Seizures in cats are caused by various onsets. Cats can have reactive, primary (idiopathic) or secondary seizures. Idiopathic seizures are not as common in cats as in dogs however a recent study conducted showed that of 91 feline seizures, 25% were suspected to have idiopathic epilepsy. In the same group of 91 cats, 50% were secondary seizures and 20% reactive.

Idiopathic epilepsy does not have a classification due to the fact there are no known causes of these seizures, however both reactive and symptomatic secondary epilepsy can be placed into classifications.

The mortality rate ranges from 3–7% in a mean follow up period of 8.5 to 9.7 years. Death is often related to accidents.

Genetics may play a role in the risk that a person will develop PTE; people with the ApoE-ε4 allele may be at higher risk for PTE. The haptoglobin Hp2-2 allele may be another genetic risk factor, possibly because it binds hemoglobin poorly and thus allows more iron to escape and damage tissues. However, most studies have found that having family members with epilepsy does not significantly increase the risk of PTS, suggesting that genetics are not a strong risk factor.

The more severe the brain trauma is, the more likely a person is to suffer late PTE. Evidence suggests that mild head injuries do not confer an increased risk of developing PTE, while more severe types do. In simple mild TBI, the risk for PTE is about 1.5 times that of the uninjured population. By some estimates, as many as half of sufferers of severe brain trauma experience PTE; other estimates place the risk at 5% for all TBI patients and 15–20% for severe TBI. One study found that the 30-year risk of developing PTE was 2.1% for mild TBI, 4.2% for moderate, and 16.7% for severe injuries, as shown in the chart at right.

Panayiotopoulos syndrome probably affects 13% of children aged 3 to 6 years who have had 1 or more afebrile seizures and 6% of such children in the 1- to 15-year age group. All races and both sexes are affected.

Panayiotopoulos syndrome is remarkably benign in terms of its evolution. The risk of developing epilepsy in adult life is probably no more than of the general population. Most patients have one or 2-5 seizures. Only a third of patients may have more than 5 seizures, and these may be frequent, but outcome is again favorable. However, one fifth of patients may develop other types of infrequent, usually rolandic seizures during childhood and early teens. These are also age-related and remit before the age of 16 years. Atypical evolutions with absences and drop attacks are exceptional. Children with pre-existing neurobehavioral disorders tend to be pharmacoresistant and have frequent seizures though these also remit with age.

Formal neuropsychological assessment of children with Panayiotopoulos syndrome showed that these children have normal IQ and they are not on any significant risk of developing cognitive and behavioural aberrations, which when they occur they are usually mild and reversible. Prognosis of cognitive function is good even for patients with atypical evolutions.

However, though Panayiotopoulos syndrome is benign in terms of its evolution, autonomic seizures are potentially life-threatening in the rare context of cardiorespiratory arrest.

LGS is seen in approximately 4% of children with epilepsy, and is more common in males than in females. Usual onset is between the ages of three and five. Children can have no neurological problems prior diagnosis, or have other forms of epilepsy. West syndrome is diagnosed in 20% of patients before it evolves into LGS at about 2 years old.

Both medication and drug overdoses can result in seizures, as may certain medication and drug withdrawal. Common drugs involved include: antidepressants, antipsychotics, cocaine, insulin, and the local anaesthetic lidocaine. Difficulties with withdrawal seizures commonly occurs after prolonged alcohol or sedative use, a condition known as delirium tremens.

A number of measures have been attempted to prevent seizures in those at risk. Following traumatic brain injury anticonvulsants decrease the risk of early seizures but not late seizures.

In those with a history of febrile seizures, medications (both antipyretics and anticonvulsants) have not been found effective for prevention. Some, in fact, may cause harm.

There is no clear evidence that antiepileptic drugs are effective or not effective at preventing seizures following a craniotomy, following subdural hematoma, after a stroke, or after subarachnoid haemorrhage, for both people who have had a previous seizure, and those who have not.

