EPILEPTIC SEIZURES IN DOGS
Author: Carlos Ros Alemany
Ldo. Vet, MRCVS, Dipl. ECVN, EBVS® European Diploma Specialist in Neurology
Veterinary, Acrd. AVEPA Neurology, Neurology/Neurosurgery Service Memvet-
Veterinary Reference Center Palma de Mallorca
In this article, Carlos Ros Alemany, with a European Diploma in Veterinary Neurology, comments on the most important aspects of epileptic seizures in dogs.
Epilepsy is the most common chronic neurological problem in dogs, with an estimated prevalence of 0.6-0.75% in the general dog population. Approximately half of dogs with epilepsy are diagnosed with idiopathic epilepsy,although there are several ways and means of classifying epileptic seizures, mainly based on etiology and according to type.Epileptic seizure
, are those originating in the prosencephalon (thalamus-cortex) and are defined as "hypersynchronous neuronal electrical activity in the cerebral cortex, manifesting as a transient and paroxysmal abnormality of consciousness, motor activity, autonomic, sensory and cognitive function". There are multiple causes (genetic, traumatic, hypoxic, tumors, infection/inflammation, metabolic problems...) which provoke an increase in neuronal excitability and an excessive and prolonged depolarization of neuronal groups.
Etiological classification of epileptic seizures in dogs
a) Structural epilepsy, those epileptic seizures that occur as a consequence of physical, structural and symptomatic intracranial lesions affecting the forebrain.Such diseases include: cerebrovascular accidents, inflammatory/infectious diseases, neoplasms, neurodegenerative diseases, among others.
b) Idiopathic epilepsy, which is characterized by the appearance of 2 or more spontaneous epileptic seizures, separated by 24 hours, with no identified etiological agent and with suspected genetic predisposition. It is classified as:
- Genetic epilepsy: there are few breeds in which genetic testing can be performed for the detection of epilepsy (so in general it is a disease of diagnosis by exclusion).
- Suspicion of genetic epilepsy (breeds with racial predisposition, or family history of epilepsy...).
- Epilepsy of unknown cause when the cause is not structural and the cause is not determined.
c) Epilepsy of unknown cause (previously known as cryptogenic epilepsy)i.e. patients with epileptic seizures, in which diagnostic tests are performed, with normal results, and are not typical of idiopathic epilepsy.
d) Reactive seizures:those that occur as a consequence of intoxications, metabolic/endocrine or nutritional alterations.
Classification by type of epileptic seizures
a) Focal seizures: regional or lateralized signs / involvement of part of the brain tissue. Types: motor (facial tremors, blinking, head jerking, repetitive limb movements), autonomic (dilated pupils, hypersalivation or vomiting) or behavioral-sensory (anxiety, sudden fear and restlessness). The mental status may be normal or altered.
b) Generalized seizures: involvement of both cerebral hemispheres. They can be tonic, clonic, tonic-clonic or atonic. In these, there is a loss of consciousness and there are associated autonomic signs.
c) Focal seizures that evolve to generalized: in these, the patient starts with focal signs (involvement of a region of brain tissue) and evolve to generalized (involvement of both cerebral hemispheres).
d) Reflex seizures: precipitated by external or internal stimuli. Typical: myoclonic epilepsy.Sometimes, they have a genetic origin (Lafora disease: neurodegenerative disease described in Beagles, Miniature Shorthair Teckels and Bassets Hounds).
Phases of epileptic seizures
- Prodrome: just before the seizure. It can be predicted (↑anxiety, restlessness, hiding).
- Aura: initial manifestation of the seizure (stereotypies, autonomic signs, barking...); this term is no longer used in veterinary medicine as the sensations before a seizure are subjective and this in animals cannot be assessed.
- Ictus: "seizure phase", involuntary movements/behaviors. During this phase (if any) the patient will show autonomic signs.
- Post-stroke: after the seizure. It can last from seconds to days. Sometimes it is the only thing the owner observes. The patient may show abnormal behavior, disorientation, appetite, vomiting, blindness, compulsive walking or even episodes of aggression.
Frequency of epileptic seizures
- Occasional episodes.
- "Clusters" of seizures: presence of 2 or more seizures in a 24-hour period and between them, the neurological examination is normal.
- "Status epilepticus": seizure of more than 5 minutes duration, or two or more seizures in a row without complete recovery of neurological normality between them within 24 hours.
Clusters" of seizures and "status epilepticus" are neurological emergencies.