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Luisa De Risio Neurology/Neurosurgery Unit, Centre for Small Animal Studies, Animal Health Trust, Newmarket, UK

A seizure (or ictus) has been defined as ’a transient occurrence of signs due to abnormal excessive or synchronous neuronal activity in the brain’ (Fisher et al., 2005). The clinical manifestations of a seizure are sudden and transient and depend on location of onset in the brain, patterns of propagation and a variety of other factors (see Chapter 1). Seizures can affect one or more of the following functions: sensory, motor, and autonomic activity, consciousness, emotional state, memory, cognition or behaviour (Fisher et al., 2005). The seizure (or ictus) may be preceded by a prodrome (or prodromal phase), which can be characterized by anxiety, restlessness, increased affection, withdrawal, aggressiveness, or vocalization, and by an aura, which is the initial manifestation of a seizure. The prodrome can occur hours to days before the seizure, the aura generally lasts seconds. The aura has been described in people as a subjective sensation, such as dizziness, tingling, and anxiety at the start of a seizure. In animals it may manifest as increased or decreased attention seeking, stereotypical sensory or motor behaviour (e.g. licking, pacing) or autonomic manifestations (e.g. salivating, vomiting, urinating). The ictus is the seizure itself and, in most cases, it lasts only a few minutes. The post-ictal period occurs soon after the seizure (or ictus) and may last seconds to days. Clinical manifestations include disorientation, aggressive behaviour, restlessness, pacing, lethargy, deep sleep, hunger, thirst, defecation, urination, ataxia, proprioceptive deficits and decreased or absent menace response with or without actual blindness.

Epilepsy has been defined as an enduring disorder of the brain that is characterized by recurrent seizures (Blume et al., 2001; Fisher et al., 2005). As there are many causes of chronic recurrent seizures, epilepsy is not a specific disease but rather a group of heterogeneous conditions. However, not all seizures are associated with epilepsy. For instance, a seizure can be the reaction of a normal brain to a transient insult, such as intoxication or metabolic disorder. If seizures no longer occur when the metabolic or toxic disorder resolves, the patient is not considered to have epilepsy.

A classification of seizures and epilepsies is important as clinical manifestations and aetiologies of seizures vary considerably. A standardized and uniform classification of seizure and epilepsy would allow consistency in the use of diagnostic terms, improve communication among clinicians and methods of evaluating treatment, and facilitate comparison of clinical cases and scientific studies.

Classification of seizures and epilepsies in veterinary medicine is largely based on its human counterpart and focuses on seizure phenomenology and aetiology (Schwartz-Porsche, 1994; Podell et al., 1995; Berendt and Gram, 1999; Licht et al., 2002; Podell, 2004). The main limitations of the veterinary classification are that: (i) recognition of seizure occurrence and clinical manifestations is largely dependent on the pet-owner’s observation; (ii) electroencephalographic (EEG) data are usually not available; and (iii) no agreement has been reached for a standardized terminology in veterinary medicine. Therefore, the veterinary literature on this subject is often confusing with regard to definitions and interpretations. In addition, as in human medicine, seizure classification is an ongoing process and therefore updating is necessary.

This chapter will initially present the definitions and classifications of seizure and epilepsy in human medicine that are relevant in order to understand how terminology and classification have been developed and could evolve in veterinary medicine. Subsequently the focus will be on proposed veterinary terminology and classification.