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Cognitive Dysfunction in Elderly Dogs

By: Dr. Nicholas Dodman

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As veterinary medicine has become more sophisticated, and careful nurturing of pets has become the rule rather than the exception, the population of geriatric small animal pets has grown steadily, mirroring the increase in the human elderly population. As an animal progresses into its twilight years, inevitable aging changes take place in all organ systems, including the brain.

Most small to medium-sized dogs are considered geriatric when they reach 10 years of age, or when 75 percent of their anticipated life span has elapsed. But this does not mean that when they have exceeded this arbitrary limit they will necessarily show signs of senile dementia. Some dogs appear normal mentally long after the empirical cutoff, and some remain bright to the end of their natural life span. These lucky dogs are referred to as "successful agers," same as their human counterparts. Dogs that do not weather aging so well, and who show obvious signs of mental deterioration, constitute unsuccessful agers.

The Signs

Though variable in degree and expression, the classical signs of cognitive dysfunction (CD) in elderly dogs include:

  • Reduced activity
  • Increased sleeping
  • Reduced responsiveness to commands/apparent deafness
  • Lack of interest in surroundings/events
  • Confusion/disorientation
  • Inability to recognize familiar people
  • Increased thirst
  • Excessive panting
  • Difficulty eating and/or reduced interest in food
  • Loss of bladder and bowel control
  • Difficulty navigating the environment (e.g. stairs)

    Not all dogs show all of these signs and some will show paradoxical behaviors, such as agitation and/or barking, for no particular reason. However, the signs of CD are progressive and eventually will completely incapacitate the dog. It is interesting to note that the percentage of dogs affected with CD at 10 years old, 12 years old, 14 years old, mirrors the age-related demographic for cognitive dysfunction in humans.

    Central Nervous System

    Though not identical to the changes in human Alzheimer patients, pathological changes in the brains of dogs with CD are similar to those in human Alzheimer's patients and are proportionate to the severity of the clinical syndrome. Many different changes have been reported but the most significant are deposits of beta-amyloid and its formation of plaques in the brain. It is these pathologic changes, and their functional sequelae, that are thought to be responsible for the cognitive/behavioral deterioration associated with CD.

    The Cause

    Pathological changes in the brains of affected animals are directly responsible for signs of CD but why should such changes occur in one animal and not another? Although we don't know the precise reason for individual susceptibility, inheritance probably plays a role. But some interaction between genetics and the environment cannot be dismissed as also contributing.

    Treatment

    There was no treatment for this degenerative condition until the advent of deprenyl. (Anipryl®) This drug helps turn back the aging clock and buy affected dogs more quality time. Deprenyl is not a primary treatment for the disease process but will symptomatically reverse the clinical signs of aging in most dogs with CD by increasing brain concentrations of the neurotransmitter dopamine. Dopamine "connects thought with action" and also increases cognitive awareness. In the Oliver Sack's movie, Awakenings, patients were unable to move because of the lack of dopamine. Dopamine is low in human Parkinson's patients, who have difficulty moving around. In contrast, excessive dopamine levels produce racing thoughts, paranoia, increased anxiety, and repetitive behaviors. If the canine aging theory is correct, CD patients have low dopamine, hence low activity and reduced cognitive performance. Increasing dopamine by means of deprenyl should, and does, reverse the clinical signs of CD in the majority of patients – for a time at least.

    One third of canine CD patients respond extremely well to treatment with deprenyl by regaining their youthful vigor; another one third respond reasonably well; and one third do not respond at all (perhaps there is a variant of CD with different neuropathology). The bottom line is that for any dog that is slowing down to the point that problems become apparent, treatment with deprenyl is the logical choice once other organic causes for reduced mental function have been ruled out.

    Many people think that it is "normal" for their elderly dogs to gradually lose energy and interest in life. They therefore tolerate the cognitive aging syndrome for longer than is necessary. These folks sometimes don't seek help or wait until bladder or bowel control is lost before trying to find out if something can be done. The latter is the main cause for concern for owners of geriatric dogs, who seem to be able to put up with almost any amount of senile change in their pets before the indignity of incontinence finally causes them to seek help. Incidentally, it's often the same for human Alzheimer patients.

    Deprenyl is marketed with the specific label instruction for the treatment of age-related cognitive dysfunction and age-related inappropriate urination. Early treatment with the drug will buy impaired dogs extra quality time increasing their "health span." As a side effect, deprenyl also increases the life span of dogs over 10 years – and that's nothing to sniff at.

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