Seizures in dogs can be caused by many different illnesses. As a result, if your dog has a seizure, your veterinarian will need to perform some diagnostic tests before a proper course of treatment can be determined.
Seizures vs. Epilepsy
If your dog has more than one isolated seizure, your veterinarian may call the illness epilepsy. Primary, or idiopathic epilepsy is epilepsy that is not caused by any underlying brain lesion or other illness. Acquired epilepsy is epilepsy that due to an underlying abnormality such as a brain tumor. Regardless of the terminology, the process of diagnosing epilepsy involves the same testing procedures as those used to diagnose seizures.
Obtaining a History
One of the very first things your veterinarian will do is to perform a thorough physical examination for your dog, looking for obvious abnormalities. Neurologic and muscle reflexes such as muscle stiffness or tremors can lend helpful clues.
Your dog's history also needs to be taken into account. Some diseases tend to occur in a certain age group or even in a specific breed of dog. Knowing your pet's age, breed, and physical history can help your veterinarian determine which diseases are most likely to be causing your dog's seizures and help determine which lab tests are most important to perform.
Initial Basic Testing
Your veterinarian will perform three initial tests on your dog:
- A complete blood cell count looks at both the red blood cells and the white blood cells in the blood. This test can indicate whether your dog is anemic. It can also help determine, in conjunction with other tests, whether or not your dog is dehydrated. Changes in white blood cell counts can indicate infection or other pathological diseases that affect the bone marrow, such as certain forms of cancer.
- A blood chemistry profile includes tests for kidney function such as the blood urea nitrogen (BUN) and creatinine. It also looks at your dog liver enzymes and bilirubin levels, which can help determine the state of the liver. Protein levels in the blood are measured. Blood glucose levels will be checked and electrolytes such as calcium, potassium, sodium, and phosphorus are also measured.
- A urinalysis, an analysis of the urine, helps determine whether your dog's kidneys are able to concentrate the urine and conserve the body's water effectively. This test also looks for evidence of abnormal substances in the urine, such as blood, protein, bilirubin, crystals, and others.
Radiographs, more commonly know as x-rays may be recommended. While x-rays cannot see inside the brain, it can sometimes give other important information, especially if your veterinarian is concerned about cancer. Most types of cancer, if they spread (metastasis), will spread to the lungs. An x-ray of the chest may be recommended to look for metastatic cancer before recommending your pet undergo more invasive or expensive testing.
Additional Blood Testing
In some cases, further blood testing may be warranted as well.
If your veterinarian suspects a liver disease in your dog, a bile acid test may be recommended. Often, the bile acids are measured before your dog is fed and then again shortly after eating a meal. This can help detect diseases that affect both the liver and brain, such as a portosystemic shunt ("liver shunt").
Thyroid testing may be required, especially in dogs where hypothyroidism can contribute to seizure activity.
Testing for specific infectious diseases may also be recommended to rule these out as causes of the seizures. This may include testing for diseases such as toxoplasmosis, canine distemper virus, and others. Your veterinarian will help decide which diseases are most likely and which need to be investigated as a cause of your dog's seizures.
Cerebrospinal Fluid (CSF) Analysis
If the initial blood and urine testing do not indicate the cause of the seizures in your dog, your veterinarian may recommend a cerebrospinal tap. This allows the collection of fluid that surrounds and protects the brain and spinal cord. This test may help establish a diagnosis such as meningitis (inflammation of the membrane that surrounds the brain and spinal cord) or encephalitis (inflammation of the brain) as well as other conditions that may contribute to causing seizures and/or epilepsy.
Diagnostic Imaging of the Brain
Tests such as magnetic resonance imaging (MRI) or computerized axial tomography (CAT or CT scan) are specialized tests that can examine the structure of the brain itself, looking for anatomical abnormalities, lesions, or areas of inflammation. These tests may be recommended for some dogs suffering from seizures and/or epilepsy, but the availability of these tests is often limited to specialized facilities.
An electroencephalogram, or EEG, can measure the electrical activity of your dog's brain. It is sometimes used to aid in localizing the point in the brain where a seizure originates, but standardized norms for EEG in the dog have not been established.
Berendt M, Löscher, W., Muñana, K. et. al, ACVIM Fact Sheet: Idiopathic Epilepsy. American College of Veterinary Internal Medicine, 22 February, 2016. doi:https://doi.org/10.1111/jvim.13841
Canine Idiopathic Epilepsy. University of Missouri College of Veterinary Medicine, 2020
De Risio, Luisa et al. International Veterinary Epilepsy Task Force Consensus Proposal: Diagnostic Approach To Epilepsy In Dogs. BMC Veterinary Research, vol 11, no. 1, 2015. Springer Science And Business Media LLC, doi:10.1186/s12917-015-0462-1