If your dog suddenly becomes aggressive toward you or to someone else, you need to start with some soul-searching. Is this really the first indication that you’ve had from your dog that he may have aggressive tendencies? True sudden or acute aggression is actually pretty rare in most dogs, and as veterinarians, we find that once we discuss the problem thoroughly with the pet parent, there have been warning signs in the past.
If your dog truly has never shown aggressive tendencies, and does so suddenly, read on to learn some possible causes that should be investigated.
Primary brain disease
Some diseases affect brain tissue. If the disease reaches the area of the brain that controls behavior, it’s possible that a dog could exhibit very sudden changes in its behavior, including aggressive tendencies. Strokes, tumors and infections of the brain can all affect this area.
For this reason, it’s critical that your dog be evaluated by your veterinarian for any episodes of sudden aggression. A thorough physical examination that includes careful evaluation of all of the cranial nerves (the nerves that originate within the skull cavity) will provide clues that will help to establish whether brain disease is a possibility.
Hypothyroidism is one of the most common hormonal diseases we see in dogs. It typically occurs around middle age, and it’s suspected to be an autoimmune disease in which, for reasons we can’t explain, the body destroys its own thyroid tissue. This leads to a significant drop in the amount of hormones that are produced by the thyroid gland and subsequently a decrease in the rate of metabolism. It’s thought that hypothyroid dogs may develop aggressive tendencies that resolve once the disease is treated; however, more research is needed to establish a definitive correlation.
Cushing’s disease is another hormonal disease that occurs in dogs and involves an increase in the amount of cortisol that is produced in the body. Cortisol is frequently referred to as the body’s “stress hormone,” and dogs with Cushing’s disease can exhibit behavioral changes, including aggression.
In both of these cases, lab tests can help your veterinarian understand whether a dog that has exhibited sudden aggression may be affected, so again, be sure you have your dog examined for aggressive episodes.
Drugs that impact the way that the neurotransmitter serotonin is metabolized in the body are sometimes used to treat anxiety in dogs. These drugs are called “serotonin reuptake inhibitors” and examples include Prozac and Zoloft. These drugs are widely used in human medicine, and although their use in veterinary patients is relatively recent, they can very positively impact many dogs with severe anxiety issues.
The problem is that certain other medications can “ramp up” the effects of these drugs and produce a syndrome that is widely recognized in people called “serotonin syndrome.” The result is often hyper-excitability in people. It’s thought that dogs can also experience serotonin syndrome, and suddenly aggressive behavior could be the result.
An overdose of SSRIs can also cause serotonin syndrome, so if someone in your household takes these medications, ensure that they are always stored well out of your dog’s reach.
Even a normally docile dog may be prompted to lash out in an aggressive manner if he experiences sudden pain. A friendly pat to a painful region along the spine can especially trigger this, so make sure that your veterinarian carefully evaluates your dog’s entire body for painful areas if he suddenly becomes aggressive.
Canine cognitive dysfunction
Canine cognitive dysfunction is a well-recognized problem in older dogs. We believe that it may be due to a process similar to the destruction of the brain tissue that occurs in human Alzheimer’s patients. CCD can cause the development of aggressive tendencies in older dogs, and other symptoms include insomnia, apparent confusion (i.e., ending up in unusual places in the house or standing and staring at an object without moving) and loss of learned behaviors such as house-training.
There are treatments for CCD, and although not all dogs respond, many can improve with the use of specific supplements, diet change and medications to improve sleep quality and anxiety.
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