Canine and Feline Epilepsy. Luisa De Risio
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Atypical absence seizures occur in patients with cryptogenic or structural generalized epilepsies and are often associated with slow spike-wave complexes of 1.5–2.5 Hz. Motor manifestations are more pronounced in patients with atypical absence seizures than in those with typical absence seizures.
Table 3.1. Comparison of major changes between the 1981 and 1989 Classification and Terminology and the newly proposed Classification and Terminology (Commission, 1981, 1989; Berg et al., 2010).
| ILAE 1981 and 1989 | ILAE 2010 |
| Generalized seizures are those in which the first clinical and electroencephalographic changes indicate initial involvement of both cerebral hemispheres. | Generalized seizures are conceptualized as originating at some point within and rapidly engaging bilaterally distributed networks. Such bilateral networks can include cortical and subcortical structures, but do not necessarily include the entire cortex. |
| Focal seizures (previously termed as partial) are those in which the first clinical and electroencephalographic changes indicate initial activation of a system of neurons limited to a part of one cerebral hemisphere. | Focal seizures are conceptualized as originating at some point within networks limited to one hemisphere. They may be discretely localized or more widely distributed. Focal seizures may originate in subcortical structures. |
| Idiopathic epilepsy: there is no underlying cause other than a possible hereditary predisposition. Idiopathic epilepsies are defined by age-related onset, clinical and electroencephalographic characteristics, and a presumed genetic aetiology. | Genetic epilepsy: the epilepsy is, as best as understood, the direct result of a known or presumed genetic defect(s) in which seizures are the core symptom of the disorder. This attribution must be supported by specific forms of evidence (e.g. specific molecular genetic studies or family studies). |
| Structural epilepsy: this type of epilepsy is the consequence of a known or suspected disorder of the central nervous system. | Structural and metabolic epilepsy: this type of epilepsy is the secondary result of a distinct structural or metabolic condition. These structural or metabolic disorders may be of acquired or genetic origin (as is the case for malformations of cortical development and certain metabolic disorders). |
| Cryptogenic (probable structural) epilepsy: this refers to a disorder whose cause is hidden or occult. Cryptogenic epilepsies are presumed to be structural. | Unknown epilepsy: the nature of the underlying cause is as yet unknown; it may have a fundamental genetic basis (e.g. a previously unrecognized channelopathy) or it may be the consequence of an unrecognized structural or metabolic disorder not yet identified. |
The 1981 classification subdivided focal seizure types into: complex (with impairment of consciousness), simple (without impairment of consciousness) and secondarily generalized (when the initially focal ictal event progresses to involvement of the entire body resulting in a generalized seizure) (Commission, 1981). The most recently proposed classification (Berg et al., 2010) recommends to abandon this terminology (simple, complex, secondarily generalized) and to describe focal seizure semiology accurately, including impairment of consciousness/awareness, when recognized, and localization and progression of ictal events.
The most recently proposed classification of seizure and epilepsies (Berg et al., 2010) has been met with considerable dissatisfaction from several expert epileptologists and therefore the previous ILAE classifications are likely to continue to be used until a more widely accepted proposal has been developed (Panayiotopoulos, 2011, 2012). Among the criticisms to the ILAE 2010 proposal (Berg et al., 2010) the comments that are most relevant to the current veterinary classification involve:
• The need to maintain, although update, a specific classification of focal seizures rather than recommend to abandon the previous classification and use only a description of the clinical manifestations (Panayiotopoulos, 2011);
• The aetiologic classification of seizures and epilepsies should remain unchanged. The terms ‘idiopathic’, ‘symptomatic’ and ‘cryptogenic’ should not be abandoned, although their correct definition should be reiterated. The term ‘genetic’ should be introduced, not to replace ‘idiopathic’ but to represent a new category in addition to the other three in a revised classification of epilepsies (Panayiotopoulos, 2012).
Classification of Seizures and Epilepsies in Veterinary Medicine
The following classification of canine and feline seizures (Tables 3.2 and 3.3) is largely based on the ILAE classifications (mainly Commission, 1981, 1989; Engel, 2001, 2006) and on selected veterinary literature (Schwartz-Porsche, 1994; Berendt and Gram, 1999; Licht et al., 2002; Berendt, 2004; Podell, 2004; Thomas, 2010). The parallelism with the ILAE 2010 proposed new terminology (Berg et al., 2010) is indicated in parentheses where appropriate in Table 3.2, in a specific column in Table 3.3 and also discussed in the text.
Veterinary classification of seizures based on clinical manifestations
Generalized-onset seizures
The initial clinical manifestations of generalized-onset seizures indicate more than minimal involvement of both cerebral hemispheres. The motor manifestations begin bilaterally and are often symmetrical. An alteration in consciousness frequently occurs at some stage during ictus. The term ‘primary generalized’ has sometimes been used in the veterinary literature to describe generalized-onset seizures and to differentiate them from secondarily generalized focal (partial) seizures. In this case the term primary does not refer to seizure aetiology, but to the fact that the initial clinical manifestations reflect involvement of both cerebral hemispheres simultaneously from the onset of the seizure.
GENERALISED-ONSET TONIC-CLONIC SEIZURE. The most common type of generalized-onset seizure in dogs is the tonic-clonic seizure (formerly called grand mal seizure) (Berendt and Gram, 1999; Licht et al., 2002). A prodromal phase and aura are not always recognized by the owner. Their duration and clinical manifestations are variable. The prodromal phase can last hours to days and it is commonly characterized by restlessness, anxiety or reluctance to perform normal activities. The aura 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 ictal phase of a tonic-clonic seizure is characterized by sustained contraction of all muscles resulting in rigid extension of the limbs and opisthotonos, usually lasting 10 to 60 s (tonic phase). The animal falls on its side and often loses consciousness (defined as attentiveness or responsiveness to the owner and other external stimuli). Breathing is often irregular or absent, and cyanosis is common. The tonic phase is followed by the clonic phase, which is characterized by rhythmic muscular contractions resulting in uncoordinated, purposeless, jerking movements of the limbs and chewing movements. Automatisms such as running or paddling movements of the limbs commonly occur. The clonic phase may alternate with tonic activity. Autonomic manifestations, such as hypersalivation, urination, defecation and mydriasis are common in dogs with generalized-onset tonic-clonic seizures although not a constant feature. The ictus usually lasts 1 to 2 min. The post-ictal phase duration and clinical manifestations are variable. The dog may rest and rapidly return to normal activity or may show confusion, 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, which can persist for 24 h or longer. The post-ictal phase duration and severity of clinical manifestations may be unrelated to the duration and severity of the ictus.
Table 3.2. Seizure classification based on clinical manifestations.
| Generalized-onset seizures | Tonic-clonic |
| Tonic | |
| Clonic | |
| Myoclonic | |
| Atonic | |
| Absence | |
| Focal-onset |