One of the saddest things I've ever seen was an acquaintance of mine scolding her aged dog because he had peed on the floor. She assumed that he was "mad" at her for leaving him for the day, and that peeing on the floor was his way of getting even. What she didn't know is that behavioral changes in elderly dogs are often caused by physical and neurological changes, and that when they do something "bad" like have an accident in the house, it is rarely by choice and is likely even more distressing to them than it is to their owner. You can expect behavioral changes in older dogs, and if these behaviors are troublesome, often a vet or behaviorist can help.
Aging brings with it many physical changes for dogs: skin and hair disorders and changes, including the distinctive greying of the muzzle; reproductive system changes, especially for male dogs (male dogs who have not been neutered often develop prostate problems; there is no canine menopause); bone and joint problems, including osteoarthritis; muscular atrophy; decrease in heart, lung, liver, and kidney function; intestinal issues (constipation, gastritis); weakened immune system; vision changes and hearing loss.
Aging also affects the canine brain, and just like humans, dogs experience cognitive declines as they age. They can even develop dementia, which is often referred to as cognitive dysfunction syndrome (or CDS). The brains of dogs with senile dementia are more or less identical to those seen in cases of human Alzheimer's disease. Like Alzheimer's, CDS is not curable, but drug treatments (such as Anipryl) have been shown to help slow a dog's decline and can sometimes decrease symptoms.
Changes in the brain can affect behavior. Dogs with mental deterioration may stop being as interested in their owners, sleep more, become incontinent or disoriented, and show changes in personality. Sometimes the behavioral changes are subtle, and pet owners often don't notice symptoms, or don't report them to their vet, assuming they are normal signs of aging. Veterinarian David Taylor, author of Old Dog, New Tricks, mentions a few of the most common behavioral changes seen in older dogs, along with their likely physiological cause: dental disease-suffered by the majority of old dogs, can cause pain, thus irritability; loose stools can cause house soiling; less efficient lungs reduce oxygen levels, leading to decreased energy, a tendency toward confusion during the night, and senility; heart disease restricts a dog's ability to exercise, and leads to more sleeping during the day (all dogs over 13 have some degree of heart disease, he says); inefficient processing of waste by the liver can contribute to cognitive dysfunction; kidney disease can cause excess urine production, which can sometimes lead to urinary accidents in the house; enlarged prostate can lead to incontinence; an underactive pituitary can lead to increased irritability, overeating, excessive drinking, restlessness, and house soiling; loss of bone density and muscle mass may decrease mobility; and failing senses can lead to increased vocalization, fear, and aggression.
One of the most common behavioral issues for older animals is anxiety, my dog Ody's favorite neurosis (and a bugaboo for many humans, too). Taylor says of anxiety in old dogs: "Although they are experienced in life and set in their ways, old dogs often exhibit signs of anxiety that can involve problem behavior. They can become more irritated by or fearful of changes in their environment..." Anxiety can often be related to physical infirmities. For example, a dog whose body is producing an excessive quantity of urine may be anxious about soiling the house. Also, the loss of sight and hearing can create feelings of anxiety, as can cognitive dysfunction. "Some elderly canine behaviors," Taylor writes, "are expressions of a conservative, averse-to-change attitude which is similar to that commonly seen in old people." Ody is most certainly anxious about his physical changes, particularly the refusal of his hind end to behave as it should. I can see worry in his face as he sways and limps and struggles to stand upright enough to eat.
Taylor believes that many of the problematic behaviors related to aging can be addressed by a committed pet owner. Perhaps the most important point is this: behavioral problems such as urinating in the house oftentimes stem from a medical condition, and the vet is the first person to see, not the behaviorist (who might be second). The first person to see is definitely not the euthanasia specialist, or the shelter in-take worker. If we anticipate behavioral changes as our animal ages, we can remain proactive in seeking their root cause and helping our animal adapt to aging. We'll also be far more likely to successfully adapt ourselves.