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EPILEPTIC SEIZURES IN DOGS

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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).

It is important not to confuse epileptic seizures with other types of paroxysmal movements (dyskinesias – movement disorders) or with syncope, vestibular problems, narcolepsy/cataplexy, neuromuscular problems or pain episodes (movement disorders), among others. To try to avoid confusion, it is important to know the different phases of epileptic seizures.

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

    1. Occasional episodes.
    2. “Clusters” of seizures: presence of 2 or more seizures in a 24-hour period and between them, the neurological examination is normal.
    3. “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.

This is the second article of a series of two, in which we tell you from Ane Uriarte, what is hydrocephalus in dogs, causes of its development, how it presents itself as well as the diagnosis and clinical treatment to be performed.

Author: Ane Uriarte 

Dip ECVN, DVM, MRCVS, RCVS Recognized specialist in Neurology, EBVS, European Specialist in Veterinary Neurology Veterinary

Diagnosis of hydrocephalus in dogs

The most reliable and extensive method for the diagnosis of hydrocephalus in dogs and its cause is magnetic resonance imaging (MRI). A tomodensitometric (TM) examination will allow us to observe the dilated ventricular system without being able to provide much information regarding the reason for the dilatation or the cortical state. We must remember that many of these animals present more than one cerebral/cervical congenital malformation, and MRI is the most exhaustive way to study these.

Resonancia Magnética de Cavalier King
Magnetic Resonance of Cavalier King 1.5T MRI. Sagittal T2WI image of a Cavalier King Charles Spaniel. Hydrocephalus with Chiari-like syndrome and syringomyelia. Note the dilatation of the ventricular system with herniation of the cerebellum through the formen magnum.

 

Resonancia Magnética 2
Magnetic Resonance Imaging 2 1.5T MRI. Sagittal T2WI image of congenital hydrocephalus where the entire ventricular system is dilated.

Treatment of hydrocephalus in dogs

The definitive treatment of hydrocephalus in dogs is surgery. The problem we face is to choose the best time to bring a relevant clinical improvement to the patient, since certain animals can develop a comfortable life with little or no clinical signs or evolution.

  1. Medical treatment: The medical treatments available to reduce CSF production are few and their use does not usually improve clinical symptoms significantly: corticosteroids (anti-inflammatory doses) and diuretics. In case of seizures, antiepileptic treatment should be instituted immediately.
  2. Surgical treatment: Surgical treatment is the only treatment that will stop the clinical development, controlling ventricular enlargement and consequently cerebral degeneration. The big dilemma is: When should surgery be performed (not too early, not too late) and what type of valve should I use?
Imagen perioperatoria e imagen por tomo-densitometría
Perioperative imaging and tomo-densitometry imaging Perioperative image and computed tomo-densitometry image after ventriculo-peritoneal shunt position. Note the correct presence of the valve in the lateral ventricle.

Prognosis of hydrocephalus in dogs

In animals that are not severely affected, and only present clinical symptoms (usually seizures) at an advanced age (several years) the prognosis is generally good. These animals usually respond to antiepileptic treatment and generally do not need a ventricular shunt. In cases of rapid progressive hypertensive hydrocephalus, surgery is the only option, but in most cases the results are highly satisfactory. The problem in these cases is rather economic: the valves are expensive and will probably need revision at some point.

Shunt subcutáneo
Note the subcutaneous shunt and the extra conduit that allows the dog to grow.

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