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Veterinarian Technician November 2009 (Vol 30, No 11)

Peer Reviewed — Care in the Golden Years: Understanding Canine Cognitive Dysfunction

by Kristen White, CVT, Lisa Garrison

    Canine cognitive dysfunction syndrome (CDS) is a neurodegenerative disorder in senior pets that is characterized by increased brain pathology and cognitive decline. Aging affects all the body's systems and can directly or indirectly affect behavior. Physical manifestations of aging in dogs are progressive and generally irreversible. When the clinical changes are mild, pet owners tend to neglect them or to regard them as normal functions of the aging process.1

    The brains of senior dogs have been found to have neuropathologic lesions similar to those in humans diagnosed with dementia,2 such as cerebrocortical and basal ganglia atrophy, an increase in ventricular size, widening of the sulci, narrowing and retraction of the gyri, leptomeningeal thickening in the cerebral hemisphere (although not in the cerebellum), meningeal calcification, demyelination, an increase in the size and number of glial cells, and a reduction in neurons.3

    Antioxidant mechanisms that protect against oxidative damage can be overwhelmed in the brains of senior dogs, which can lead to cellular damage and increased production of β-amyloid, a neurotoxic peptide that is the main constituent of amyloid plaques found in the brains of humans with Alzheimer's disease.1 Studies show that greater β-amyloid accumulation corresponds with greater cognitive impairment.4

    The brain is also susceptible to the effect of reactive oxygen species, known as free radicals. Free radicals originate primarily during mitochondrial aerobic metabolism, particularly during electron transport and respiration in aged mitochondria.5 Free radicals have been associated with mutations in DNA, damage to lipids and protein, and physiologic decline of cellular function.

    The diagnosis of CDS begins with a complete physical examination by the veterinarian. The examination should include appropriate laboratory tests to rule out any underlying metabolic problems that may be treatable, such as hypertension, diabetes, Cushing's disease, and thyroid disease.2 Recommended tests include a CBC, urinalysis, a serum biochemistry profile, and endocrine screening tests. Additional diagnostics, such as radiography, fecal testing, organ function tests, water intake measurement, and ultrasonography, may also be performed to rule out underlying problems.6

    Once underlying medical problems have been ruled out or controlled, the next step in addressing a behavioral problem is to obtain a complete behavioral history from the owner.2 Each clinic typically has a behavioral history form on file, and many veterinary organizations offer free samples or guidelines for creating an appropriate form.

    The aging process does not affect all cognitive abilities equally, and some signs may not be present on examination. Age-impaired dogs may have trouble completing certain discrimination tests, lack curiosity around novel objects, or display impairment during memory testing.3 In addition to clinicians obtaining a behavior history, they can perform several neuropsychologic tests that rely on quantitative measurement rather than subjective behavioral health questionnaires. The Toronto General Testing Apparatus (TGTA) is designed to assess a dog's ability to recall objects based on similarities and differences, using a food reward when the dog selects the correct object. The TGTA is typically used in research settings because it requires a great deal of time to test the animal and the device is cost-prohibitive for general practitioners.3

    A curiosity test has proven more suitable for use in private practice. The curiosity test requires approximately 10 minutes, and a selection of dog toys, to evaluate the amount of exploratory behavior that a dog exhibits. These tests classify geriatric dogs as unimpaired, impaired, or severely impaired.3 Memory function studies in geriatric dogs have shown that impaired animals cannot recall an object after encountering it five to 10 times.3

    The acronym DISHA (disorientation, interaction alterations, sleep-wake cycle alterations, housesoiling, and activity changes) is used to describe clinical signs of CDS.3 In addition, numerous other signs of CDS have been reported, including spatial disorientation, altered learning and memory, increased or decreased activity, altered social relationships, increased restlessness or anxiety, change in appetite, excessive vocalization, and decreased perception or responsiveness.

    A recent study concluded that 62% of dogs 11 to 16 years of age demonstrated at least one behavioral change associated with CDS.2 The study also demonstrated that the increase in signs was directly correlated with the increase in the age of the dog. Veterinarians surveyed for the study reported that 7% of clients with dogs aged 11 to 16 years reported behavioral changes in their pet without being prompted.2 This study demonstrates the benefit of administering a behavioral questionnaire to owners of senior dogs at each wellness examination to allow early diagnosis, intervention, and treatment.

    Treatment Options

    Several treatment options are available for managing CDS.

    s-Adenosylmethionine (SAMe) is a nutraceutical that has primarily been studied for its antidepressant effects in humans. In veterinary medicine, it has been used in cases of liver disease but has now been found to effectively treat cognitive decline in animals.9 SAMe does not appear to have any adverse interactions with other medications, so it can be used as an adjunctive therapy.6

    Nutritional and dietary supplements are also used in treating CDS. Antioxidants (e.g., vitamin E) and mitochondrial cofactors (e.g., lipoic acid and fatty acids) work together to slow damage of free radicals and protect cell membranes.4 Some prescription diets also contain antioxidants, lipoic acid, carnitine, omega-3 fatty acids, and other nutrients to combat brain aging and age-related behavioral changes.9

    Behavioral and environmental modification may also be necessary.2 For example, if a dog exhibits inappropriate soiling, the owner may have to accompany it outside and provide positive reinforcement—similar to housebreaking a puppy. Confinement is a type of environmental modification that keeps the dog out of certain areas of the house that may be targets of inappropriate soiling.

    Environmental enrichment is important for senior dogs. Food puzzles and obedience refresher courses are a form of valuable mental stimulation. If a dog is physically able, it can be beneficial to provide lengthy, daily walks as well.

    * * *

    Through early diagnosis and intervention, CDS in senior dogs can be better managed. By educating clients about this illness, including its signs and treatment options, technicians can help to preserve the human-animal bond.

    1. Bowen J, Heath S. Behavior Problems in Small Animals: Practical Advice for the Veterinary Team. Philadelphia: Elsevier; 2005.

    2. Horwitz DF. Behavior problems in senior dogs. Proc ACVC 2001.

    3. Landsberg G, Hunthausen W, Ackerman L. Handbook of Behavior Problems of the Dog and Cat. 2nd ed. Philadelphia: Saunders; 2003.

    4. Hoskins JD. Geriatrics & Gerontology of the Dog and Cat. Philadelphia: Elsevier Health Sciences; 2004.

    5. Ikeda-Douglas C, Zicker S, Estrada J, et al. Prior experience, antioxidants, and mitochondrial cofactors improve cognitive function in aged beagles. Vet Ther 2004;5(1):5-16.

    6. Landsberg GM, Hunthasuen W, Ackerman L. The effects of aging on the behavior of senior pets. In: Handbook of Behavior Problems of the Dog and Cat. 2nd ed. Philadelphia: Saunders; 2003:269-304.

    7. Manufacturer's information. Pfizer Animal Health. Accessed March 2009 at http://www.cdsindogs.com/PDF/CDSInDogs/ANIPRYL.pdf.

    8. Pfizer Animal Health. CDSindogs.com. Accessed Oct. 2009.

    9. Cotman C, Head E, Muggenburg B, et al. Brain aging in the canine: a diet enriched in antioxidants reduces cognitive dysfunction. Neurobiol Aging. 2002;23(5):809-818.

    References »

    NEXT: Peer Reviewed — Perioperative Hypotension

    didyouknow

    Did you know... According to the American Animal Hospital Association (AAHA), only about 14% of senior animals undergo regular health screenings as recommended by their veterinarians.Read More

    These Care Guides are written to help your clients understand common conditions. They are formatted to print and give to your clients for their information.

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