Cognitive dysfunction is an age-related neurodegenerative disease that impairs memory and learning.
Symptoms and histopathological findings of CDS resemble forms of dementia seen in Alzheimer patients (Dementia Alzheimers Type (DAT)).
CDS can manifest itself in multiple unspecific clinical signs that increase in quantity and severity over time in affected dogs.
Presenting signs
Summary: changes in cell function and neurotransmission in the brain of the CDS patient lead to malfunctions of short term memory, loss of learned behavior, impairment of the processing of sensory information, reduction in cognitive capacity, and alterations of mood. Taken together these create typical patterns of signs that owners recognize.
Progression: the progress of CDS is related to the general rate of aging in the canine. Quite significant changes can occur in the space of weeks or months. Worsening of the condition may be precipitated by stressful events such as hospitalization, kenneling, surgery or a house move. Dogs should be behaviorally assessed before these events.
Emotional changes: mild emotional changes may be the first signs of the onset of dementia. Signs include depression (reduction in activity, play and interest in activities the dog formerly enjoyed). A depressed mood is also a common sign of chronic pain and ill health. Increases in anxiety and fear leading to irritability and aggressiveness.
Defects of short-term memory: the dog repeatedly performs certain actions such as asking for attention, food and other rewards. These behaviors may also be learned as a result of owner reinforcement. Malfunction of short-term memory is at the root of many of the problems seen in CDS.
Disorientation: the dog has trouble recognizing people, locations, or objects. This may lead to secondary problems, such as house soiling and trouble to find locations in the home, eg door to outside, water and food dish.
Changes in sleep-wake cycle: the dog tends to sleep mostly during the day and appears restless at night. Pain and illness are also significant factors in nighttime restlessness in dogs, eg chronic arthritic pain may make rest uncomfortable.
Loss of learned behaviors: failure to respond to commands and social signals that inhibit unwanted behavior. This contributes to loss of social inhibition and alterations in relationships with people and other animals in the home.
Loss of house training (example of a learned behavior) : a previously house trained dog will suddenly urinate and/or defecate inside the house. This symptom can be caused by numerous medical and behavioral problems that have to be ruled out. Once the underlying cause of CDS has been treated the dog may need to be housetrained from scratch.
Changes in interaction with the environment: reduced greeting of the owner, familiar persons or pets,decreased response to commands. A depressed mood and lack of interaction tends to isolate dogs from their owners, who may not instigate play or give attention. Through a loss of stimulation and reward of normal activity the degradation of the human-animal bond leads to social isolation that contributes to worsening signs of CDS.
Neurological: in the latter stages of CDS, neurological impairment may be seen. These include ataxia, apparent sensory loss (loss of vision/hearing) and changes in locomotor reflexes. Dogs can progress to this stage quite rapidly (within a few weeks). Any neurological signs must be investigated thoroughly as there are numerous other potential medical causes.
Age predisposition
The onset of clinical signs is seen in older dogs, depending on individual differences, breed and size.
CDS might occur as early as 7-9 years of age in large size dogs.
Smaller breeds are typically affected later in life (10-12 years of age).
Sex predisposition
CDS occurs equally in neutered male and female dogs.
Circulating testosterone is thought to prevent sexually intact male dogs from progressing from mild to severe cognitive impairment.
The effect of hormonally active tumors (such as affecting the testicle ) is not known, but may be significant.
Breed predisposition
All breeds are equally affected.
Smaller dogs are typically presented at an older age than large or giant breeds of dogs.
More than one quarter of the canines seen in veterinary practices belong to the population of dogs that are at risk to develop CDS (7 years of age or older).
Approximately 60% of 11 year old dogs show signs of CDS.
Avoid changes in the house that may lead to disorientation.
Keep a strict routine to make the environment more predictable.
Increase the number of environmental cues that enable the dog to navigate its environment (audible, odor, tactile), eg use specific cues to identify particular rooms and passages: a continuously playing radio in one room, textured rugs and fragrances in others.
Create a secure bed area that is comfortable and easily located by the dog.
Control dog with a leash in unfamiliar environment.
Avoid slippery surfaces, obstacles and stairs. Use special matting under rugs to make them more stable under foot.
Offer frequent but short walks to stimulating places. Encourage investigation of environment.
Encourage the dog to interact.
Continue the reward based training.
Nutrition:
Senior diets . Prescription diets that supplement antioxidants, eg B/D, Hills® or equivalent antioxidant supplements.
Pharmacological treatment:
Selegiline 0.5-1 mg/kg SID PO. Dopaminergic (monoamine oxidase B inhibitor). Increases exploratory behavior, enhances reinforcement of behavior, improves cognition, reduces apprehension, neuroprotective (reduces apopotosis and induces endogenous antioxidant enzymes). Do not combine with selective serotonin reuptake inhibitor or tricyclic antidepressant.
Propentofylline 3-5 mg/kg BID PO. Increases cerebrovascular blood flow, experimentally this drug is neuroprotective and reduces neurotoxicity of beta-amyloid.
