Dog dementia (canine cognitive dysfunction)

Jack, our English cocker spaniel, is seven years old, middle aged for a dog.  He may be a little neurotic, after all he is a spaniel, but he is still sharp as a tack and has no signs yet of cognitive impairment.  It turns out that many mammals do develop cognitive impairment towards the end of their lives. In dogs this cognitive decline is called canine cognitive dysfunction (CCD), and it occurs in up to 60% of dogs over 11 years of age. It is more common in small dogs probably because they tend to live longer than large dogs. As we shall see, it has similarities, and some differences, compared to Alzheimer’s disease in humans.

What does dementia look like in dogs?  Obviously, the type of cognitive tests done in humans are for the most part impossible to use with dogs. The clues to CCD are changes in behavior. The acronym DISHAA(Disorientation, altered social Interactions, altered Sleep–wake cycles, House soiling and loss of other learned behaviors, altered Activity levels and increasing Anxiety) has been proposed as a guide for assessment. A dog with dementia might simply stare into space for long periods of time.  He might sleep during the day and be active at night. She might be unwilling to interact with other pets or even her people. The ability to smell is often decreased, just as it is in humans with Alzheimer’s disease. Several veterinary tests have been developed to grade dog cognition such as the Canine Cognitive Dysfunction Rating Scale (CCDR) comprised of 13 behavioral items evaluating orientation, memory, apathy, impaired olfaction, and locomotion.

Although age-related cognitive dysfunction has been reported in a number of elderly mammals including cats, horses, apes, bears, dolphins and most species of non-human primates, most of the investigations have been done on dogs. The brain pathology in all of these species is very similar to that found in Alzheimer’s disease in humans. Beta-amyloid plaques are found outside of nerve cells in more or less the same parts of the brain across species. Beta-amyloid is also found in the walls of small blood vessels in the brains of humans with Alzheimer’s as well as well as in most of these animals. Abnormal phosphorylated tau protein has been found, but unlike in humans, it does not seem to form into neurofibrillary tangles. Perhaps the non-human animals do not live long enough for tangles to develop. Interestingly, mice and rats do not develop dementia. At least normal, unmanipulated rodents don’t get it. Are you puzzled? Transgenic mice have been the mainstay of building animal models of Alzheimer’s disease.  In a transgenic mouse, human genes for Alzheimer’s are inserted into the mouse genome and then bred into a new strain that regularly gets an Alzheimer’s-like disease. These transgenic mice have been very important models for testing theories and possible interventions for Alzheimer’s disease. But the normal, wild-type mice do not get dementia.

What can be done for a dog with dementia? Is it an unavoidable part of aging? Probably not. Just as some humans live into their 90s without getting Alzheimer’s or other dementias, not all elderly dogs develop canine cognitive dysfunction. Your vet may recommend a special diet, structured activity including regular walks, good daytime sunlight to help maintain a proper sleep cycle, and careful use of certain antidepressants for anxiety.  As in humans, the fewer medications the better. Some studies have found cognitive benefit from acetylcholinesterase inhibitors like donepezil (Aricept), also used in humans, but benefits are subtle and side effects can be an issue.  Don’t use medications except under the guidance of a veterinarian.

Thanks to my friend Dr. Reed Wilson for suggesting this topic.  My primary source for this post was Prpar Mihevc, S. and Majdic, G. Canine Cognitive Dysfunction and Alzheimer’s Disease – Two Facets of the Same Disease? Front. Neurosci. (2019) 13:604.