The cause of FIRES is not known. It does not happen twice in the same family, but the medical community does not know if it is genetic. It happens in boys more than girls. After the initial status, life expectancy is not affected directly. Issues such as overdose of medications or infections at a food tube site are examples of things that would be secondary to the status.

Generalized epilepsy, also known as primary generalized epilepsy or idiopathic epilepsy, is a form of epilepsy characterised by generalised seizures with no apparent cause. Generalized seizures, as opposed to focal seizures, are a type of seizure that impairs consciousness and distorts the electrical activity of the whole or a larger portion of the brain (which can be seen, for example, on electroencephalography, EEG).

Generalized epilepsy is "primary" because the epilepsy is the originally diagnosed condition itself, as opposed to "secondary" epilepsy, which occurs as a symptom of a diagnosed condition.

Most generalized epilepsy starts during childhood. While some patients outgrow their epilepsy during adolescence and no longer need medication, in others, the condition remains for life, thereby requiring lifelong medication and monitoring.

West syndrome is a triad of developmental delay, seizures termed infantile spasms, and EEG demonstrating a pattern termed hypsarrhythmia. Onset occurs between three months and two years, with peak onset between eight and 9 months. West syndrome may arise from idiopathic, symptomatic, or cryptogenic causes. The most common cause is tuberous sclerosis. The prognosis varies with the underlying cause. In general, most surviving patients remain with significant cognitive impairment and continuing seizures and may evolve to another eponymic syndrome, Lennox-Gastaut syndrome. It can be classified as idiopathic, syndromic, or cryptogenic depending on cause and can arise from both focal or generalized epileptic lesions.

Consistent risk factors include:

- Severity of seizures, increased refractoriness of epilepsy and presence of generalized tonic-clonic seizures: the most consistent risk factor is an increased frequency of tonic–clonic seizures.

- Poor compliance. Lack of therapeutic levels of anti-epileptic drugs, non-adherence to treatment regimens, and frequent changes in regimens are risk factors for sudden death.

- Young age, and early age of seizures onset.

- Male gender

- Poly-therapy of epilepsy. It remains unclear whether this is an independent risk factor or a surrogate marker for severity of epilepsy.

- Being asleep during a seizure is likely to favour SUDEP occurrence.

It is still unknown which bio-chemical mechanisms lead to the occurrence of West syndrome. It is conjectured that it is a malfunction of neurotransmitter function, or more precisely, a malfunction in the regulation of the GABA transmission process. Another possibility being researched is a hyper-production of the Corticotropin-releasing hormone (CRH). It is possible that more than one factor is involved. Both hypotheses are supported by the effect of certain medications used to treat West syndrome.

Cases of epilepsy have been historically divided into three different groups: symptomatic, cryptogenic, and unknown. The International League Against Epilepsy (ILAE) recommended in 2011 to abandon these terms for reasons of clarity and instead try to place individual cases into one of the following 3 groups: genetic, structural/metabolic, and unknown. The new terms are more immediately clear in their meaning, except that the structural and metabolic group includes cases that have a genetic component that does not always directly lead to the condition. Only the genetic grouping has a known direct genetic cause. "Unknown" cases may be of "unknown" genetic, structural, metabolic, or other unknown cause.

The old terminology was defined by the ILAE as follows:

- symptomatic: the epilepsy is the consequence of a known or suspected disorder of the central nervous system.

- cryptogenic: this refers to a disorder whose cause is hidden or occult. Cryptogenic epilepsies are presumed to be symptomatic.

- idiopathic: there is no underlying cause other than a possible hereditary predisposition.

The remainder of this section will refer to the older terminology.

It is not possible to make a generalised prognosis for development due to the variability of causes, as mentioned above, the differing types of symptoms and cause. Each case must be considered individually.

The prognosis for children with idiopathic West syndrome are mostly more positive than for those with the cryptogenic or symptomatic forms. Idiopathic cases are less likely to show signs of developmental problems before the attacks begin, the attacks can often be treated more easily and effectively and there is a lower relapse rate. Children with this form of the syndrome are less likely to go on to develop other forms of epilepsy; around two in every five children develop at the same rate as healthy children.

