Canine Cognitive Dysfunction

Stewart MacKenzie

2005

Watching the decline of your pet’s physical and/or mental health after years of vitality can be heart wrenching. We often have fond memories of watching Fido playing fetch or watching Fluffy race around the house in apparent glee. The concept of our pet’s senior years has changed drastically. Old dog used to mean Fido was 7-10 years old. Now pets are enjoying active healthy lifestyles well into their early teens, and it is not unheard of dogs living into their mid to late teens, and even early twenties! With the increasing life-span of cats and dogs due to advances in healthcare, and nutrition, new health issues are moving to the forefront in small animal practices everywhere. Where it used to be quite rare to deal with senior pet issues in clinics, there has been a shift in the practical dynamics of clinic work. Increasingly practitioners include senior pet health exams as standard protocols, and the development of strategies to deal with existing issues and in prevention to ensure a better transition for pet and owner into their pet’s senior years. An area of great concern for veterinarian and pet owner alike is the decline in a pet’s cognitive functioning as they get older. Information will be relayed in the following context; what is “canine cognitive dysfunction”, how does it occur, and what are the prescriptive and non-prescriptive things that can be done to help pets in their senior years.

Questions abound when owners first hear a diagnosis of “Canine Cognitive Dysfunction Syndrome” (CDS). The first question usually asked is “Like Alzheimer’s”? The answer is, yes; as dogs age, they can develop a form of neurodegenerative disease that has many similarities with the age relate cognitive disorder Alzheimer’s in humans. More specifically, “like humans, canines naturally accumulate deposits of beta-amyloid (A_B), a type of protein plaque, in the brain with age. Further, canines and humans also share the same A_B sequence that first show as deposits of the longer A_B1–42 species followed by the deposition of A_B1–40. Aged canines like humans also show increased oxidative damage. As a function of age, canines show impaired learning and memory on tasks similar to those used in aged primates and humans. The extent of A_B deposition correlates with the severity of cognitive dysfunction in canines” (Cotman etal 2002). Ultimately the term Canine Cognitive Dysfunction Syndrome is now used to describe the above progressive neurodegenerative disorder in senior dogs. It is generally marked by deficits in learning, memory, perception and awareness.

There are other disorders that can result in some of the same signs and symptoms, also seen in Canine Cognitive Dysfunction. Such disease processes as “metabolic and endocrine disease, to painful conditions such as arthritis or dental disease” (Lansberg 2004) can result in some of the same behaviours as CDS, and it would be advisable to rule out any possibility that these are the root cause. However, specific concerns of: house soiling, disobedience, confusion about previously regular habits, anxious pacing and panting (generalized anxiety) all indicate a primary concern of CDS. Clinically, owners often describe pets with cognitive decline as having, increased anxiety, a decrease in general hygiene and grooming habits, altered appetite, decrease response to stimulus (such as going for a car ride) and problems with learning and memory. These and other symptoms have lead clinicians to adopt the acronym DISHA to describe the following conditions “Disorientation, altered Interactions with people or other pets, Sleep-wake cycle alterations, House-soiling and altered Activity level (Lansberg 2004).

With clear symptoms and signs of CDS, we move to the next step, getting a definitive diagnosis. Although of great clinical value in the diagnosis of CDS (not many clinics have one), a Toronto General Testing Apparatus or TGTA is one way to get a clear cut definitive diagnosis of cognitive impairment. Generally, the TGTA tests an animal’s ability to recognize, remember and choose objects based on similarities and differences, with the resulting proper choice being reinforced with a desired food reward. It has been shown that while young dogs have little problem learning this task, older dogs are unable or have great difficulty in learning to recognize previously reinforced articles. Fortunately, the average clinical practitioner can modify such tasks in the clinical setting, and along with curiosity tests (a basket full of toys, and the dog’s general interest and desire to explore and play with the toys), assign them a level of functioning based on observed outcomes. “Using memory tasks, old dogs can be separated into three groups: unimpaired, impaired and severely impaired” (Lansberg 2004). Assuming there is a definitive diagnosis of CDS, there are many different medically prescriptive and non-prescriptive treatment options available.

The first type of treatment available to the aging dog is in the area of nutrition, or what is commonly known as “dietary therapy”. “Widespread oxidative damage, extensive production of free radicals, and lowered vitamin E levels have all been identified in the brains of dogs with dementia” (Lansberg 2004). It has been widely acknowledged (Milgram et al 2002), that antioxidants, such as vitamins E, C and other factors such as beta carotene, selenium along with mitochondrial co-factors such as L-carnitine, and DL-alpha-lipoic act synergistically to improve antioxidant defence, improve clearance of, reduce production and the effects of free radicals. Free radicals are the toxic result of high rates of oxidative metabolism. Levels of the above vitamins, minerals and co-factors can be improved through the supplementation of fruits and vegetables in the dog’s diet, or by using commercial preparations with these ingredients in them. Interestingly there is also a new canine therapeutic diet available through veterinarians produced by Hill’s Pet Nutrition specifically formulated to treat CDS. Called Canine b/d®, “the diet’s efficacy was assessed using neuropsychological testing procedures for more than 2 years” (Lansberg 2004), and was proven effective in improving performance on a number of cognitive tests.

The second area of treatment available are those that are medically prescriptive. Drugs such as Selegiline and Anipryl ® are MAO (monoamine oxidase) inhibitors. While it is still not clear how these drugs improve dogs with CDS, “enhancement of dopamine and other catecholamines in the cortex and hippocampus is presumed to be an important factor” (Lansberg 2002). Dopamine and Catecholamine levels in the brains of dogs with CDS are significantly low. The use of the drug Anipryl ® has had promising results. Pfizer, the makers of Anipryl ® recommend that the dosage for oral administration for the control of clinical signs associated with CDS is 0.5–1.0 mg/kg once daily, preferably administered in the morning. This is maintained for a month and then the dosage is adjusted accordingly until the desired balance/response is achieved. It needs to be remembered however that there needs to be sufficient amount of time taken to instill a significant noticeable response in the dog.

Ultimately decisions about aging pets are never easy to make. Living with an animal diagnosed with CDS can be heart wrenching and difficult. While there are things that can be done to alleviate some of the symptoms seen in aging pets, conditions may worsen, or new problems due to aging can materialize. There is a wide choice of treatments available to clients willing to spend the time to find the right balance in treating their pet. It needs to be remembered that a dog’s apparent misbehaviour is probably not intentional, but an effect of his condition. While it is always desired that pets live full happy lives, with greater longevity, cognitive dysfunction in aging pets will be increasingly seen in clinics and by more practitioners. All involved need to be aware of the options available to them in treating this disorder.

References:

Cotman, C. W. et al. 2002. Brain Aging in the Canine: a Diet Enriched in Antioxidants

Reduces Cognitive Dysfunction. Neurobiology of Aging 23: 809–818

Borra’s, D., Ferrer I., and Pumarola, M. 1999. Age-related Changes in the Brain of the Dog. Vet Pathol 36:202–211.

Dimakopoulos, A. C. and Mayer, R.J. 2001. Aspects of Neurodegeneration in the Canine Brain. Waltham International Symposium: Pet Nutrition Coming of Age.

Lansberg, G. 2005. Therapeutic Agents for the Treatment of Cognitive Dysfunction Syndrome in Senior Dogs. Progress in Neuro-Psychopharmacology and Biological Psychiatry 29: 471-479.

Milgram, N.W. et al. 2002 Landmark Discrimination Learning in the Dog: Effects of Age,

and Antioxidant Fortified Food, and Cognitive Strategy. Neuroscience and Biobehavioral Reviews 26: 679–695.

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