Читать книгу Canine and Feline Epilepsy - Luisa De Risio - Страница 70

Idiopathic or primary epilepsy refers to recurrent seizures with no underlying cause other than a strongly suspected or confirmed genetic or familial basis. In this context, the term ‘idiopathic’ refers to a disorder ‘by itself’ 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.