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Is Your Dog Senile?

By: Dr. Nicholas Dodman

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There is nothing unusual about growing old. It happens to the best of us. Nevertheless, most of us don't enjoy watching the aging process occur in ourselves and in our loved ones. And similarly, we don't like to see our pets grow old.

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 advances into the twilight years, inevitable aging changes take place in all organ systems, including the brain.

Dogs are considered geriatric when they reach 10 years of age, or when 75 percent of their anticipated life span has elapsed. This does not mean that when they have exceeded this arbitrary limit they will automatically show signs of senile dementia. Some dogs appear normal cognitively long after the empirical cutoff, and some remain bright to the end of their life span. Such dogs are referred to as "successful agers," same as their human counterparts. Dogs that do not weather the aging process well and who show obvious signs of mental deterioration constitute the 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 also show paradoxical behavior, such as agitation and/or barking for no particular reason. The clinical signs of CD are progressive and will eventually incapacitate the dog. It is interesting to note that the percentage of dogs affected at 10 years old, 12 years old, or 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's disease, the changes in the brains of dogs with CD are similar to those in Alzheimer's and are found in proportion to the severity of the clinical syndrome. Many different neurological changes have been reported in canine brains, the most significant of which are deposits of beta-amyloid and its formation of plaques. These pathologic changes are thought to be responsible for the observed cognitive/behavioral deterioration.

    The Cause

    Changes in the brain may be responsible for CD but we don't know why they occur. Genetics probably play some role. However, an interaction between genetics and the environment cannot be dismissed, and management factors, such as excessive vaccination and environmental stress may also be part-responsible.


    There was no treatment for this degenerative condition until the advent of deprenyl (Anipryl®), a drug that has helped turn back the aging clock and buy affected dogs more quality time. Deprenyl is not a primary cure but reverses the clinical signs of aging by increasing brain concentrations of the neurotransmitter dopamine. Dopamine is a neurotransmitter that connects thought with action and increases cognitive awareness. In the Oliver Sack's movie, Awakenings, patients could not move because of the lack of dopamine. Dopamine is low in Parkinson's disease, a condition in which patients have difficulty moving, and who also eventually have cognitive impairment. 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 cognitive performance. Increasing dopamine by means of deprenyl reverses signs of CD in a good number of canine CD sufferers. One third of affected dogs respond extremely well to treatment with deprenyl, 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 route once other organic causes for reduced mental function have been ruled out.

    Many people think that it is "normal" for their elderly dogs to lose energy and interest in life and tolerate the cognitive aging syndrome far longer than necessary. These folk either don't seek help or wait until bladder or bowel control is gone before seeking an opinion. The latter is the main cause for concern for owners of geriatric dogs, who can tolerate almost any amount of senile change in their pets before the indignity of incontinence finally causes them to seek help.

    Deprenyl is marketed with the specific label instruction for the treatment of age-related cognitive dysfunction and age-related inappropriate urination and 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.

    A new method for the prevention and/or treatment of CD in dogs is a dietary one. Hills Petfood has introduced a prescription diet called Hills BD (brain diet). The diet is rich in antioxidants and slows the progressions of CD by inhibiting the physical damage caused by the accumulation of "free-radicals" in susceptible dogs aging brains. Furthermore, this dietary treatment may also help reverse signs of CD in some affected dogs.

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