Seizures

By | 2011-06-27

1. What is a seizure?

A seizure is a paroxysmal, transitory disturbance of brain function that has sudden onset, ceases spontaneously, and is likely to recur. Although most veterinarians call the resulting effects (e.g., jerky movements, staring) a “seizure,” the seizure is the neuronal event itself. The observable manifestation is called “seizure activity.”

2. Why are seizures an important emergency?

Something is interfering with normal functioning of a group of neurons. The hyperactivity of the neurons causes a build-up of metabolic byproducts, resulting in a harmful effect on the neurons. Neurons depend on aerobic metabolism. When the need for oxygen outstrips the availability, the neuron is injured. If this situation is prolonged, cell death results.

3. Describe the general pathophysiology of seizures.

Seizures are the result of disturbances in normal electrical activity in the brain. Anything that alters neuronal function may lead to a lower threshold of excitability and spontaneous depolarization. If the depolarization wave spreads to other areas of the brain or the entire nervous system, seizures result. The basic pathophysiologic processes that result in seizures are excessive cellular excitation and loss of cellular inhibition.

4. How are seizures classified?

In a study of nonreferral seizures, 53 etiologic diagnoses were found. The seizures were classified as follows:

Primary epileptic seizure (idiopathic or without a definable cause) – 44%

Secondary epileptic seizure (identifiable intracranial cause) – 46%

5. What is the difference between focal and generalized seizures?

Focal seizures remain localized to one body region. They may become generalized and are more often associated with structural brain disease.

Generalized seizures affect the entire body simultaneously.

6. What is the most common seizure in animals?

Generalized, tonic-clonic seizures.

7. Define status epilepticus.

Status epilepticus is a condition characterized by an epileptic seizure that is so frequent or so prolonged as to create a fixed or lasting condition. In veterinary medicine, status epilepticus traditionally has been defined as a seizure lasting 30 minutes or longer. This does not mean that one waits 30 minutes to institute therapy! A practical, operational definition for veterinarians for status epilepticus is either continuous seizure activity lasting at least 5 minutes or 2 or more seizures with poor or incomplete recovery between seizures.

8. Give examples of bizarre behaviors that may be manifestations of seizure disorders in animals.

• Fly-biting

• Tail-biting

• Flank-sucking

9. What are the common causes of seizures?

1. Idiopathic epilepsy
2. Metabolic disease

Hypoglycemia

• Hypoxia

• Hypocalcemia

• Renal or hepatic disease

Hyperkalemia

3. Infection

• Feline infectious peritonitis

Rabies

Canine distemper

• Other fungal or bacterial causes

• Toxoplasmosis

4. Inflammation (noninfectious)

• Trauma

• Granulomatous meningoencephalitis

5. Neoplasia
6. Malformation

• Hydrocephalus

• Lissencephaly

• Lysosomal storage disorders

7. Toxicities

10. How can the signalment aid in the initial diagnosis of seizures?

1. Age

• < 1 year

Congenital: hydrocephalus, lissencephaly

Inflammatory: meningitis

Metabolic: portosystemic shunts

Toxic: lead, ethylene glycol, organophosphates

• 1-5 years: primary epilepsy

• > 5 years Neoplasia

Metabolic: hepatic or renal dysfunction, hyperadrenocorticism, hypoadrenocorticism

2. Breed

• Beagle, German shepherd, Keeshond, collie, Belgian Tervuren: genetic or inherited primary epilepsy

• Miniature/toy breeds: hypoglycemia

• Yorkshire terrier, schnauzer: portosystemic shunts

3. Sex: epilepsy affects males more often than females.

11. Is a neurologic examination helpful in animals with seizures?

Certainly. You need to examine carefully the cranial nerves, comparing right with left and completing the examination with assessment of motor function and reflexes of the extremities. Idiopathic seizures are not commonly associated with interictal neurologic deficits. The caveat is that some dogs may have neurologic deficits in the postictal period that last for days after the seizure. Metabolic causes of seizures may be associated with persistent neurologic deficits, which are most commonly symmetrical.

