While true mental illness in dogs is rather rare, it's something I've inadvertently encountered quite a bit and had to learn how to recognize and work with. I've worked with dogs with genetic anxiety disorders, I've encountered dogs with OCD, PTSD, Trichotillomania, and I even once encountered a dog that suffered from hallucinations.
Note: If you have a dog with a mental disorder while medication can be an amazing resource to helping your dog overcome the issue, medication alone is NOT enough to treat the problem. There is still a lot of training and behavior modification (positive training methods are essential in these cases) that will be required to help your dog become a balanced, happy companion.
Signs to look for for Mental Illness in dogs:
Canine Obsessive Compulsive Disorder (OCD):
While your dog might "go crazy" for the frisbee, tennis ball, or laser pointer, this is very different from being obsessed with it (although frisbees, tennis balls, and laser pointers can all be triggers for obsessive compulsive behaviors). A dog with OCD will engage in a behavior or activity for hours on end. This can be anything from rolling a ball around in a specific way, chasing their tail, shadow or light chasing, and more. It can sometimes be very difficult to get the dog to disengage from the behavior. If you are able to get the dog to disengage from the behavior the dog will usually go right back to doing it again as soon as he is left to his own devises. Often times trying to distract or stop the dog from engaging in the behavior can cause the dog to become upset, distressed, or even aggressive. Medication will be required as part of the protocol for behavior modification with dogs suffering from Canine Obsessive Compulsive Disorder.
This is an OCD related behavior that usually involves the obsessive grooming or scratching of oneself to the point of causing bodily harm. This may involve your dog obsessively licking her feet, tail, or legs to the point of them becoming raw and/or bloody, scratching at a specific place to the point of injuring herself, constantly rubbing along something causing hair loss, rashes, or cuts, etc. Medication is often required as part of the protocol for behavior modification with dogs suffering from Trichotillomania.
While basic depression in dogs can usually be resolved simply by increasing interaction, attention, and activity, a Depression Disorder is much more difficult to fix. The dog will often be lethargic, listless, and completely uninterested in his surroundings. The dog will have little to no interest in doing things he normally loves. Sometimes the dog may even lose interest in food and water, causing the dog to potentially become malnourished and dehydrated. Many owners will often think their dog is suffering from some sort of physical illness when the dog is actually struggling with Depression. Medication will be required as part of the protocol for behavior modification with dogs suffering from Depression.
Genetic Anxiety Disorder:
This is far more than just your run of the mill basic fears or anxiety in dogs which are usually caused from lack of socialization, lack of training, or a traumatic experience. This is anxiety caused from a chemical imbalance going on in the brain. Much of the time it is displayed as fear aggression, but not always. Most commonly there will be seemingly no trigger to cause the anxiety. It seems to just sort of crop up out of nowhere. At first you will find a lot of inconsistencies with the dog's fears. One day the dog will be afraid of something and the next day the dog is fine with it, or one day something that the dog loves the next day produces extreme fear. As the dog gets older these fears will usually settle onto one specific thing or things. You may find that sometimes these fears may even trigger what appear to be panic attacks. In my experience it is most commonly a fear of strangers or anything new. You will find that no amount of training and no training method seems to work to get the dog over the fear. The dog will constantly be in a state of taking 2 steps forward then 10 steps back. While an anxiety disorder can happen with any breed in my experience it is most commonly found in herding breeds, Australian Cattle Dogs or "Heelers" in particular. Medication will be required as part of the protocol for behavior modification with dogs suffering from a Genetic Anxiety Disorder.
Phobias are a form of anxiety and are far more than just a basic "fear" of something. This is when the fears become so severe that they become debilitating or even dangerous. Dogs will often try to hide while the Phobia "trigger" is present and may even become aggressive if you try to get them to stop hiding. They will become suspicious of anything similar to or resembling the original Phobia and will often times become afraid of more and more things. Dogs exhibiting a Phobia of something have been know to do extremely dangerous things, such as running out into traffic or even jumping from a 3rd story window, in order to escape the fear. Thunder and fireworks tend to be the most common causes of Canine Phobias however a dog may develop a Phobia towards just about anything. In many cases Phobias can be overcome without the use of medication using the proper behavior modification protocols, however, in cases in which the dog is displaying dangerous behaviors in order to escape the Phobia trigger medication is highly recommended.
Canine Post Traumatic Stress Disorder (PTSD):
This is another form of anxiety that is brought on by a traumatic experience. It is being discovered that many dogs coming out of police or military work are coming back with PTSD. Dogs coming from extremely abusive situations may also exhibit PTSD. Whatever the trigger that causes the PTSD you will find that the dog will develop a specific set of fears or phobias towards a specific thing(s). Some triggers may even cause what appear to be "flash backs" and panic attacks. Dogs with PTSD will usually exhibit a lot of the same symptoms as dogs with Genetic Anxiety Disorders or Phobias. In many cases Canine PTSD can be overcome without the use of medication using the proper behavior modification protocols, however, in many cases medication may be found necessary to help the dog cope and fully overcome the issue.
A Final Word:
As more and more information comes out in the field of Canine Mental Illness it is something that I definitely try to study and keep up on. If you'd like to learn more for yourself, here are some great articles on animal mental illness:
What Animal Mental Illness Tells Us About Humans
Pets with Mental Illness