If your otherwise good-natured dog suddenly displays aggressive behavior -- whether toward you, another person or another pet -- you must get to the bottom of it. You also must examine your dog's previous behavior. Sometimes, that "sudden" aggression actually occurs after your dog has given you various warning signs that you didn't heed.
While some dogs react aggressively without apparent sign or provocation, it's possible that the threatening behavior was being communicated. Early signs of aggression that can ramp up in severity include mouthing to control an individual or animal, or a dog punching a person with his nose. The dog might exhibit changes in posture, vocal patterns and facial expression prior to the attack. Think about any potential triggers. Was food or canine territory involved? Did your dog appear scared before biting? Did the attack happen during a thunderstorm or after another loud noise? Did anyone touch the dog, even gently, beforehand? These clues can help you, your vet and a canine behaviorist figure out the aggression's cause.
Sudden aggression could result from pain and certain medical conditions. That's especially true in older dogs who have otherwise displayed a good temperament all of their lives. Hypothyroidism, or insufficient levels of thyroid hormone, often affect older dogs. Physical symptoms often include hair loss, skin infections and increased drinking and urination, but irritability and subsequent aggression are also factors. Other medical issues responsible for sudden aggression include epilepsy, brain tumors and head trauma. Certain medications, such as tramadol for pain, can cause aggressive reactions in some dogs. Your vet can conduct blood and biochemical tests, along with X-rays and ultrasounds, to get to the root of your dog's problem. Some diseases, including hypothyroidism and epilepsy, can be controlled with medication and your pet's former personality should return.
Rage syndrome, also known as sudden onset aggression, occurs when an otherwise docile dog attacks someone out of the blue. There's no obvious trigger. During the incident, the dog appears disoriented and might remain so after the attack, then gradually becomes his normal self. While rare, rage syndrome appears more often in certain breeds, including the cocker spaniel, English springer spaniel, golden retriever, German shepherd, Doberman pinscher, bull terrier, Saint Bernard, Chesapeake Bay retriever and Bernese mountain dog. If you believe your dog suffers from rage syndrome, take him to the vet for a thorough examination. While it's possible that antidepressants or anti-seizure medications can stop the onset of attacks, your vet may suggest considering euthanasia if the dog does not respond to drug or behavioral therapy and all other options have been exhausted.
If your vet can't find a medical reason for your dog's behavior, ask her to recommend a certified veterinary or canine behaviorist. Your vet might prescribe medication to help treat aggression, but drugs alone won't work. If your dog is intact, spaying or neutering can ease the situation. The behaviorist can work with you and your dog to create an individual treatment plan for your situation.