Dementia in dogs is properly called canine cognitive dysfunction syndrome (CDS). It is seen in dogs over ten years old and is similar to dementia in elderly people. According to The Whole Dog Journal, treatment is possible through diet changes, monitoring the dog more closely and the use of a drug called Anipryl.
Accidents In the House
The Veterinarians' Guide to Your Dog's Symptoms claims that suddenly soiling in the house after years of no accidents is usually the first sign of dementia and other illnesses.
The dog will often seem to not recognise people or dogs he has known for years. She may also get stuck in room corners, not realising that all she has to do is back out.
Changes in Circadian Rhythm
The dog will also seem confused about when day and night is. He may sleep all day and then pace all night, waking everyone up and expecting to be fed breakfast.
The dog may often aimlessly walk in small circles or stare off into the distance for hours. She may also be unable to find her way home from familiar places.
Changes In Appetite
The Whole Dog Journal notes that often (but not always) a dog's appetite will suddenly increase or decrease.