Pheromonotherapy:
Dog Appeasing Pheromone (DAP, CEVA): synthetic analogue is available in an electrically operated diffuser. Reduces anxiety and increases acceptance of environmental stimuli. Potential use in early phase of treatment to reduce anxiety, whilst waiting for effects of diet and medication. It may be useful to install a DAP diffuser when changes in the environment are anticipated, eg in the new home in preparation for a house move. May irritate the respiratory tract of dogs with existing inflammatory upper respiratory tract disease.
Treat all medical problems:
Geriatric animals frequently suffer from multiple problems all of which contribute to the impairment. Successful treatment of CDS demands proper management of all medical problems.
Geriatric animals often benefit more from medical intervention than younger ones and their quality of life is more easily improved.
Review current treatment of existing problems. There is often reluctance to change treatment in older dogs, but their treatment must be re-evaluated regularly.
Review pain management.
Monitoring
Many dogs improve significantly on treatment and can (temporarily) return to a relatively normal level of functioning. The condition is still progressive.
In responsive individuals dietary modification produces some improvement within 4-6 weeks.
Psychoactive drugs such as selegiline produce effects by week 6-8.
It is sometimes hard to appreciate the changes in the dog's behavior because initially these will be subtle. Encourage the owner to keep a daily log of the dog's behavior.
Monitor the dog's progress weekly during the first 2 months. Owners will need support throughout the initiation and maintenance phases of treatment.
Subsequent management
Treatment
Schedule semi-annual geriatric health and medical checks.
Create a program of environmental enrichment to encourage activity in line with the dog's improving cognitive functioning. Use activity feeders, simple reward based training and exposure to interesting environments (short walks to places full of smells and things to investigate). Mental stimulation is essential to improve prognosis.
Ask owners to make a list of the (gentle) games and activities the dog used to enjoy before CDS. Encourage them to actively offer the dog opportunities to do these things so that it may return to its previous pattern of behavior.
Plan a program of reward based training (punishment is absolutely to be avoided) to retrain house-cleanliness and other lost learned behaviors.
Annual medical check-up and geriatric care, starting at 7-10 years of age, depending on the individual's breed and presentation.
Educate owners to notice and mention early signs of CDS (emotional changes, loss of interaction, etc).
Offer a balanced diet, depending on the dog's nutritional needs.
Body weight does not influence the prevalence of CDS signs. But food restricted dogs have a delayed onset of chronic diseases and a significant longer life span. Cognitively impaired dogs of normal bodyweight may be easier to manage than obese ones.
Adequate (age, size, breed) physical exercise and mental stimulation.
Symptoms are typically irreversible and progressive, but this decline can be slowed and some mental function can be temporarily rehabilitated by effective treatment and management.
Early intervention offers the best chance of delaying progression.
The use of neuroprotective drugs and diets combined with a stimulating environment can effectively delay progression so that CDS need not be a lifespan limiting illness.
Veterinary geriatric care, pharmacological intervention, environmental management, and dietary management can help to slower the process and improve quality of life.
Reasons for treatment failure
Owner non-compliance with treatment and management.
Assumption that the behavioral changes are inevitably associated with aging.
Normal progression of the aging process and associated signs.
Landsberg G (2006) Therapeutic options for cognitive decline in senior pets.JAAHA42 , 407-413.
Kealy R D, Lawler D E, Ballam J M et al(2002) Effects of diet restriction on life span and age-related changes in dogs.JAVMA220 , 1315-1350.
Bain M J, Hart B L & Cliff K D et al(2001) Predicting changes associated with age-related cognitive impairment in dogs.JAVMA218 , 1792-1795.
Hart B L (2001) Effects of gonadectomy on subsequent development of age-related impairment in dogs.JAVMA219 , 51-56.
Neilson J C, Hart B L, Cliff K D et al(2001) Prevalence of behavioral changes associated with age-related cognitive impairment in dogs.JAVMA218 , 1787-1791.
Siwat C T, Gruet P, Woehrle F et al(2000) Comparison of the effects of adrafinil, propentofylline, and nicergoline on behavior in aged dogs. Am J Vet Res 61 , 1410-1414.
Other sources of information
Heath S (2002) Behaviour problems of the geriatric pet. In: Horwitz, Mills D, Heath S (eds) BSAVA Manual of Canine and Feline Behavioural Medicine. British Small Animal Veterinary Association.
Vetstream contributor(s)
Jon Bowen BVetMed MRCVS DipAS(CABC), Queen Mother Hospital, Royal Veterinary College, Hawkshead Lane, Potters Bar, Hertfordshire, UK.
Petra A Mertens DrMedVet, FTAV, DiplECVBM-CA, Dipl ACVB , University of Minnesota, College of Veterinary Medicine, 315 Veterinary Teaching Hospital, 1352 Boyd Avenue, St Paul, MN 55108, USA.
A depressed mood is also a common sign of chronic pain and ill health.
Do not combine with selective serotonin reuptake inhibitor or tricyclic antidepressant.