see Box 1). Others can be completed during the consultation, such as the age-related cognitive and affective disorders score (ARCAD) 13.

In the authors’ experience the CCDR scale is easy to use and can be given to owners to be completed at home if the veterinarian has suspicions of CCD based on the initial information obtained during a consultation (for example, from the history-taking process at a routine booster vaccination). This allows the owner to reflect on their pet’s aging and creates a pathway for engagement in proactive geriatric care.

Given the concerns regarding the under-reporting of CCD, and the potential for subtle but progressive clinical signs, it is recommended owners complete a suitable questionnaire every 6 months for their geriatric dog. This allows early detection of possible CCD and intervention to improve treatment outcomes 12 as it helps distinguish between normal cognitive decline associated with aging and dysfunction.

In addition to the owner history and reported information, the other essential is to check for possible differential diagnoses. The diagnostic tests will depend on the presenting signs for each individual case, and it should be noted that co-morbidity is common. If other differentials have been excluded, a presumptive diagnosis of CCD can be made, but where the picture is obscured by co-occurring conditions with similar signs, clinical judgement must be used, and the uncertainties carefully explained to the client. It is always prudent to review the potential for a diagnosis of CCD whenever a case with related clinical signs does not improve or stabilize as expected, or if there is a sudden deterioration or progression of signs. Likewise, the involvement of unrelated pathologies should be considered in cases of CCD which show a similar pattern of change. For example, if a dog with a diagnosis of CCD fails to improve as expected, this should suggest other factors could be involved, and the case should be re-evaluated for underlying problems such as chronic discomfort which may mimic or contribute to the CCD signs identified.

Common differentials for CCD

There are numerous conditions which have a similar presentation to CCD, and it is important to consider each of these for every suspected CCD case.

Discomfort

Chronic discomfort can mimic many of the signs of CCD, including altered social interactions, sleep/wake cycles, house soiling and activity levels. For example, a dog which has become more withdrawn and less inclined to interact with the owner or other animals in the household may be experiencing osteoarthritic pain and so be reluctant or slow to rise (Figure 3); it may spend more time lying down, or be less willing to interact and play with other dogs in the household, as this may exacerbate the discomfort. In some cases, there may be a sudden onset of aggressive behaviors between the dogs, as the individual experiencing discomfort aims to prevent and repel such interactions. Chronic discomfort can be difficult to recognize, especially if the dog is still able to participate in some normal activities (such as daily exercise, because the immediate motivation to go for a walk overrides any discomfort experienced, at least in the short term). Often these cases may not show overt signs during clinical examination, posing a further diagnostic challenge. In general, if there are suspicions of discomfort, a pain relief trial for a minimum of 4-6 weeks should be used to help evaluate the role of chronic discomfort. It is important to coach the owners that the typical response to the trial will be slow and possibly subtle, and so a behavioral diary can be invaluable to capture these changes. Equally, a gradual deterioration following cessation of the pain relief may be the only reported sign, which would support the suspicion of discomfort. 

Changes in hearing, vision and smell

Loss of hearing, vision and smell can resemble some of the DISHA signs 14. For example, a dog with compromised vision can be reluctant to exercise, or may stay closer to the owners on walks or appear disorientated (Figure 4). A thorough physical examination and history taking specifically related to these areas can be beneficial to assess the role of altered senses. 

Systemic disease

Pathologies affecting many of the major organs can also lead to signs that mimic CCD. For example, reduced activity levels can be caused by dysfunction in the cardiovascular, respiratory, renal or endocrine systems, and the veterinarian must be careful not to approach a case with a preconceived idea as to the cause. If the dog is of the right age, the potential role of CCD alongside these conditions must be considered. Diagnostic tests should be undertaken to rule in or out medical factors which could contribute to the observed signs.

Normal cognitive decline

As part of the normal aging process dogs, like people, will experience a decline in cognition. The questionnaires described above help differentiate cognitive decline from cognitive dysfunction 12. Some dogs will remain in cognitive decline, whereas others will experience signs of dysfunction, hence it is important for the questionnaires to be completed every 6 months, or more often if needed, to help identify signs of dysfunction.