In other cases, however, treatment of West syndrome is relatively difficult and the results of therapy often dissatisfying; for children with symptomatic and cryptogenic West syndrome, the prognosis is generally not positive, especially when they prove resistant to therapy.

Statistically, 5 out of every 100 children with West syndrome do not survive beyond five years of age, in some cases due to the cause of the syndrome, in others for reasons related to their medication. Only less than half of all children can become entirely free from attacks with the help of medication. Statistics show that treatment produces a satisfactory result in around three out of ten cases, with only one in every 25 children's cognitive and motoric development developing more or less normally.

A large proportion (up to 90%) of children suffer severe physical and cognitive impairments, even when treatment for the attacks is successful. This is not usually because of the epileptic fits, but rather because of the causes behind them (cerebral anomalies or their location or degree of severity). Severe, frequent attacks can (further) damage the brain.

Permanent damage often associated with West syndrome in the literature include cognitive disabilities, learning difficulties and behavioural problems, cerebral palsy (up to 5 out of 10 children), psychological disorders and often autism (in around 3 out of 10 children). Once more, the cause of each individual case of West syndrome must be considered when debating cause and effect.

As many as 6 out of 10 children with West syndrome suffer from epilepsy later in life. Sometimes West syndrome turns into a focal or other generalised epilepsy. Around half of all children develop Lennox-Gastaut syndrome.

Temporal lobe epilepsy (TLE) is not a classic syndrome but mentioned here because it is the most common epilepsy of adults. It is a symptomatic localization-related epilepsy and in most cases the epileptogenic region is found in the midline (mesial) temporal structures (e.g., the hippocampus, amygdala, and parahippocampal gyrus). Seizures begin in late childhood and adolescence. Most of these patients have focal seizures sometimes preceded by an aura, and some TLE patients also have secondary generalized tonic-clonic seizures. Often seizures do not sufficiently respond to medical treatment with anticonvulsants and epilepsy surgery may be considered.

Chemotherapy medication, for example, fludarabine can cause a

permanent severe global encephalopathy. Ifosfamide can cause

a severe encephalopathy (but it can be reversible with stop using the drug and the use of methylene blue). Bevacizumab and other anti–vascular endothelial growth factor medication can cause posterior reversible encephalopathy syndrome.

No single cause of OS has been identified. In most cases, there is severe atrophy of both hemispheres of the brain. Less often, the root of the disorder is an underlying metabolic syndrome. Although it was initially published that no genetic connection had been established, several genes have since associated with Ohtahara syndrome. It can be associated with mutations in "ARX", "CDKL5", "SLC25A22", "STXBP1", "SPTAN1", "KCNQ2", "ARHGEF9", "PCDH19", "PNKP", "SCN2A", "PLCB1", "SCN8A", and likely others.

Treatment outlook is poor. Anticonvulsant drugs and glucocorticoid steroids may be used to try to control the seizures, but their effectiveness is limited. Most therapies are related to symptoms and day-to-day living.

Early myoclonic encephalopathy (EME) is an epilepsy syndrome where myoclonic seizures develop in the neonatal period. After several months, the seizure pattern may develop to infantile spasms (West syndrome). Various genetic and metabolic disorders are responsible. The seizures are resistant to treatment. The neurology is very abnormal and patients often do not live beyond one year.

The lack of generally recognized clinical recommendations available are a reflection of the dearth of data on the effectiveness of any particular clinical strategy, but on the basis of present evidence, the following may be relevant:

- Epileptic seizure control with the appropriate use of medication and lifestyle counseling is the focus of prevention.

- Reduction of stress, participation in physical exercises, and night supervision might minimize the risk of SUDEP.

- Knowledge of how to perform the appropriate first-aid responses to seizure by persons who live with epileptic people may prevent death.

- People associated with arrhythmias during seizures should be submitted to extensive cardiac investigation with a view to determining the indication for on-demand cardiac pacing.

- Successful epilepsy surgery may reduce the risk of SUDEP, but this depends on the outcome in terms of seizure control.

