What is a shiver? What is a seizure?
Shivering is a way to help your dog raise their body temperature and warm up. Dogs may shiver when they’re cold, as well as when they’re nervous or fearful. Some medical issues can also cause your dog to shiver, or tremble, such as tremorgenic mycotoxins (usually from ingestion of garbage or compost) or certain electrolyte imbalances, which could make muscle twitches easier to elicit. A seizure, on the other hand, is a symptom of a problem affecting the forebrain. A seizure could be caused by a range of potential triggers that are inside or outside the brain. Those triggers could include:
Dogs are also prone to “meningoencephalitis of unknown origin” (MUO) which can cause seizures, Dr. Lau says. This is an umbrella term encompassing groups of non-infectious and non-contagious inflammatory disorders of the brain that are believed to arise from an overactive immune system. Toy dog breeds, such as Maltese and Yorkshire Terriers, and other breeds such as French bulldogs and Pugs, have a higher incidence of meningoencephalitis of unknown origin. Researchers have still not discovered the exact cause of the condition (hence the “unknown origin” part of the name) and the causes may be a combination of both genetics and environmental factors. Dr. Lau notes that most dogs who suffer from these inflammatory conditions tend to respond well to immune suppressant medications and anti-seizure medications as a long-term treatment.
Why is this important, shaking is shaking? I hear you ask.
Shaking is never just shaking. It is rather a broad term that can easily over-simplify a far more complex range of conditions. The first distinction we should try and make is whether it is tremors or seizures. This is important as the possible causes, diagnosis and treatment differs between the two.
What is the difference between tremors and seizures?
Unfortunately, it is sometimes difficult to differentiate tremors from seizures as both involve abnormal muscle contractions.
Tremors are involuntary muscle movements occurring while the dog is awake. During episodes the dog remains aware of its surroundings and does not lose consciousness.
Seizures on the other hand are subcategorised into 2 types:
Typically dogs with generalised seizures will fall onto their side, will become stiff and paddle all four limbs. They usually become unconscious and may pass urine/faeces, salivate excessively or vomit. These are known as generalised or grand mal seizures.
Some dogs exhibit partial/focal seizures, meaning that rather than the whole body being affected, only a single limb or possibly only the face may be affected by abnormal movement (e.g. lip smacking, fly catching). They may or may not lose consciousness, meaning that it may be difficult to differentiate these seizures from tremors.
Some dogs may show behaviour changes prior to a seizure, for example becoming quieter, anxious, hiding, pass urine/faeces etc. We call these pre-ictal signs. Typically, dogs will exhibit behaviours after a seizure such as unsteadiness on their feet, quieter demeanour etc that may last from minutes to hours. We call these post-ictal signs.
There are numerous possible causes of tremors. These include:
For some small breed dogs (for example Chihuahuas and Yorkshire Terriers), episodes of shaking can be normal. For many there is no obvious underlying cause or evidence of associated illness and no need for treatment. (However, if it starts suddenly, it’s always best to rule out more serious issues before assuming that this is the cause – Ed.)
Some dogs show significant shaking associated with excitement or due to stress and anxiety.
Dogs will shake if they are cold or wet for extended periods of time.
Shaking may be an indication that dogs are painful. Importantly, not all dogs who are uncomfortable will shake.
Muscle weakness in the hind limbs is not uncommon in dogs, especially as they get older. This can result in trembling of the hind limbs, particularly as they get up from rest.
Blood changes including low blood sugar, low blood calcium (sometimes observed in pregnant dogs) or electrolyte abnormalities can cause trembling/shaking.
This condition typically affects small breed white dogs (e.g. Maltese and West Highland White Terrier). Affected dogs show repetitive involuntary muscle contractions that affect the entire body or are localised to a particular area (for example a limb or the head) from approximately 1-2 years of age. It typically occurs with exercise but dogs are normal between episodes. This syndrome responds well to treatment with steroids, with a significant improvement usually noted within 1-2 weeks.
Intermittent episodes of abnormal movements occurring as attacks with no loss of consciousness. Different movements are noted, but most commonly these involve the hind limbs and can be sufficient to prevent the dog from walking. Attacks can last anywhere from a few minutes to hours and may be triggered by excitement or exercise. It is often difficult to differentiate these from partial seizures.
There are a number of different causes of seizures in dogs. These include:
This is the most common type of seizures seen in dogs and will typically start between 6 months and 6 years of age. After diagnostic testing such as bloods and MRI scanning of the brain, no underlying cause is found. They can occur in any breed but are more frequently observed in certain breeds e.g. Border Collies. Epileptic seizures can occur with varying frequency and for some animals their control with anti-seizure medications is required.
Any head injury can result in seizures.
Ingestion of certain toxins can cause sudden onset seizures in previously healthy dogs. These include but are not limited to slug bait, chocolate and xylitol (sugar alternative in chewing gum).
Things such as low blood sugar (for example in diabetic dogs given excessive insulin, or puppies who have not eaten for a while) can result in seizures occurring. Dogs with liver function problems can fail to effectively filter toxins from the blood stream which can result in seizures. This can be due to developmental issues (e.g. portosystemic shunts) in younger dogs, or severe liver disease in older dogs.
Brain tumours are an uncommon cause of seizures, but are more commonly seen in older dogs.
Certain infections/inflammatory conditions (e.g. meningitis) affecting the central nervous system and the brain can cause seizures.