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The terms symptomatic epilepsy and secondary epilepsy have both been used to indicate recurrent seizures caused by a known and identifiable structural forebrain disorder such as vascular, inflammatory/infectious, traumatic, anomalous/developmental, neo-plastic and degenerative diseases. The term structural epilepsy, introduced by the ILAE 2010 proposal, should be adopted also in veterinary medicine as its meaning indicates more clearly epilepsy resulting from structural forebrain disease. The term secondary is too generic and prone to misuse, indeed, it has sometimes been used in the veterinary literature to refer to seizures caused by structural forebrain disorders as well as metabolic or toxic disorders (Pákozdy et al., 2010) generating confusion when attempting study comparison. The term symptomatic is a truism as recurrent seizures (epilepsy) are the symptom in humans and the clinical sign in animals of an underlying disease.

Dogs and cats with structural epilepsy usually present with neurological signs (other than seizures) interictally. However, focal lesions in particular areas of the brain (‘clinically silent regions’), such as olfactory bulb and frontal lobes, can result in seizure activity without any other neurological signs (Foster et al., 1988; Smith et al., 1989). Aetiologies of structural epilepsy are listed in Box 3.2 and described in detail in Chapter 5.

Table 3.3. Veterinary classification of seizures and epilepsies based on underlying aetiology, parallelism with the ILAE 2010 proposed new terminology, and terminology used in this book.

Current veterinary terminology	ILAE 2010 proposed new terminology	Terminology used in this book
Reactive seizures	Metabolic	Reactive seizures
Symptomatic or secondary epilepsy	Structural epilepsy	Structural epilepsy
Probable symptomatic or cryptogenic epilepsy	Epilepsy of unknown aetiology	Cryptogenic epilepsy
Idiopathic or primary epilepsy	Genetic	Idiopathic epilepsy

Box 3.1. Aetiologies of reactive seizures.

Metabolic

Hepatic disease

congenital and acquired portosystemic shunt, microvascular dysplasia, hepatic lipidosis, neoplasia, inflammation

Renal disease

acute renal failure, end-stage chronic renal failure

Electrolyte imbalance

hypo- or hypernatraemia, hypocalcemia

Hypoglycaemia

insulin-secreting tumour, severe sepsis, iatrogenic insulin overdose

Hypoxia

Hypertension

Polycythaemia

Nutritional

Thiamine deficiency

Toxicity

Pyrethrins/ Pyrethroids, organophosphates, chlorinated hydrocarbons carbamate

Metaldehyde

Strychnine, bromathalin

Sodium monofluoroacetate (compound 1080)

Ethylene glycol

Detergents and disinfectants

Lead and other heavy metals

Poisonous plants

Mycotoxins (penitrem A, roquefortine)

Animal-related poisoning (toad, spider, bee and wasp venom)

Metronidazole (cats)

5-hydroxytryptophan

Caffeine and other methylxanthines

Amphetamine and amphetamine-like compounds

Selective serotonin reuptake inhibitors

Classification of certain disorders may be open to debate. For example, organic acidurias such as L-2-hydroxyglutaric aciduria in Staffordshire bull terriers may be classified as structural epilepsy as they result in MRI and histological changes in the brain as well as metabolic disorders as they are caused by an error of cellular metabolism, or genetic epilepsy, as the underlying genetic mutation is known (Abramson et al., 2003; Penderis et al., 2007).

Box 3.2. Aetiologies of structural epilepsy.

Vascular

Cerebrovascular disease (ischaemic, haemorrhagic)

Inflammatory/ infectious

Viral

Bacterial

Rickettsial

Protozoal

Mycotic

Parasitic

Mycoplasmosis

Algal

Granulomatous meningoencephalomyelitis

Necrotizing meningoencephalitis

Necrotizing leukoencephalitis

Other feline and canine meningoencephalitis or meningoencephalomyelitis of unknown aetiology Traumatic brain injury Anomalous and developmental

Hydrocephalus

Hydranencephaly

Porencephaly

Meningoencephalocele

Meningoencele

Exencephaly

Holoprosencephaly

Agenesis of the corpus callosum

Lissencephaly

Polymicrogyria

Cerebral neuronal heterotopias or dysplasias

Neoplastic

Primary

Meningioma

Astrocytoma (glioblastoma multiforme)

Oligodendroglioma

Gliomatosis cerebri

Ependymoma

Choroid plexus tumours

Primitive neuroectodermal tumours (neuroblastomas, medulloblastoma, gangliocytomas)

Primary CNS lymphomas

Primary CNS histiocytic sarcoma (malignant histiocytosis)

Secondary

Haemangiosarcoma

Lymphoma

Pituitary Tumours

Carcinomas/ Adenocarcinomas (mammary, prostatic, pancreatic, pulmonary)

Nasal tumours (e.g. adenocarcinoma, squamous cell carcinoma, chondrosarcoma, neuroesthesioblastoma)

Histiocytic sarcoma

Calvarial osteosarcoma and multilobulated tumour of bone (multilobulated osteochondrosarcoma)

Malignant melanoma

Others

Degenerative

Lysosomal storage diseases

Organic acidurias

Mitochondrial encephalopathies and encephalomyelopathies

Leukodystrophies

Spongy degenerations

Multisystem neuronal degeneration/abiotrophy