6 common medical problems that can masquerade as bad behaviour in your cat or dog

A veterinary behaviourist on the sudden changes that might indicate an underlying problem with your pet.

A veterinary behaviourist on the sudden changes that might indicate an underlying problem with your pet

(Credit: iStock/Getty Images)

There are many dog and cat owners dealing with behaviour issues in their pets that seemingly never get better, writing off their pet as being untrainable or a lost cause. But they, and you, may be surprised to learn that there could actually be another culprit to blame for those truly stubborn behaviour problems, namely an underlying health issue. 

Here, Dr. Karen van Haaften, a veterinary behaviourist at the BC SPCA, lends her expertise on the most common medical conditions behind behaviour problems, and shares what warning signs to look for in your dogs and cats.   


Van Haaften explains that underlying pain is responsible for a huge number of aggression cases and is quite easy to overlook. "There often aren't a lot of outward signs because [your pets] try to hide the pain behaviourally," she explains. "The theory is that evolutionally, it's not a good idea to broadcast weakness." Although this tendency to hide pain is more prevalent in cats, van Haaften notes it can be a real barrier to getting to the root of a behaviour issue in dogs as well.  

If your pet's pain comes on suddenly, then their aggression likely will, too. If, for example, your dog recently fell down the stairs, but seemed fine, and is now all of a sudden growling when you go near its back leg, then that might be something to mention to a vet. If your pet was previously comfortable with most types of handling and suddenly shies away from touch or becomes aggressive when touched, this can be a big red flag. Pay attention to whether or not the aggressive response is specific to a certain area of the body to figure out where the injury might be.

It's easy to overlook or explain away more subtle signs of pain in the body. If your dog suddenly doesn't want to jump on the couch, into the car or walk up the stairs, or if your cat suddenly doesn't want to climb in or out of the litter box or up to its usual spots, it might be time for a checkup.

Van Haaften adds that it can be harder to identify chronic pain or pain that has slowly escalated over time. So be mindful if your dog or cat is aging, has arthritis or has had previous injuries.

Lower urinary tract and systemic issues

Nothing drives people crazier than when their cat or dog all of a sudden starts using the living room carpet as its own personal toilet. "People often assume that inappropriate urination is something animals do out of spite," says van Haaften. In fact, this could be a sign that your pet has a systemic issue or that something's wrong in their urinary tract. 

Watch out for your dog suddenly eliminating in weird spots, like urinating indoors as opposed to the spot it's always used outside. If the issue is in the lower urinary tract, your pet might have difficulty urinating — you might even see them straining to complete or whining and vocalizing during a potty break. If it's a systemic issue, such as diabetes, hyperthyroidism or renal failure, then the volume of urine will increase markedly; your pet might urinate for a much longer time or have to go outside more often. Any of these sudden behaviours is worth investigating with your vet.

Iatrogenic diseases

If an illness or symptom is "iatrogenic," that means that it has been brought on as a side effect from a certain medication or procedure. For many pets that are on medication, the side effects can show up as confusing behaviour problems. As van Haaften explains, "a certain behaviour might not be normal for that dog, but it would be normal if that dog was on a certain medication." 

According to van Haaften, the most common iatrogenic symptom that shows up in dogs is aggression or irritability. For example, "prednisone, which is a steroid, has been known to cause sharp increases in behavioural aggression and also an increase in thirst, since the urine becomes less concentrated and more water is lost through elimination." It's best to educate yourself about all the possible side effects of any of your pet's medications before you begin treatment.

Dermatological issues

When your dog or cat has an issue with its skin, it can be almost unbearable; the frustration and endless discomfort can make even the sweetest pet woefully unhappy. But because the behaviours associated with this type of problem are more of a burden to the pet than the owner, they're easy for us to overlook or ignore. 

So watch out for things like itching, sensitivity to touch and over-grooming. Van Haaften cites one study that found an underlying medical causes in 76 per cent of cat cases which were suspected of psychogenic alopecia — psychologically motivated, compulsive over-grooming. "True 'psychogenic' alopecia is actually a very uncommon diagnosis in cats," van Haaften says.

Gastrointestinal issues

Gastrointestinal issues are really common. We probably all know someone whose dog got into the garbage or ate a plate of brownies and then spent the next two days making a mess of the house. "Obvious signs of these issues are vomiting, diarrhea or weight loss," says van Haaften. However, these issues can also cause a lot of really weird oral behaviours. 

Dogs will often spend a good few hours licking the walls, the floor, the couch or anything that they can find when they have an upset stomach, while cats can develop "pica," which basically means they want to eat inappropriate things like elastic bands or plastic when they experience discomfort. Both cats and dogs tend to suck things when they have gastrointestinal issues: dogs often prefer to suck on their toys and cats prefer fleecy fabrics (vets call this strange feline phenomenon "wool sucking").

Neurological diseases

According to van Haaften, if any part of your pet's brain isn't functioning normally because of something like a tumour, a vascular event or inflammation, then you may witness extreme behavioural symptoms. They'll stand out because they're so abnormal, perhaps making you pause for a moment and think, "that was weird." You might brush them off or explain them away as new quirks among your pet's many odd behaviours, but they're worth paying attention to.

Watch out for changes in the way your pet interacts with its environment or with you. For instance, with dogs, look for odd repetitive behaviours such as fly snapping (compulsively biting at imaginary flies), tail chasing, flank sucking and aggressive behaviour that doesn't fit a normal pattern, isn't in response to any triggers or it doesn't serve any function (such a making a scary thing go away). Keep an eye out for physical symptoms like seizures or changes in the way your cat or dog walks, too.

Danielle Hodges is a Certified Professional Dog Trainer (CPDT-KA) and a Licensed Family Paws Parent Educator for dog, baby and toddler safety. She is co-owner of Follow the Leader Inc Dog Training School with locations in Toronto and Hamilton, Ont.