Seizures

24 Seizures


Seizure disorders represent a relatively common reason for emergency consultation and presentation. Seizures are classified as generalized or partial/focal, and the tonic–clonic form of generalized seizures forms the basis of the following discussion. In some animals with generalized seizures, the inciting cause is transient or rapidly reversible (e.g. intoxication, hypoglycaemia), while in others seizures occur due to a more long-term abnormality (e.g. chronic brain disorder resulting in epilepsy). The causes of seizures are typically divided into primary intracranial or extracranial causes and are summarized in Box 24.1.



BOX 24.1 Causes of seizures




Primary intracranial



• Idiopathic epilepsy (especially purebred and large dogs, first onset 1–5 years old)

• Intracranial neoplasia, primary or metastatic (especially older animals)

• Noninfectious inflammatory central nervous system (CNS) disease

• Infectious causes

• Cerebrovascular abnormalities

• Developmental abnormalities, especially younger animals (e.g. hydrocephalus)

• Degenerative disorders (e.g. storage diseases)

• Traumatic brain injury

• Intracranial haemorrhage (e.g. due to systemic hypertension, coagulopathy)


Extracranial



• Hypoglycaemia

• Intoxication (e.g. metaldehyde)

• Hepatic encephalopathy (e.g. portosystemic shunt)

• Hyper- or hyponatraemia

• Hypocalcaemia

• (Uraemic encephalopathy – rare cause of seizures)


Nursing Aspect


Owners quite commonly ring for advice with respect to cats and especially dogs that have suffered one or more seizures and the duty nurse is often the person from whom this initial advice is obtained. In the author’s opinion, not all animals that have suffered a seizure need to be examined. The recommendation to examine the animal at the clinic should be guided by the owner’s wishes but also after obtaining adequate information with respect to:


• Current status with respect to postictal abnormalities and recovery

• Number of seizures and their timing

• Nature and duration of the seizure(s)

• Any known history of exposure to possible inciting factors (e.g. toxins, trauma)

• Previous seizure history

• Previous medical and therapeutic history.

In animals that have suffered only one self-limiting (isolated) seizure, that appear to have recovered satisfactorily, and in which an obvious inciting cause has not been identified, it may be appropriate for the animal to remain at home for close monitoring. However, owners must be advised to ensure that the animal is not able to harm him/herself should another seizure occur. They should also contact the practice again either if another seizure occurs or if behavioural signs suggestive of prodrome or aura (pre-seizure behaviour) are observed.


It is recommended that animals with cluster seizures (two or more seizures within 24 hours) are examined as soon as possible, and animals in status epilepticus must be presented to the clinic immediately.



Approach to Seizures



Signalment


Signalment is important when considering the possible aetiology of a seizure disorder. For example, young animals are more likely to suffer intoxication from dietary indiscretion or to seizure as a result of congenital anomalies. Hypoglycaemia-induced seizures are more common in puppies, especially of toy breeds, while older animals are more likely to seizure as a result of intracranial neoplasia. Idiopathic epilepsy is more common in certain breeds (e.g. German shepherd dogs) and affected animals usually seizure for the first time at 1–5 years of age. Intracranial tumours are more common in certain breeds (e.g. Boxers), as are the range of inflammatory central nervous system diseases (e.g. Maltese terriers, Yorkshire terriers, Pugs). True idiopathic epilepsy is much less common in cats than it is in dogs.



History




Clinical Tip



• It is important to remember that owners may mistake other episodes of abnormal behaviour for seizures and this distinction may be crucial in some cases. In particular, animals suffering from syncope of cardiac origin may temporarily lose consciousness and demonstrate involuntary urination while recumbent. However, these animals typically return to complete normality within seconds to a minute of the onset of the episode and this provides a useful distinguishing feature from the postictal period associated with seizures. Severe acute vestibular signs may also be mistaken for seizures (see Ch. 15).

A thorough history is mandatory for all animals with seizures, although the timing should be governed by the patient’s clinical status on presentation. Owners should be asked to describe the seizure episode(s) as thoroughly as possible, including pre-, intra- and postictal phases. It is important to establish the number of seizures that have occurred and their timing, the nature and duration of the seizure(s), any known or possible exposure to inciting factors (e.g. intoxication; recent feeding with portosystemic shunt), previous seizure history and previous medical history. If the patient is already on anticonvulsive therapy, the drugs, dosages and timing of last administration should be established. Details of any monitoring of serum anticonvulsant levels should be obtained if the owner knows this information.



Major body system examination


Major body system examination may need to be delayed in an animal that presents actively seizuring. Neurological examination may be normal or severely abnormal in animals with seizure disorders. Some animals present in the middle of a seizure, some with postictal abnormalities, while others have fully recovered. A full neurological examination is warranted in any animal with a seizure history but it is sometimes necessary to wait for postictal abnormalities to resolve before a reliable examination can be performed. In addition, anticonvulsive medications that may need to be administered in an emergency will also potentially alter the findings of a neurological examination.


Cardiovascular examination may be abnormal in animals that have seizured. True seizures are unlikely to occur as a result of a primary cardiovascular disorder although cerebrovascular abnormalities may cause other neurological signs. Cardiovascular abnormalities that may occur secondary to seizures include tachycardia, hyperaemic mucous membranes and rapid capillary refill time. Furthermore, in some cases the cause of the seizure may also have direct effects on the cardiovascular system; this is especially common with certain poisons. In general, seizures should not cause systemic hypoperfusion but perfusion abnormalities may be seen following severe sustained seizure activity. In addition, the author has anecdotally noted a variety of cardiovascular abnormalities in animals with primary brain disease that have been presumed to be a direct result of the cerebral disorder (a brain–heart connection has been documented in people). Finally, depending on the cause of the seizures and their severity and duration, some animals may present with intracranial hypertension that may be detectable clinically as bradycardia and systemic hypertension (Cushing’s reflex – see Ch. 28). If facilities allow, systemic blood pressure should be measured in all animals presenting with active seizures or marked postictal abnormalities.


Respiratory examination may or may not be normal in animals with seizures. Seizures are unlikely to occur as a result of a primary respiratory disorder and the most common respiratory abnormalities identified are panting and tachypnoea. Aspiration may occur as a consequence of seizuring and other abnormal respiratory findings are possible in such cases. Neurogenic (noncardiogenic) pulmonary oedema may also cause respiratory abnormalities.


Rectal temperature may be normal, decreased or increased in animals with seizures depending on the timing of presentation. Severe seizure activity, in particular status epilepticus (see below), may result in marked hyperthermia which may need to be managed specifically (see Ch. 16).

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Sep 3, 2016 | Posted by in SMALL ANIMAL | Comments Off on Seizures

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