Primary epilepsy: what it is and isn't (Proceedings)
Seizures and the relationship to epilepsy
a. A seizure is the outward manifestation of a paroxysmal cerebral disorder resulting from a transitory disturbance of brain function. It occurs suddenly and stops spontaneously.
b. The clinical appearance varies with location and severity of neuronal discharge. A seizure may result in a loss or derangement of consciousness, altered behavior or psychic changes (e.g. fly-biting, tail-chasing, etc.), abnormal muscle tone and/or movement, or autonomic disturbances such as urination, defecation, salivation, dilated pupils, vomiting, or diarrhea.c. Because the external manifestation of seizures can vary considerably, any unusual involuntary phenomenon that is episodic and recurrent is a "potential" seizure disorder.
d. Areas of the brain that can result in seizures: Cerebrum, limbic system, and thalamus. Seizures can be a sign of anything from organic brain disease to genetically determined neuronal morphology/physiology that allows spontaneous depolarization.
e. The treatment and prognosis is dependent on the underlying cause of the seizure.
f. Estimates of seizure incidence are about 5.7% of all dogs and up to 1% of all cats.
a. Term is derived from the Greeks and means, "to seize upon", "take hold of".
b. A single seizure can occur in an animal for a variety of causes, but if seizures recur over a period or time, the term epilepsy is applied.
c. In the strictest sense, the term epilepsy refers to recurrent seizure from any intracranial cause, from tumors to primary (idiopathic or inherited) epilepsy. However many people use the term only in reference to primary (idiopathic or inherited) epilepsy. Recurrent seizures from metabolic causes (e.g. hypoglycemia) are not epilepsy.
d. Epilepsy: Types that have been described
1. Idiopathic: Idiopathic epilepsy is a diagnosis by elimination, i.e. we look for other causes of seizures and if we can't find any, we call the epilepsy "idiopathic". Some reserve this term for dogs that have primary epilepsy; others use it less sparingly. It is very important to aggressively search for an underlying cause before resorting to this label for epilepsy. There can be 3 tiers or levels of diagnostics that can help one be more sure of the label:
a. Reviewing age of onset of seizure activity, breed, description of seizure activity, results of hemogram/chemistry profile/UA.
b. All of the above, plus thoracic radiographs, bile acids, and specific titers based on history and examinatio
c. All of 1 and 2 in addition to spinal fluid analysis and MRI or CT of the brain, CSF titers, EEG.
2. Inherited: This form of epilepsy is caused by a mutation in a specific gene that affected dogs inherited from their parents. Certain breeds are predisposed. A few breeds have proven hereditary epilepsy, while in most it is just a strong suspicion. Some prefer to use the "idiopathic" term instead of "inherited" or "hereditary" epilepsy unless there is more genetic evidence of inheritance; thus the reason for the overlap in descriptions.
3. Primary: In order to avoid using Inherited or Idiopathic Epilepsy when there is vs. Secondary/Symptomatic Epilepsy: Primary is reserved for idiopathic/inherited epilepsy meaning that there are no overt anatomical or histopathological lesions in the brain to explain the epilepsy. Secondary or Symptomatic Epilepsy implies that the seizures are due to an identifiable neurological disorder like brain trauma, cerebral neoplasia, active or inactive encephalitis, hypoxia.
4. Cryptogenic or "probably symptomatic" epilepsy is believed to be the result of a structural lesion of the brain that is not identified.