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, our veterinarian with a European Diploma Specialist in Veterinary Neurology, tells us the most important things about 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. About half of dogs with epilepsy are diagnosed with idiopathic epilepsy, although there are several ways and means of classifying epileptic seizures, mainly based on their etiology and depending on the type. The Cconvulsions
epileptic are those that have their origin in the forebrain (thalamus-cortex) and are defined as a "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 cause 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 occur as a consequence of physical, structural, and symptomatic intracranial lesions affecting the forebrain. These diseases include: cerebrovascular accidents, inflammatory/infectious diseases, neoplasms, neurodegenerative diseases, among others.
b) idiopathic epilepsy, one that is characterized by appearance of 2 or more spontaneous epileptic seizures, separated by 24 hours, with no identified etiologic agent and with suspected genetic predisposition. It is classified as:
- genetic epilepsy: There are few breeds in which genetic testing can be carried out to detect epilepsy (which is why it is generally a disease of diagnosis by exclusion).
- Suspicion of genetic epilepsy (breeds with racial predisposition, or family history with 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) that is, patients with epileptic seizures, in whom diagnostic tests are performed, with normal results, and by review they are not typical of idiopathic epilepsy.
d) reactive seizures: those that occur as a result of poisoning, metabolic/endocrine or nutritional disorders.
Classification by type of epileptic seizures
a) Focal seizures: regional or lateralized signs / involvement of a part of the brain tissue. Types: motor (facial tremors, blinking, head shaking, repetitive movements in a limb), autonomic (dilated pupils, hypersalivation or vomiting) or behavioral-sensory (anxiety, sudden fear and restlessness). 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 progressing to generalized: in these, the patient begins 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: a neurodegenerative disease described in Beagles, Miniature Short-haired Dachshunds and Basset Hounds).
Phases of epileptic seizures
- Pródromo: just before the crisis. It can be predicted (↑anxiety, restlessness, hiding).
- Aura: initial manifestation of the seizure (stereotypes, autonomic signs, barking...); this term is no longer used in veterinary medicine since the sensations before a seizure are subjective and this cannot be assessed in animals.
- Stroke: “seizure phase”, involuntary movements/behaviours. During this phase (if any) the patient will manifest autonomic signs.
- After-shock: after the crisis. It can last from seconds to days. Sometimes it is the only thing that the owner observes. The patient may display abnormal behavior, disorientation, appetite, vomiting, blindness, compulsive gait, or even aggressive episodes.
Frequency of epileptic seizures
- specific episodes.
- Seizure clusters: presence of 2 or more seizures in a 24-hour period and between them, the neurological examination is normal.
- “Status epilepticus”: seizure lasting more than 5 minutes, or two or more seizures in a row without complete recovery of neurological normalcy between them within 24 hours.
Seizure clusters and status epilepticus are neurological emergencies.