- The use of anti suffocation pillows have been advocated by some practitioners to improve respiration while sleeping, but their effectiveness remain unproven because experimental studies are lacking.

- Providing information to individuals and relatives about SUDEP is beneficial.

There are many types of encephalopathy. Some examples include:

- Mitochondrial encephalopathy: Metabolic disorder caused by dysfunction of mitochondrial DNA. Can affect many body systems, particularly the brain and nervous system.

- Glycine encephalopathy: A genetic metabolic disorder involving excess production of glycine.

- Hepatic encephalopathy: Arising from advanced cirrhosis of the liver.

- Hypoxic ischemic encephalopathy: Permanent or transitory encephalopathy arising from severely reduced oxygen delivery to the brain.

- Static encephalopathy: Unchanging, or permanent, brain damage.

- Uremic encephalopathy: Arising from high levels of toxins normally cleared by the kidneys—rare where dialysis is readily available.

- Wernicke's encephalopathy: Arising from thiamine (B) deficiency, usually in the setting of alcoholism.

- Hashimoto's encephalopathy: Arising from an auto-immune disorder.

- Hypertensive encephalopathy: Arising from acutely increased blood pressure.

- Chronic traumatic encephalopathy: Progressive degenerative disease associated with multiple concussions and other forms of brain injury.

- Lyme encephalopathy: Arising from Lyme disease bacteria, including "Borrelia burgdorferi".

- Toxic encephalopathy: A form of encephalopathy caused by chemicals, often resulting in permanent brain damage.

- Toxic-Metabolic encephalopathy: A catch-all for brain dysfunction caused by infection, organ failure, or intoxication.

- Transmissible spongiform encephalopathy: A collection of diseases all caused by prions, and characterized by "spongy" brain tissue (riddled with holes), impaired locomotion or coordination, and a 100% mortality rate. Includes bovine spongiform encephalopathy (mad cow disease), scrapie, and kuru among others.

- Neonatal encephalopathy (hypoxic-ischemic encephalopathy): An obstetric form, often occurring due to lack of oxygen in bloodflow to brain-tissue of the fetus during labour or delivery.

- Salmonella encephalopathy: A form of encephalopathy caused by food poisoning (especially out of peanuts and rotten meat) often resulting in permanent brain damage and nervous system disorders.

- Encephalomyopathy: A combination of encephalopathy and myopathy. Causes may include mitochondrial disease (particularly MELAS) or chronic hypophosphatemia, as may occur in cystinosis.

- Creutzfeldt–Jakob disease (CJD; transmissible spongiform encephalopathy).

- HIV encephalopathy (encephalopathy associated with HIV infection and AIDS, characterized by atrophy and ill-defined white matter hyperintensity).

- Sepsis-associated encephalopathy (this type can occur in the setting of apparent sepsis, trauma, severe burns, or trauma, even without clear identification of an infection).

- Epileptic encephalopathies:

- Early infantile epileptic encephalopathy (acquired or congenital abnormal cortical development).

- Early myoclonic epileptic encephalopathy (possibly due to metabolic disorders).

Ohtahara syndrome (OS), also known as early infantile epileptic encephalopathy with burst-suppression (EIEE), is a progressive epileptic encephalopathy. The syndrome is outwardly characterized by tonic spasms and partial seizures, and receives its more elaborate name from the pattern of burst activity on an electroencephalogram (EEG). It is an extremely debilitating progressive neurological disorder, involving intractable seizures and severe mental retardation. No single cause has been identified, although in many cases structural brain damage is present.

Though there is limited evidence, outcomes appear to be relatively poor with a review of outcome studies finding that two thirds of PNES patients continue to experience episodes and more than half are dependent on social security at three-year followup. This outcome data was obtained in a referral-based academic epilepsy center and loss to follow-up was considerable; the authors point out ways in which this may have biased their outcome data. Outcome was shown to be better in patients with higher IQ, social status, greater educational attainments, younger age of onset and diagnosis, attacks with less dramatic features, and fewer additional somatoform complaints.