12. What diagnostic testing should be done to localize the lesion?

• Laboratory studies: complete blood count, serum biochemical profile, urinalysis, and heart-worm or FELV/FIV testing

• Electrocardiogram

• Specialized testing: blood lead, ethylene glycol

• Radiography: thoracic, abdominal

• Computed tomography and magnetic resonance imaging

13. How should status epilepticus be treated initially?

Status epilepticus is a true emergency and must be managed quickly. The ABCs (airway, breathing, circulation) must be attended to immediately. Supplemental oxygen should be supplied. If the airway and breathing are compromised, an endotracheal tube is inserted and ventilation is assisted. Venous access should be established and crystalloid fluids administered. If the severity of the seizure or the size of the animal prevents quick venous access, diazepam may be administered rectally at 0.5-2 mg/kg. Intravenous diazepam is delivered to effect (up to 2 mg/kg). If diazepam is not effective, phenobarbital is administered intravenously up to to 16 mg/kg. You may not see an effect with phenobarbital for 20 minutes if the animal has not taken the drug previously. Constant-rate infusions of phenobarbital may be given at 2-4 mg/kg/hr. Body temperature may be quite high if the patient has been seizing for more than 10 minutes. Seizure control and intravenous fluids are usually adequate to correct hyperthermia. Use caution if cold water bathing is necessary (temperature > 105°F after 10 min); hypothermia is frequently a problem in patients requiring long-term sedation.

14. What are the advantages of using per rectum diazepam to control seizures at home?

Advantages include the ability to reduce the number of cluster seizure events, improved overall success in therapeutic control of idiopathic epilepsy, and fostering of a better home environment for the epileptic dog and its owner through the reduction of total seizure activity, yearly emergency clinic costs, and owner anxiety.

15. How are seizures treated pharmacologically?

Drug Half-Life Metabolism Dosage Interactions Side Effects, Toxicity
Diazepam 3.2 hr Hepatic 0.5-2 mg/kg IV or rectally CNS depression
Phenobarbital 47-74 hr (dogs) 34-43 hr (cats) Renal excretion Up to 16 mg/kg IV; 2-4 mg/kg orally 2 times/ day CNS depression / excitability; polyuria, polydipsia, polyphagia
Primidone 10-14 hr Hepatic 15-30 mg/kg/day divided into 3 doses Sedation, polyuria, polydipsia, nystagmus, anorexia, hepatotoxicity, dermatitis
Phenytoin 4hr Hepatic 35-50 mg/kg 3 times/ day Sedation, polyuria, polydipsia, nystagmus, tachycardia, hepatopathy, coagulation defects; toxic to cats
Clonazepam 1.4 hr Hepatic 0.5 mg/kg orally 2 or 3 times/day Sedation: after prolonged treatment may see withdrawal signs
Cloazepate 41 hr (humans) 2 mg/kg orally 2 times/ day ?
Potassium bromide 25 days Renal excretion Loading dose = 400-600 mg/kg orally over 30-60 min; 20-60 mg/kg/ day orally or divided inti 2 doses Vomiting, sedation, diarrhea, constipation

CNS = central nervous system.

16. What is a toxic blood level of phenobarbital?

40 mg/ml.

17. What are the complications of status epilepticus?

Hyperthermia, neurologic deficits (inability to walk normally, central blindness, and tremors), hypoglycemia, rhabdomyolysis, acidosis, hypertension, cardiac dysrhythmias, and death.

18. Which causes of seizure activity result in the poorest prognosis for dogs?

Granulomatous meningoencephalitis, loss of seizure control after 6 hours of hospitalization, or the development of partial status epilepticus.

19. Other than intravenous and intrarectal, what other route may be used for administration of diazepam during seizure?

Diazepam is absorbed rapidly and efficiently following intranasal administration. Plasma concentrations match or exceed the therapeutic concentration (300 ug/L). This technique may be useful when seizures in dogs are treated by owners or when IV access is not readily available. Be careful! You can receive a severe bite wound from the dog during this procedure.