Causes of Seizures in Dogs and Cats
Causes of seizures in dogs and cats may be broadly categorized as problems outside of the brain that secondarily affect the brain, primary structural problems within the brain, or idiopathic epilepsy.
Causes of seizures outside of the brain that secondarily affect the brain include abnormalities such as low blood sugar (hypoglycemia), poisons or toxins (such as Bufo toads), liver problems (such as a portosystemic shunt), electrolyte abnormalities (such as low blood calcium) and others.
Causes of seizures from within the brain (structural abnormalities of the brain) include brain tumors, strokes, encephalitis or meningitis, congenital abnormalities (such as hydrocephalus), head trauma, degenerative or storage diseases, infection and other causes.
The third broad category of causes of seizures in dogs and cats is idiopathic epilepsy. Idiopathic epilepsy is diagnosed when despite an exhaustive search for causes of seizures, no physical or metabolic problem can be found. Dogs with idiopathic epilepsy typically experience their first seizure between 1 and 5 years of age. There is often a regular pattern of seizure activity. Dogs with idiopathic epilepsy are typically normal between seizures and have a normal neurological examination, as determined by your veterinarian or a veterinary neurologist.
Idiopathic epilepsy is the most common cause of seizures in dogs. It is very uncommon in cats.
There are several other diseases in dogs and cats that can mimic seizures. These include:
1. Syncope: a heart or lung problem that may cause fainting or seizure-like activity.
2. Vestibular Disease: a balance problem that may cause dogs to roll on the ground that may be confused with a seizure.
3. Neck Pain can sometimes be mistaken for a seizure.
4. Pruritus, or extreme itchiness has been mistaken for a seizure.
5. Movement disorders–such as idiopathic head bobbing in English Bulldogs.
6. Neuromuscular disease can sometimes lead to collapse, which may be mistaken for a seizure.
It is very important that the episode is accurately categorized as a seizure to avoid the wrong diagnostic pathway (e.g. performing unnecessary tests). A complete description of the episode is useful to the veterinary neurologist, including when the episodes happen; how long they last; what the patient is doing before, during and after the episode; how frequent they happen; whether the patient loses control of urination or defecation; if the episode starts at one part of the body or face; and does the patient lose consciousness. These are just some of the questions that may be asked. Providing a video of the episode is often useful.
Seizures in Dogs and Cats–Diagnosis and Treatment
Seizures in dogs and cats may be caused by a variety of conditions, including problems inside the brain, problems outside of the brain and idiopathic epilepsy.
Accurately diagnosing the underlying cause of the seizure is important as it affects how the veterinarian treats the seizure and the likelihood of controlling the seizure.
The first and most important step is a thorough examination by a veterinarian. Common ‘mimickers’ of seizures can be identified. A thorough neurological examination can also help the veterinarian determine whether the cause is more likely to be within the brain or not.
Most of the causes of seizures outside of the brain can be diagnosed or ruled out with blood and urine tests and potentially X-rays. X-rays of the head are NOT sensitive enough to see inside the brain. Therefore, other tests are necessary to diagnose or rule out causes inside of the brain. The tests that are often used by veterinary neurologists to look inside the brain include an MRI and CSF analysis. CT scans or low-field MRI may give some information about the brain, but are much less sensitive than high-field MRI.
At Southeast Veterinary Neurology, we take a step-wise approach to seizures.
First, a detailed account of the pet’s seizure episodes is taken. This helps us determine the seizure frequency, severity, and duration; the age at which seizures started; medications that have been tried and response to those medications; how the pet acts before and after the seizures; and many other important factors.
Second, a thorough physical examination and neurological examination is performed. This identifies potential other causes of episodes (e.g. sometimes severe heart problems can mimic seizures). It also helps identify other co-existing abnormalities that may be important in determining the cause and/or treating the seizures. Finally, it guides the neurologist’s list of potential causes. For example, dogs with idiopathic epilepsy typically have a normal neurological examination between seizures. An abnormal neurological examination suggests that idiopathic epilepsy is less likely.
Next, baseline tests are performed. These tests may include blood tests (complete blood count, serum chemistry panel), urinalysis, thyroid testing, and potentially X-rays of the chest and abdomen. These are necessary to diagnose or rule-out causes outside of the brain (metabolic or extracranial causes), to identify co-existing conditions and to prepare for anesthesia, which is necessary for the next level of testing.
If the cause has not been identified, if there is an abnormal neurological examination, if the patient is of an atypical age for idiopathic epilepsy (i.e. less than 1 year or older than 5 years), or if they are of a breed that is predisposed to certain intracranial problems (e.g. encephalitis or brain tumors), then advanced testing is indicated. An MRI is the best way of visualizing the brain and identifying structural problems such as brain tumors, strokes, encephalitis or congenital malformations. A CSF analysis (‘spinal tap’) is sometimes performed to provide additional information such as identifying meningitis, infections or certain types of tumors.
Based on the results of this step-wise approach, an accurate diagnosis can be achieved and appropriate treatment may be prescribed.
Treatment of Seizures
Treatment of Seizures in Dogs and Cats depends on the underlying cause. For example, a dog with low blood sugar is treated very differently than a dog with a brain tumor. A dog with a stroke is treated differently than a dog with encephalitis.
In addition to treating the underlying cause, medications are used to decrease the frequency, severity and duration of seizures. The following are medications that are often used by veterinarians to treat seizures in dogs and cats.
1. Phenobarbital–this is a common first-line medication to treat seizures in dogs and cats. It is administered twice daily. Side effects include sedation, incoordination, increased thirst and urination and increased appetite. These typically improve after a few weeks. Phenobarbital is metabolized by the liver and can cause elevated liver enzymes on blood testing. It rarely can cause liver damage and/or bone marrow suppression. Blood tests to monitor for side effects and to measure drug levels in the body are performed regularly (every 4-6 months).
2. Potassium Bromide–this is also a common first or second-line medication to treat seizures in dogs. It can cause lung problems in cats and is therefore not used frequently in cats. It is not metabolized by the liver, so it is useful in dogs with liver disease. Side effects may include sedation, incoordination and increased thirst and urination. Potassium bromide has sometimes been associated with pancreatitis, stomach upset and/or a stiff gait. Blood tests are also performed regularly to monitor for adverse effects and to measure drug levels in the blood.
3. Levetiracetam (Keppra)–this is a common first or second-line medication. It is typically administered three times daily, however, an extended-release formula is now available that is given twice daily. Adverse effects appear to be minimal.
4. Zonisamide–this is a sulfa-class medication that is used as a second or third-line treatment, however, it can also be used as a first-line therapy. Side effects may include decreases in tear production or ‘dry eye’, but also may have some immune-mediated reactions. It is given twice a day.
5. Felbamate–has less potential for side-effects (less sedation). However, it is relatively expensive, especially for large dogs. It requires three-times per day dosing.
6. Gabapentin–Fourth-line medication at Southeast Veterinary Neurology.
7. Diazepam–is useful to stop seizures in an emergency. It can be given intravenously or rectally. Oral valium is typically not useful as a ‘maintenance’ medication.