Seizures in Dogs

by Dr. Elizabeth Adkins DVM

Seizures are defined as abnormal electrical activity in the brain and can occur in dogs of any breed.  Seizures may range from very mild to severe and life-threatening.  Seizures may be referred to as fits or convulsions.  Often in seizures the patient will lose consciousness and collapse and the body will convulse.  During a seizure the dog may salivate, urinate or defecate.  Cluster seizures occur when the patient has multiple seizures within a 24-hour period.  Status epilepticus is the term for rapidly recurring seizures without complete recovery between seizures and is a life-threatening emergency.  During a seizure the owner should be very cautious about touching the dog to avoid being unintentionally bitten.  Seizures can occur in all species but are more common in dogs than other domestic animals.

Seizures consist of three components: the aura, the ictus and the postictal phase.  The aura is not always observed in dogs but during this phase the dog may hide, appear anxious or seek out their owners.  The ictus phase is when the dog loses consciousness and convulses.  During the postictal phase the dog may return to normal or may be restless, lethargic, disoriented and even blind.  The postictal phase can last for minutes to hours and the associated blindness often resolves but can last several days. 

Seizures can have a number of causes.  It can be helpful to categorize causes of seizures as intracranial (causes due to problems in the brain) or extracranial (causes due to problems not in the brain).  Common intracranial causes include epilepsy, genetic storage diseases, hydrocephalus, viral infections (e.g. canine distemper virus, rabies virus), bacterial infections, fungal infections (e.g. cryptococcosis), protozoal infections (e.g. toxoplasmosis, neosporosis), granulomatous meningoencephalitis, parasites, head trauma, neoplasia, thiamine deficiencies, toxicities (e.g. lead, organophosphates, strychnine, and tetanus) and blood clots.  Extracranial causes of seizures include low blood calcium levels (seen in lactating bitches and other diseases), low blood sugar levels, kidney failure, liver failure and liver shunts. 

Routine blood work can help to determine if the seizures are due to intracranial diseases or extracranial diseases.  These tests include a complete blood count, urinalysis, chemistry panel and titers for infectious diseases.  It is important to rule out extracranial causes of seizures as seizures secondary to extracranial diseases are unlikely to resolve unless the underlying disease is treated appropriately.  Once the extracranial causes of seizures are ruled out a computed tomography scan (CT) or magnetic resonance imaging scan (MRI), and cerebrospinal fluid (CSF) tap are indicated to determine any intracranial causes of seizures.

If the patient does not have any extracranial or intracranial abnormality causing the seizures then treatment for epilepsy may be started.  An effect from the treatment may not be seen until the patient has been medicated for at least 2 weeks.  In many cases multiple medications are required and these medications are usually required for life.  Treatment for epilepsy is not usually recommended in patients who have had only one seizure or have one seizure every few months.  Patients with recurrent and intense seizures should be treated with medications.  Some of the medications have a very wide dose range and negative side effects.  Repeated blood tests are needed to be certain that the blood levels of the drugs are high enough to control the seizures and to monitor for side effects.

The prognosis for dogs with seizures depends on a number of factors.  If the seizures are caused by extracranial diseases then the seizures are unlikely to resolve without treatment of the underlying condition.  If the seizures are due to an intracranial disease successful treatment may be difficult.  Intracranial diseases with poor prognoses include certain brain cancers, genetic storage diseases and canine distemper virus encephalitis.  The prognosis for dogs with epilepsy depends on the severity of the seizures and how well they are controlled with medications.  Dogs with cluster seizures typically have a poor prognosis.