Canine and Feline Epilepsy. Luisa De Risio
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not ‘of unknown cause’. The 1989 ILAE classification defined idiopathic epilepsies based on age at seizure onset, clinical and electroencephalographic characteristics, and a presumed genetic aetiology. The diagnosis of idiopathic epilepsy in dogs and cats is based on the age at onset (generally between 6 months and 6 years), normal interictal behaviour, physical and neurological examinations, and exclusion of metabolic, toxic and structural cerebral disorders by means of diagnostic investigations (see Chapter 6). An inherited basis, familial transmission, or a higher incidence of idiopathic epilepsy has been reported in several canine breeds (Table 6.1, Chapter 6). A genetic basis for recurrent seizures has been reported in a closed colony of laboratory cats (Kuwabara et al., 2010). The breed of these cats was not specified. The age at the time of the first seizure ranged between 4 and 12 months. General physical and neurological examinations and results of diagnostic investigations (including 1.5 Tesla MRI of the brain and CSF analysis) were all normal. All cats had focal-onset complex seizures followed by secondary generalization into tonic-clonic seizures. Based on pedigree analysis an autosomal recessive mode of inheritance was hypothesized. In the clinical setting, it is difficult to demonstrate a genetic or familial basis for recurrent seizures, particularly in cats. It is likely that several cats and some of the dogs reported to have idiopathic epilepsy in the veterinary literature actually would be better classified as having epilepsy of unknown aetiology based on the most recent ILAE proposal (Berg et al., 2010) as a genetic or familial basis was neither suspected nor confirmed in these individuals and the diagnostic investigations were not always complete. Applying the term genetic rather than idiopathic also in veterinary medicine, in analogy with the most recent ILEA proposal (Berg et al., 2010), would have the advantage of limiting its use to purebred dogs with a strongly suspected or proven genetic or familial basis for the recurrent seizures. However, this term may generate confusion as clinicians may tend to use it for purebred dogs with the typical clinical features of idiopathic epilepsy and suspected genetic aetiology as well as dogs with known genetic mutations (e.g. Epm2b gene in miniature wire-haired dachshunds with autosomal recessive progressive myoclonic epilepsy (Lafora disease), or Lgi2 gene in Lagotto Romagnolo with benign familial juvenile epilepsy) resulting in particular types of epilepsy that do not meet the typical criteria for idiopathic epilepsy (Lohi et al., 2005; Seppala et al., 2011). Therefore it may be more appropriate to continue to use the term idiopathic to indicate dogs with clinical and diagnostic features typical for idiopathic epilepsy as well as a strongly suspected or proven genetic or familial basis for the recurrent seizures. The term genetic epilepsy could be introduced as an additional category to include disorders with known genetic mutation, as recently proposed in humans (Panayiotopoulos, 2012).
While 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.
References
Abramson, C.J., Platt, S.R., Jakobs, C. et al. (2003) L-2-Hydroxyglutaric aciduria in Staffordshire bull terriers. Journal of Veterinary Internal Medicine 17, 551–556.
Barnes, H.L., Chrisman, C.L., Mariani, C.L., Sims, M. and Alleman, A.R. (2004) Clinical signs, underlying cause, and outcome in cats with seizures: 17 cases (1997-2002). Journal of American Veterinary Medical Association 225, 1723–1726.
Berendt, M. (2004) Epilepsy. In: Vite, C.H. (ed.) Braund’s Clinical Neurology in Small Animals: localization, diagnosis and treatment. Document No. A3230.0704. International Veterinary Information Service, Ithaca, New York.
Berendt, M. and Gram, L. (1999) Epilepsy and seizure classification in 63 dogs: a reappraisal of veterinary epilepsy terminology. Journal of Veterinary Internal Medicine 13, 14–20.
Berendt, M., Gredal, H. and Alving, J. (2004) Characteristics and phenomenology of epileptic partial seizures in dogs: similarities with human seizure semiology. Epilepsy Research 61, 167–173.
Berendt, M., Gullov, C.H., Christensen, S.L., Gudmundsdottir, H., Gredal, H., Fredholm, M. and Alban, L. (2008) Prevalence and characteristics of epilepsy in the Belgian shepherd variants Groenendael and Tervuren born in Denmark 1995-2004. Acta Veterinaria Scandinava 50, 51.
Berendt, M., Gullov, C.H. and Fredholm, M. (2009) Focal epilepsy in the Belgian shepherd: evidence for simple Mendelian inheritance. Journal of Small Animal Practice 50, 655–661.
Berg,