Seizures

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Overview

Seizures are common in dogs and also occur occasionally in cats as well. A seizure is a neurological episode that is sudden in onset, repeatable in nature and that usually involves some disturbance in consciousness along with uncontrolled movements and unintended visceral functions such as urination. Seizures have a wide variety of causes, which can include birth defects such as hydrocephalus, metabolic defects like liver dysfunction, brain tumors, brain infections such as encephalitis, or a brain abscess, toxins such as lead and vascular disorders such as strokes and high blood pressure. Perhaps the best-known cause of seizures in dogs is idiopathic epilepsy, which is probably caused by either a genetic mutation, a microscopic brain malformation or possibly a birth injury. Epilepsy in dogs usually causes seizures to start between one and five years of age. If a dog starts to have seizures before one year of age then the cause is usually not epilepsy but rather some other disorder such as liver dysfunction. If an animal starts to have seizures after 5 years of age then it is also less likely to be due to epilepsy. After 7 years of age there is a much greater chance that the seizures are caused by another disorder such as a tumor or vascular disease. Some conditions like encephalitis can occur at any age.

Treatment of seizure disorders is dependent on first making an accurate diagnosis. For example, treatment of a liver disorder such as portosystemic shunt, or an encephalitis due to a tick-borne disease, is unlikely to be successful using phenobarbitone and will require more specific management. Diagnosis of the specific cause of a seizure disorder depends on taking a good history and then performing a good physical and neurological examination. This is followed by blood tests, which should always include assessment of liver function using a bile acids test. If these are normal then the next step is to image the brain using a CT scan or an MRI. These imaging techniques should detect structural diseases that alter the normal anatomy of the brain, such as a tumor or a stroke. If imaging is normal or if the diagnosis is still unclear then imaging is followed by a spinal tap in order to obtain cerebrospinal fluid (CSF) for microscopic analysis. CSF analysis should detect inflammatory diseases that may have no effect on anatomy but that cause an influx of white blood cells into the brain.

Figure 8: MRIs from a dog with idiopathic epilepsy to show the amazing resolution obtained. The tongue (*) can be seen clearly in the dog’s mouth and its brain (arrowheads) is shown in exquisite detail. A: This image shows the spinal fluid that surrounds and circulates through the brain as dark in color. B: This image show the spinal fluid as white and it also display the different types of brain tissue more clearly. This difference is seen most clearly in the cerebellum, shown by the arrow.

The main anticonvulsant drugs used to treat seizures in dogs are phenobarbitone and potassium bromide. Diazepam (Valium) may be used intravenously or administered into the rectum in order to stop a dog from having multiple seizures (often called a cluster of seizures). Diazepam is not useful for long-term control as it persists in the body for less than an hour. If phenobarbitone and potassium bromide are not successful in controlling the seizures then other, more expensive anticonvulsants may be employed such as Keppra, felbamate and zonisamide.

Seizures in cats may be due to epilepsy but are more commonly caused by other disorders such as encephalitis or vascular disease. Seizures are diagnosed and treated in the same way as they are in dogs although potassium bromide can cause feline asthma and so is not usually recommended unless other therapies have been unsuccessful.

The prognosis is good for most dogs and cats with epilepsy. About 80% of animals with epilepsy can be controlled using anticonvulsants although it is unusual for the seizures to stop completely. In most the seizures usually decrease in frequency and severity so that they are much more manageable but most animals will require lifelong treatment. The prognosis for animals that have seizures caused by conditions other than epilepsy will depend on the condition itself. The most common complications with epilepsy are either poor overall seizure control or sporadic clusters of seizures that occur in otherwise well-controlled animals.

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