Epilepsy:

• It is a condition where there are paroxysmal, self-limited functional cerebral disturbances characterized by abnormal electrical activity of brain.
• It leads to signs known as ‘seizure’, ‘fits’ or ‘convulsion’.
• Each attack is characterized by sudden loss of consciousness.
• It is most common chronic neurological disorder in veterinary medicine and affects upto 1% dogs and 2% cats in general population.
• Seizures are clinical manifestations of excess and hypersynchronous electrical activity in the cerebral cortex.

Classification of Epilepsy:

1. According to Etiology
2. According to Nature of Fit (Clinical)

1. According to Etiology:

Based on etiology, it is of two types:

1. Idiopathic epilepsy:

• In this type there is no definite causes.
• In majority of cases, hereditary history is present.
• There may be some kind of metabolic disturbances.
• It is genetical and age dependent.
• Certain breeds are predisposed to this type of epilepsy.

1. Symptomatic epilepsy:

• this type of epilepsy denotes physical, physiological and inflammatory derangements.
• It is common in cats.
• This type of epilepsy is result of one or more identifiable structural lesion of the brain.

1. According to Nature of Fit (Clinical):

Based on nature of fit, it is of two types:

1. Generalized epilepsy:

• In this type of epilepsy, abnormal electrical discharges spread all over the brain.
• It reflects involvement of both hemisphere of cerebral cortex.
• It is of further 3 types:
  • Grand mal (Major epilepsy)
  • Petit-mal (Minor epilepsy)
  • Status epilepticus

1. Focal epilepsy:

• In this type, abnormal electrical discharge is localized to a particular part of brain (cerebral hemisphere).
• It may be:
  • Temporal lobe epilepsy
  • Jacksonian epilepsy
  • Myoclonic epilepsy
  • Akinetic attack or focal fits

Etiology:

• Traumatic injury of cranium
• Degenerative changes in brain
• Congenital malformation of brain
• Space occupying lesion (cyst, tumor, abscess)
• Meningitis, encephalitis
• Otitis media
• Metabolic disturbances: Diabetes mellitus, uremia, hepatic coma, alkalosis, hypocalcemia)
• Fever- febrile convulsion, febrile fit
• Cardiac disorder- aortic stenosis, pulmonary stenosis, myocardial infarction, etc
• Canine distemper, Cryptococcosis
• Round worm infestation, tapeworm infestation
• Toxin- Bait, mycotoxin, spoiled feeds
• Hypoglycaemia
• Hydrocephalus

Stages of epilepsy:

1. Stage of aura:

• It is the first stage. It is warming signal indicating that the fit is coming.
• The animal shows the expression that some danger is coming
• It persists for few seconds.
• Animal remains conscious but doesnot possess voluntary power.
• Type of aura depends on site of abnormal electrical discharge. It may include:
  • Motor aura: twitching and convulsion of angle of mouth
  • Sensory aura: peculiar sensation on body
  • Visual aura: visual hallucination, vacant look

1. Stage of prodromal (unconsciousness):

• It follows the stage of aura
• Animal becomes still and unconscious.

• Stage of ictus (convulsion):
• It has got two phases; tonic phase and clonic phase
• In tonic phase, suddenly the muscles of whole body are thrown into tonic spasm and animal will fall on ground.
• This phase may be characterized by deviation of eyes, epileptic cry, temporary stoppage of respiration, cyanotic condition, rapid pulse and abnormalities in limbs.
• In clonic phase, there is convulsion of all muscle groups including limbs. This may be characterized by pedaling movements.
• Initially clonic convulsion occurs at regular frequency but gradually becomes longer at intervals and ultimately ends with final jerk and passes into stage of flaccid coma.
• Ictus phase is characterized by;
  • Tongue biting
  • Hypersalivation (blood stained froth from mouth and nostril)
  • Urination
  • Defecation
  • Pupillary dilatation
• It may last from few seconds to a few minutes

1. Stage of post-ictus (post-convulsive):

• Following clonic phase, animal regains its consciousness but not the full functions of nervous control.
• It may show flaccidity of muscles, depression, fatigueness, incoordination of gait and blindness.
• It may remain from few seconds to few days.

