Читать книгу Canine and Feline Epilepsy - Luisa De Risio - Страница 66

The clinical manifestations of focal-onset seizures (formerly called partial seizures) indicate initial abnormal neuronal activity localized in a particular area of a cerebral hemisphere (seizure focus). The newly proposed ILAE classification (Berg et al., 2010) introduces the concept of the seizure focus being discretely localized or more widely distributed within the affected hemisphere.

The clinical manifestations can vary considerably depending on the function of the affected cerebral area and include involuntary motor activity, autonomic signs, sensory abnormalities, alterations of consciousness and paroxysms of abnormal behaviour. These clinical manifestations may occur alone or in various combinations.

FOCAL-ONSET MOTOR SEIZURES. Focal-onset motor seizures are characterized by involuntary, generally unilateral motor activity resulting in abnormal movements of a body part, such as turning the head to one side, flexion and/or extension of one limb, contraction of facial or masticatory muscles. Focal-onset motor seizures are presumed to arise from a seizure focus near a primary motor area in the frontal cortex contralateral to the observed involuntary motor activity.

FOCAL-ONSET AUTONOMIC SEIZURES. Focal-onset autonomic seizures result in one or more autonomic manifestation including mydriasis, hypersalivation, piloerection, lacrimation, urination, defecation, vomiting, diarrhoea and apparent abdominal pain (Breitschwerdt et al., 1979; Licht et al., 2002; Berendt et al., 2004). Phenobarbitone-responsive hypersalivation, dysphagia, salivary gland enlargement and oesophageal spasms have been reported in a few dogs and may be a form of focal autonomic seizure (Stonehewer et al., 2000; Gibbon et al., 2004).

FOCAL-ONSET SENSORY SEIZURES. Focal-onset sensory seizures result in abnormal sensations such as paraesthesia (numbness, tingling) limited to a defined somatosensory region of the body, or in visual hallucinations. Sensory seizures have been subclassified into somatosensory and special sensory (visual, auditory, olfactory, gustatory and vestibular) in humans (Commission, 1981). It is likely that the same sensory disturbances occur in animals, but they are difficult or impossible to identify and associate with concurrent EEG abnormalities. Therefore it can only be speculated that episodes characterized by chewing and/or licking into the air or at a specific region of the body, rubbing of the face, or biting at imaginary objects (‘fly biting’ or ‘fly catching’) are the manifestation of sensory seizures. Repetitive episodes of ‘fly biting’ could be the consequence of focal sensory seizures in the visual cortex, similar to focal visual sensory seizures that occur in humans (Cash and Blauch, 1979; Licht et al., 2002), could result from focal seizures with paroxysms of abnormal behaviour (Berendt et al., 2004), or may represent a form of compulsive behavioural disorder (see Chapter 9) (Rusbridge, 2005).

In analogy with the human classification published by the ILAE in 1981 and the veterinary medical literature, focal seizures have been referred to as complex and simple depending on whether or not consciousness is altered. However, in the context of the ILAE classification, consciousness was defined as ‘the degree of awareness and/or responsiveness of the patient to externally applied stimuli’. Responsiveness was defined as ‘the ability of the patient to carry out simple commands or willed movement’ and awareness referred ‘to the patient’s contact with events during the period in question and its recall’. These functions are difficult if not impossible to assess in veterinary patients, especially based on the pet-owner description or video documentation (Berendt et al., 2004). Therefore veterinary medicine can follow the most recent recommendation of the ILAE (Berg et al., 2010) to avoid using ictal impairment of consciousness to classify specific seizure types (e.g. simple and complex focal seizures) and to describe individual seizure phenomenology accurately including impairment of consciousness/awareness, when recognized.

Focal seizures can also occur as stereotyped paroxysms of abnormal behaviour including attention-seeking or avoidance/escaping behaviour, aimless wandering, restlessness and unprovoked aggression (Licht et al., 2002; Berendt et al., 2004). Paroxysmal abnormal behaviour may result from a manifestation of sensory seizures, involvement of the limbic system or higher cerebral activity (psychic seizures according to the 1981 ILAE classification). Episodes characterized by impaired consciousness (‘trance-like staring’), abnormal behaviour, including unprovoked aggression, extreme irrational fear, compulsive tail-chasing and fly catching, have been reported as focal seizures in eight bull terriers with interictal EEG abnormalities (multiple epileptiform spikes) and moderate to severe ventriculomegaly on computed tomography (Dodman et al., 1996).

The terms complex partial (or focal) seizures, psychomotor seizures, temporal lobe and limbic seizures or epilepsy have been used interchangeably in the veterinary literature to indicate focal seizures characterized by paroxysms of abnormal behaviour with or without some degree of impairment of consciousness.

Any type of focal-onset seizure can evolve into a generalized seizure (secondarily generalize).

The onset of ictus is characterized by clinical (usually motor) manifestations consistent with the location of the seizure focus and within seconds to minutes seizure activity spreads to involve both cerebral hemispheres resulting in bilaterally symmetrical motor disturbances (usually tonic-clonic), autonomic dysfunction and (commonly) altered consciousness. The focal onset may be subtle and the secondary generalization can occur so rapidly that the initial focal component is undetected and the seizure is misclassified as a generalized-onset seizure. Close observation is essential to recognize the focal-onset of the seizure before its secondary generalization. If the terminology recently proposed by the ILAE (Berg et al., 2010) is embraced also in veterinary medicine, the term ‘secondarily generalized’ should be abandoned and replaced by a description of localization and progression of ictal events.

Focal-onset seizures have also been reported in cats (Quesnel et al., 1997; Barnes et al., 2004; Schriefl et al., 2008; Pákozdy et al., 2010). As in dogs, clinical manifestations include motor, sensory and autonomic signs, alterations of consciousness, and paroxysms of abnormal behaviour, which can occur alone or in various combinations. Reported clinical manifestations include lack of response to sensory stimuli, unilateral facial twitching (that can be limited to the ear, lip, or eyelids), turning the head to one side, repetitive movements of one or both limbs on one side of the body, mydriasis, hypersalivation, urination, abnormal behaviour suggestive of some form of hallucinations (unjustified hissing, growling, piloerection, attacking a real or imaginary object, unprovoked startle, running frantically, often blindly, into objects), self-chewing, biting and circling (Schwartz-Porsche and Kaiser, 1989; Quesnel et al., 1997). As in dogs, focal seizures have been reported to secondarily generalize in cats (Quesnel et al., 1997; Schriefl et al., 2008).

A peculiar type of feline focal seizures characterized by orofacial involvement, impaired consciousness, occurrence in clusters and frequent association with hippocampal pathology has been described (Pákozdy et al., 2011). Ictal signs include hypersalivation, facial twitching, lip smacking, chewing, licking, swallowing, mydriasis, motionless staring and vocalization. Secondary generalization occurs in the majority (12/15, 70%) of cats. The most common post-ictal and interictal signs are behavioural changes and aggression. Antibodies against voltage-gated potassium channel complexes may play a role in the pathogenesis of this type of feline focal seizure (Pakozdy et al., 2013).

In addition to a classification based on clinical manifestations, seizures have also been classified based on underlying aetiology (Table 3.3). The aetiology-based classification allows for a more specific differential diagnosis. Reported aetiologies of reactive and structural seizures in dogs and cats are described in detail in Chapters 4 and 5, respectively. Idiopathic epilepsy is presented in Chapter 6.