Management and treatment options

Although CCD cannot be cured, early intervention can help slow the progression and improve the quality of life for both the dog and owner 15,16. Management options include medications, nutraceuticals, diet, environmental and behavioral modification. Studies show the most effective combination to be a combination of environmental measures and diet/nutraceuticals 17. Table 2 summarizes common treatments commercially available where there is published evidence of efficacy.

In addition, it is also possible to use symptomatic treatment for specific clinical signs as required. For example, if an animal is struggling with night-time waking despite all other reported signs being well managed with dietary and environmental intervention (and checks have been made to rule out comorbidities) then the following could be considered:

• Setting a nighttime routine to promote a restful state, e.g., walking and feeding in the evenings and closing the curtains to reduce light/noise.
• Medications which may promote sleep, either directly or as a beneficial “side effect” (e.g., chlorphenamine or melatonin).

It is important in such cases for the veterinarian to work closely with the client to discuss the behaviors of concern. As with any chronic condition, owners can find the management and lack of resolution of clinical signs frustrating and upsetting, so an empathetic approach will help. Effective communication regarding treatment options is also key, as the owner needs to be aware the clinical signs are unlikely to completely resolve, but the aim is to reduce the speed of progression and manage specific signs as needed. It is also vital to discuss the potential risks and benefits of each treatment option, especially in light of concurrent health issues which may be present in senior patients.

Pragmatic considerations

Given the reported prevalence of CCD, first-opinion veterinarians are likely to see patients frequently, and the wealth of treatment options can at first appear overwhelming. However, it is important to remember that a combination of treatments will be necessary in order to maximize benefits for the individual patient. An individualistic approach is recommended, tailoring treatment based on the dog’s reported problem(s), as well as wider animal (such as concurrent conditions) and owner factors (such as lifestyle, time and ability to train). The primary aim is to improve the quality of life for patient and client by stabilizing or managing reported signs.

The owner’s autonomy and wishes with regards to assessment and treatment costs must always be respected and accommodated, but that does not mean that owner-related behavior change cannot be encouraged. A pragmatic approach is often necessary, as it may not be appropriate to perform as many diagnostic tests as desired. There may also be reported behaviors which the owner does not feel it is necessary to address, as they do not view them as problematic, or they accept them provided their dog is enjoying a reasonable quality of life. The case studies in Boxes 2 and 3 illustrate some of the challenges that might be involved and appropriate courses of action, and highlight the importance of clinical skills, communication and professional judgement in order to create a bespoke plan, which can be highly rewarding for the veterinarian as well as significantly improving the quality of life for both dog and owner.

Geriatric dogs should be routinely evaluated for signs of CCD 12 and records of their questionnaire score should form part of their routine clinical notes (Figure 5). For dogs showing signs of CCD which are well managed, check-ups every 3 to 6 months may be all that is required, whereas more frequent contact will be required if the signs are progressive or not yet stabilized. For dogs that show persistent signs or a sudden deterioration, it is important to screen for any concurrent health issues which may have developed or progressed since the diagnosis of CCD. For example, if a dog previously showing mild signs of disorientation has suddenly begun to house soil then it is important to check for conditions such as osteoarthritis affecting their ability to toilet outside (e.g., steps to get outside, a considerable distance from resting place to garden, or a slippery floor), renal, liver or endocrine disease (leading to polyuria/polydipsia (PUPD) and possibly a contributing urinary tract infection). 

Conclusion

CCD is a progressive disease, and it can be difficult to predict response to treatment or rate of progression for the condition. Clearly patients with comorbidities have a more guarded prognosis. Owners should be encouraged to monitor the key signs (not just those of initial concern) and be made aware of the level and type of assistance available to help support their pet in order to improve quality of life. Even though outcome can be hard to predict, such an approach ensures the most is being made of the opportunity and many cases will respond favorably, which can be a source of great satisfaction for all involved.