Clinical Signs:

• Stiffening of neck and legs
• Stumbling and falling over
• Uncontrollable chewing, drooling
• Paddling of limbs
• Loss of bladder control, defecation
• Vocalizing
• Violent shaking and trembling
• It lasts for about 30-90 seconds and animal is typically unaware of its surroundings

Diagnosis:

• Based on history of traumatic injury or other metabolic disturbances
• Based on clinical signs
• Based on normal neurologic examination
• Brain MRI and EEG
• Spinal fluid analysis

Differential Diagnosis:

Causes within 6 months of age:

• Juvenile epilepsy: Unknown etiology. Young dogs used to suffer. Cocker spaniel suffers the most. Phenobarbital therapy may give satisfactory result.
• Inflammation induced epilepsy: Canine distemper, Neospora caninum, fungus, bacteria and coli may cause epileptic seizure.
• Toxin induced epilepsy: Bait, mycotoxin, spoiled feeds may cause epilepsy. Diazepam @0.5-1 mg/kg, IV may be of help
• Traumatic epilepsy: Brain trauma causes epileptic seizure.
• Hypoglycaemic epilepsy: Abrupt fall in blood glucose level may produce epilepsy in toy breeds of dog.
• Hydrocephalus predisposed epilepsy
• Hepatic encephalopathy induced epilepsy: Generalized tonoclonic seizure may be the feature

Causes within 6 months- 5 years of age:

• Idiopathic- Genetic epilepsy
• Infectious: Viral, Rickettsial, Parasitic, Bacterial, Protozoal, Fungal
• Non-infectious: Granulomatosis, Immune-mediated, Breed specific
• Tumors

Causes in more than 5 years of age:

• Symptomatic causes: Metabolic disturbances, degenerative changes in brain, congenital malformation of brain
• Inflammatory disease
• Thalamocortical tumour
• Encephalopathy
• Beta cell tumour

Treatment:

• Except with head trauma, starting of antiepileptic drugs (AED) is not recommended.
• Patients should be started with AEDs in case of status epilepticus or cluster seizures (>1 seizure, q24h) or if long-term control is necessary (i.e. 1 seizure q4-6 weeks)
• As in any emergency, airway, breathing and circulatory disturbances should be corrected first.
• First line of drug for seizure is typically benzodiazepines; diazepam or midazolam administered IV or double dose. Diazepam @ 0.5-1 mg/kg/IV
• If seizure persists, phenobarbital is administered @2-5 mg/kg, BID. PB is added to DZ @2-10 mg/hour
• Status epilepticus requires rapidly increasing blood levels or loading the patient with a long-term AED by injection to rapidly reach therapeutic blood levels; phenobarbital is often the first choice
• Propofol is given to patients that fails to respond to benzodiazepines or as first line agent to arrest status epilepticus in patients with post-stroke seizure (PSS).
• Levetiracetam is immediately effective with few adverse effects and has become widely used in veterinary medicine.
• Bromides (potassium bromide, injectable sodium bromide) may also be administered as long-term AEDs in dogs only.

Common Medications for Treatment of Epilepsy:

Some Guidelines for Therapy:

• Maximum dose should be given initially
• No drugs should be withdrawn suddenly.
• Replacing of one drug by other should not be done overnight but be done gradually.
• Drug should be continued for few days after the last attack.
• More dose may be given in the evening rather than morning.

Drugs contraindicated in epilepsy: Phenothiazine derivative tranquilizer e.g., Chlorpromazine (Largactil), Trifluopromazine (Siquil), etc. are not to be used against epilepsy as they activate the epileptic brain.

Dog Breeds Predisposed to Epilepsy: