Possible medical causes for aggressive or unusual behavior in dogs

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 There are many conditions that can cause unusual or aggressive behavior in dogs

It is advisable that at the onset of any sign of aggression, all possible medical causes are ruled out BEFORE you consult a trainer.  If an injury, disease, or genetic congenital defect is deemed the cause of the dog’s mood swings or aggression, then no training will be effective until the problem has been resolved or controlled.

There are many conditions that can cause unusual or aggressive behavior in dogs:  anything from problems with teeth and eyesight to joint pain.  If the temperament problem is genetic in nature then the likelihood that the animal can be completely cured of the aggression is minimal. The treatment would then concentrate on the “management” of the behavior rather than an absolute cure.

Other conditions (like Hypothyroidism) can be effectively treated with medication prescribed by your veterinarian. Any condition which causes inflammation of the brain can also cause neurological problems, including aggression. A chemical imbalance can make their behavior unstable and medication may be required to rectify the problem. A dog in pain can react in a defensive or aggressive manner.  Consult your veterinarian for a diagnose.


Some of the conditions that have been linked to aggression in dogs are:


This condition is not unlike clinical depression, obsessive compulsive disorders, etc., in humans. Serotonin plays an important role in the neurochemical control of aggression in the brain, especially when a component of impulsivity is present. As with humans, the family of SSRI drugs have the most success in combination with “therapy” i.e., behavior modification techniques. There are not many behavior cases which will respond to medication alone.  Cognitive Dysfunction Syndrome which is associated with age related degeneration can be managed through medication and environmental and behavioral modification.


A common endocrine disease where the body produces an abnormally low amount of thyroid hormones. An autoimmune destruction of the thyroid gland, which affects more than 50 dog breeds and crosses.


Distemper and rabies are a viral form of Encephalitis.  There are two common forms of Encephalitis: acute encephalitis commonly seen in young dogs or puppies and chronic encephalitis seen in older dogs, even those with a good vaccination history.


This is a medical term meaning low blood sugar. Symptoms of a hypoglycemic attack can include: staggering or collapse, weakness, aggression, moodiness, glassy eyes, staring, dazed look.


Also referred to as “water on the brain”.  It is a condition that affects the toy breeds and the brachycephalic dogs with very short noses, like the boxer, pug, etc.


There are many causes of epilepsy so diagnosis is not always easy.  Primary epilepsy is a hereditary condition which is more common in certain breeds.  Other causes include canine distemper, encephalitis, meningitis, poisonings, liver and kidney disease, head injuries, brain tumors, strokes and cerebro-vascular disease, hydrocephalus, etc.  Many of the causes of epilepsy still remain obscure.


A brain tumor can cause changes in temperament.  Some or all of these changes might be observed in an animal afflicted at varying times and degrees:  changes in mental status, aggression, confusion, irritability, increased vocalization, apathy, hyper excitability, tremors, weakness, disorientation, visual deficits, circling, falling, irregular sleep habits, abnormal postures, exaggerated gait, head tilt, pain, house soiling, staring, trembling, decreased appetite, seizures, paralysis.


When the brain has suffered trauma or injury, swelling or bleeding may result. This swelling or bleeding will interfere with the normal function of that part of the brain. Many unusual neurological symptoms can result, including aggression.


Also referred to as “rage syndrome”. Partial seizures occurring in a region of the brain that controls aggression can cause sudden unprovoked aggression.

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 Medical Causes of Aggression In Dogs by: Dr. Nicholas Dodman http://www.petplace.com/articles/artShow.asp?artID=1807

My Pet has Changed: Understanding Aging-Related behavior Changes in Dogs“, summary of presentation by Dr. Ilana Reisner, at the Annual Cannine Symposium held at VHUP

Impulsivity in Dogs – Assessment and Treatment
by Jaume Fatju, Spain, World Animal Veterinary Association, World Congress – Vancouver 2001, (discusses brain chemistry in terms of impusivity and aggression)

Behavior-Medicating Misbehavior in Dogs
First printed in the October, 1997, issue of Your Dog newsletter from Tufts University School of Veterinary Medicine, Columbia Animal Hospital, Columbia, MD

Epilepsy in the Dog
The UK National G.S.D. Help Line

Rule Out Hypoglycemia
by Darleen Rudnick, Pet Nutritionist

Thyroid Dysfunction as a Cause of Aggression in Dogs and Cats
L.P. Aronson DVM & N.H. Dodman RVMS
Presented at the 43. Jahrestagung der Deutschen Veterinarmedizinischen
Gesellschaft Fachgruppe Kleintierkrankheiten
29-31 August 1997 in HCC Hannover

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Welcome to Spike’s Dog Blog by Acme Canine. Throughout the site, you will find a variety of helpful dog training articles, insightful dog behavior tips, and truthful product reviews from nationally-recognized canine trainers and professionals.