A year ago, Karen and Jim Silsby’s miniature schnauzer began to act strangely. Hannah, then 13, got lost in the yard she had once known so well, started sleeping excessively, got stuck behind furniture, developed a clouded recognition of her surroundings, became less housebroken and started barking despite being a quiet dog most of her life.
A visit to veterinarian Tom Rose of Rolling Hills Veterinary Clinic in Columbia revealed that Hannah had dementia. She is among the 60 percent of dogs ages 11 to 15 who have symptoms of dementia, according to ScienCentral, a production company specializing in science and technology content for television and the Internet. Dementia is the umbrella term that refers to the loss of higher brain function, according to Dennis O’Brien, an MU professor of veterinarian neurology.
“Dementia refers to clinical signs and the exhibition of symptoms,” he said. “It’s like saying someone has a cough because he has a cold or because of lung cancer. Alzheimer’s disease, for example, is a specific disease entity, which includes symptoms and specific changes in the brain.”
The behavioral changes in dogs with dementia, also known as canine cognitive dysfunction, parallel the behavioral changes in humans with Alzheimer’s disease. Both aged humans and aged dogs experience changes in learned habits such as loss of personal care, grooming, health and a disruption in sleep cycles, said Debra Horwitz, an MU adjunct professor and St. Louis veterinarian who has a private practice specializing in animal behavior.
Although a number of animals, including cats and primates, can suffer from dementia and age-related ailments, dogs are the species most often studied, O’Brien said.
Aged humans and dogs share similar brain pathology or brain characteristics. For example, research reveals that humans and dogs with dementia lose neurons, the brain cell clusters that control thinking, learning and memory that are responsible for receiving sensory data.
Research also demonstrates that the brains of humans and dogs with dementia have amyloid plaques or proteins, an abnormal structure especially found in areas central to memory functions. “(The) dog has been used as a model in brain aging for humans because dogs get amyloid plaques,” said Horwitz. “Amyloid plaques in dogs are similar to the plaque deposits in humans with dementia of the Alzheimer’s type.”
But unlike humans with advanced Alzheimer’s disease, dogs do not develop a second abnormal structure, that of neurofibrillary tangles. Gayle Johnson, an MU veterinarian researcher and director of the veterinary lab, receives samples of tissues to study from animals, including dogs, from across Missouri.
“In a series of dogs which were older and younger, we looked for the presence of amyloid plaques,” she said. Johnson said plaques were more prominent in dogs that were advanced in age. Unlike carnivores, animals that only eat plants, such as horses, mules and donkeys, lack these amyloid plaques.
A major debate in dog dementia research is whether the accumulation of amyloid plaques correlates with behavioral changes and cognitive decline in dogs.
“Are the amyloid plaques developing and then the neurons dying or are neurons dying and then the amyloid plaques developing?” Horwitz said. “The cause of cognitive dysfunction is not clear.”
In humans, there is no such debate. “It’s pretty well-established that plaques and tangles represent dementia and the amount of cognitive and behavioral changes associated with Alzheimer’s disease,” said James R. Slaughter, an associate professor of neurology, psychiatry and family and community medicine at MU. “The greater the number of plaques and tangles in the brains of patients, usually the more severe the dementia and behavioral problems in humans.”
Although researchers have studied dementia in mice, O’Brien said, those studies have failed to offer much insight into the effects of dementia on the human population. That’s because most lab mice are bred specifically for lab use, Johnson said. “Mouse strains are bred to the point where they are genetically one creature,” she said. “The advantage in knowing they are genetically homogenous is that it will allow the effects of experimental procedures to become more obvious.”
But a population that is genetically one and the same does not help in understanding how a condition like dementia develops, Johnson said. O’Brien said that dementia affects each human differently, so studying dogs is a better option than mice.
“There is more variability to what happens in a person clinically as opposed to a mouse in the lab,” O’Brien said.
Practical reasons also support research of dementia in dogs. Dogs have moderate life spans of 12 to 20 years, are easy to handle, share a common environment with humans, sometimes eat similar foods and are a viable population.
O’Brien said more research on canine dementia is needed before scientists and veterinarians understand the specific types of dementia dogs develop. For example, although both humans and dogs can experience Alzheimer’s-like symptoms, researchers would not classify the dog’s dementia as that of the Alzheimer’s type, O’Brien said.
Complicating factors such as other diseases and ailments may be the source of the behavioral problems in dogs, Johnson said.
Rose, the Columbia veterinarian, said that identifying dementia in dogs is a “diagnosis of exclusion.” That is, the veterinarian rules out other possible causes for the dementia. For example, kidney disease or arthritis may cause dementia-like symptoms in dogs.