it was originally thought that focal-onset seizures with or without secondary generalization would occur only in animals with structural brain diseases (symptomatic epilepsy), focal-onset seizures have been reported also in dogs and cats with idiopathic epilepsy (Patterson et al., 2003; Berendt et al., 2009; Kuwabara et al., 2010; Pákozdy et al., 2010). In addition, the same animal can be affected by different types of seizures (e.g. focal-onset with or without secondary generalization and generalized-onset seizures) (Quesnel et al., 1997; Licht et al., 2002; Pákozdy et al., 2010). Therefore the clinical manifestations of seizures should not be used to infer the aetiologic diagnosis.
Precipitated seizures
The majority of seizures appear to occur spontaneously, however sometimes seizures may be precipitated by a variety of environmental and internal factors. In human patients, sleep deprivation, emotional stress, menstruation, missed anti-epileptic medication and concurrent illness can result in so called ‘precipitated seizures’ (Commission, 1989). Emotional stress caused by changes in the daily routine (including moving to another place or travelling), unexpected noise, sudden awakening, or an unusual event have been reported to precipitate seizures in Labrador retrievers (Heynold et al., 1997). Another study reported that anxiety, hyperactivity or stress (e.g. working under conditions with a demand for high performance) sometimes provoked seizures in 22% (11/49) of the included Belgian shepherds (Berendt et al., 2008).
Reflex seizures
Reflex seizures are seizures that can be consistently provoked by specific sensations or perceptions (Commission, 1989). The trigger is specific and the latency between trigger and seizure is short (seconds to minutes). Reflex seizure triggers in people include flickering light (usually from a television) or other visual stimuli, immersion in hot water, reading, certain sounds and eating. These stimuli are usually limited in an individual patient to a single specific stimulus or a limited number of closely related stimuli. Reflex seizures are usually generalized (although focal seizures have also been reported in association with tactile or proprioceptive stimuli) and associated with idiopathic epilepsy in humans (Commission, 1989). Seizures consistently associated with sounds (lawnmower engine), automobile rides or veterinary offices have been observed in dogs (Thomas, 2010).
Regardless of the underlying aetiology, seizures can occur as:
• Self-limiting isolated seizures: a seizure that occurs only once in a 24-h period;
• Cluster seizures: two or more seizures within 24 h with full recovery of consciousness between seizures;
• Status epilepticus: continuous seizure activity for 5 or more minutes or two or more discrete seizures within 24 h without full recovery of consciousness between seizures.
Status epilepticus and cluster seizures are neurological emergencies described in detail in Chapters 23 and 24.
Classification of seizures and epilepsies is an ongoing process in humans and veterinary neurologists should follow its development closely. Establishing a universally accepted and standardized terminology to describe ictal phenomenology would greatly help communication among veterinary clinicians and scientists and represent the foundation of further development of the veterinary classification. The veterinary classification of seizures and epilepsies will evolve as EEG and functional MRI become more widely used, new underlying aetiologies are detected, and breed-related epileptic syndromes with specific genetic mutations are identified.
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