Canine and Feline Epilepsy. Luisa De Risio
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seizures
Tonic-clonic seizures also have been reported as the most common type of generalized-onset seizures in cats (Schwartz-Porsche and Kaiser, 1989; Schriefl et al., 2008). During the pre-ictal phase cats may display aggressiveness (hissing and growling), vocalization (including growling and crying), restlessness (running around erratically), anxiety, hiding or increased affection (seeking refuge with the owner), or may act as fearful. The clinical manifestations of the ictus can be violent and sometimes result in self-inflicted trauma such as excoriations, contusions, avulsion of nails and biting of the tongue (Schwartz-Porsche and Kaiser, 1989; Quesnel et al., 1997). Cats may be propelled forward, up in the air and from side to side. Facial muscle twitching is often observed before or after the tonic phase of the seizure. Autonomic manifestations such as mydriasis, salivation, piloerection and urination and occasionally defecation can also occur (Quesnel et al., 1997). The ictal phase usually lasts 30 s to 2 min. The post-ictal phase is similar to dogs, lasting minutes to several hours or days and is characterized by restlessness, disorientation, aimless wandering, thirst and hunger. Both cats and dogs may sleep for a few hours after the termination of the seizure.
GENERALIZED-ONSET TONIC SEIZURES. Tonic seizures are characterized by sustained increase in muscle contraction without clonic motor activity. Impairment of consciousness and autonomic manifestations can occur. The pre- and post-ictal phases are similar to those described for generalized-onset tonic-clonic seizure.
GENERALIZED-ONSET CLONIC SEIZURES. Clonic seizures are characterized by regularly repetitive, sudden, brief, involuntary contractions, which involve the same muscle groups, and are prolonged. Impairment of consciousness and autonomic manifestations can occur. The pre- and post-ictal phases are similar to those described for generalized-onset tonic-clonic seizure.
Tonic or clonic seizures alone have been reported uncommonly in dogs and cats (Schwartz-Porsche and Kaiser, 1989; Heynold et al., 1997; Licht et al., 2002, 2007).
GENERALIZED-ONSET MYOCLONIC SEIZURES. Myoclonic seizures are characterized by sudden, brief, involuntary, shock-like contractions that can be generalized or confined to individual muscles or muscle groups (e.g. face, trunk, one extremity).
This type of seizure has been reported in the miniature wire-haired dachshund, beagle and basset hound dogs in association with Lafora disease (Jian et al., 1990; Fitzmaurice et al., 2001; Gredal et al., 2003). The clinical presentation is characterized by repetitive, brief myoclonic jerking of the head, neck and thoracic limbs that are frequently strong enough to cause the animal to fall backward into a sitting or lying position (Davis et al., 1990; Fitzmaurice et al., 2001; Schoeman et al., 2002). Myoclonic seizures may occur spontaneously or in response to visual (including light), tactile or auditory stimuli (Fitzmaurice et al., 2001; Webb et al., 2009). Myoclonic seizures have been reported also in cats (Schwartz-Porsche, 1989). Not all myoclonic jerks are seizures, as they can result from other causes.
GENERALIZED-ONSET ATONIC SEIZURES. Atonic seizures are characterized by sudden loss of postural tone of the head, one limb, or of the entire body usually lasting 1, 2 or more seconds. Consciousness may be lost. This type of seizure has been reported in dogs (Podell, 2004) and needs to be differentiated from narcolepsy/cataplexy and syncope (see Table 9.1, Chapter 9). Generalized seizures characterized by collapse, loss of consciousness and minimal limb movements have been reported in a cat with structural epilepsy (Barnes et al., 2004) and may represent a form of atonic seizure activity.
GENERALIZED-ONSET ABSENCE SEIZURES. Absence seizures (formerly called petit mal seizures) are characterized by a transient and brief impairment of consciousness associated with a characteristic EEG pattern (2.5- to 4-Hz spike-and-wave complexes) (see Fig. 11.12, Chapter 11). Absence seizures have been clinically described as a transient cessation of activity with staring, unresponsiveness and ‘blanking out’ episodes. Absence seizures with myoclonic features have been reported in an 8-month-old male Chihuahua that presented with recurrent episodes of head and nose twitching associated with intermittent hind-limb jerking and suspected staring for a few seconds (Poma et al., 2010). Video-EEG documented multiple staring episodes either alone or in association with head and/or nose myoclonic jerks associated with generalized bilaterally synchronous 4 Hz spike-and-wave complexes (Poma et al., 2010). Absence seizures may occur also in cats, but they have not been reported as such or supported by EEG findings. One feline study reported a ‘mild’ form of generalized seizure activity characterized by transient cessation of activity, impaired consciousness, and bilateral facial muscle twitching for a few to several seconds (Quesnel et al., 1997). These may have been a form of absence seizures in cats. Unless absence seizures are frequent, associated with some motor manifestations or the pet-owner is very observant, they go unrecognized. Video-EEG monitoring is very helpful in the diagnosis of this type of seizure.
Focal-onset seizures
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