Epileptic seizures in dogs: clinical signs and causes
Some breeds are more likely to suffer epileptic seizures, such as the German Shepherd, Beagle, Golden Retriever and Labrador Retriever. The life expectancy of affected dogs depends on several factors. One study found that idiopathic epilepsy has a worse prognosis and that intact dogs usually live longer.
What is epilepsy?
A seizure is produced by abnormal electrical activity in the brain as a result of the spontaneous depolarisation of neurons, which, in turn, may be due to excessive excitation or loss of inhibition. These disruptions in the brain cause sudden, transient changes in the dog’s behaviour and/or movement.
Epileptic seizures in dogs usually occur in the middle of the night. This is because, among other factors, certain groups of neurons that are only slightly hyperactive during waking hours become more excitable when the dog is asleep.
The clinical signs of epileptic seizures change as the dog goes through different phases:
- Prodromal. This phase, observed in 10% of epileptic dogs, precedes the convulsions and may last just a few minutes or continue for several days. It tends to manifests as a state of restlessness.
- Aura or pre-ictal.This phase may last just a few seconds or a few minutes, then the epileptic seizure begins as it is a focal seizure that generalises rapidly. It can produce behavioural, motor, sensory and/or autonomic dysfunction.
- Post-ictal. This phase may last for hours or days after the seizure. Most dogs suffer behavioural changes as a result of cerebral exhaustion, they tend to be ataxic, tired and sometimes aggressive.
Epileptic seizures in dogs: The clinical signs are determined by which area is affected
Most epileptic seizures in dogs occur suddenly, last a few seconds or minutes, and stop by themselves. The clinical signs vary depending on which area of the brain is affected.
- Focal seizures. These only affect half of the brain and are confined to a specific region, so the clinical signs depend on the area affected and its functions. In some cases, dogs produce episodic movements such as facial contractions, rhythmic blinking, shaking of the head or muscle contractions in a limb. In other cases, we can observe autonomous signs such as excessive salivation, vomiting and dilated pupils. There may also be behavioural changes including restlessness, anxiety or inexplicable fear.
- Generalised seizures. These occur in both cerebral hemispheres, so dogs typically lose consciousness and show autonomous signs such as salivation, urination and defecation. Movements usually affect both sides of the body. They may be tonic, which involves muscle rigidity, clonic, involving fast and rhythmic involuntary muscle contractions, tonic–clonic or myoclonic movements, which manifest as sporadic jerks. Some dogs may suffer atonic seizures, resulting in a sudden and general loss of muscle tone, with the dog collapsing.
- Focal seizures that evolve into generalised seizures. This is the most common type of epileptic seizure in dogs; it starts with a focal seizure that develops into a generalised seizure. The focal seizure is normally very brief and hard to detect, as the secondary generalisation follows almost immediately.
Causes of epileptic seizures in dogs
Each dog is different, so vets and owners must look for the causes of epileptic seizures on an individual basis. According to one study, idiopathic epilepsy tends to affect dogs aged between 6 months and 6 years and represents approximately 48% of cases. When the presence of a hereditary pattern can be confirmed, it is called primary epilepsy. Even so, in some cases it may be due to extra- or intracranial causes:
- Extracranial causes. About one third of these instances are due to metaldehyde or insecticide poisoning. Another third is due to hypoglycaemia or insulin overdose. Around 10% are a consequence of hepatic encephalopathy due to a portosystemic shunt and 5% are caused by hypocalcaemia.
- Intracranial causes. These may be inflammatory, vascular, neoplastic or degenerative in nature. Head injuries also increase the risk of developing epilepsy, as reported in this study. However, it is estimated that 4 out of 5 cases of epileptic seizures in dogs of an intracranial origin are either neoplastic or inflammatory in nature. Although less common, epilepsy can also stem from a stroke, distemper or granulomatous meningoencephalitis.
Occasionally, an MRI scan and/or cerebrospinal fluid analysis can reveal a structural anomaly, which is classified as structural epilepsy, but the damage cannot always be detected.
