Neurological emergencies (Proceedings)

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Neurological emergencies (Proceedings)

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Aug 01, 2009


Seizures
Neurological emergencies are common in small animal practice. As with other body systems, infections, neoplasms, trauma, inflammatory processes, congenital and hereditary diseases all affect the central and peripheral nervous systems causing a range of mild to severe conditions. Advanced forms of imaging provided by computed tomography (CT) and magnetic resonance imaging (MRI) in veterinary medicine are allowing improved diagnostic plans and management options. The assessment, stabilization and treatment of the neurology emergency, however, still relies on the ability of the emergency clinician to consider a complete history, perform a complete physical examination, and analyze test results readily available on an emergency basis.

Definition/overview

Seizures are the physical manifestation of an abnormal balance between excitatory and inhibitory tone in the central nervous system. Seizures are categorized as either generalized or partial. Generalized seizures include those that, in the past, have been referred to as convulsions, or grand mal seizures. Partial seizures are further classified as either simple partial or complex seizures. Partial seizures include seizure activity that is atypical. Both generalized and partial seizures represent a potentially life-threatening neurological emergency usually requiring treatment.

Etiology

The central nervous system relies on a balance of excitatory tone and inhibitory tone for normal function of neurons. Generally, excitatory tone is mediated by the neurotransmitter glutamate, and inhibitory tone is mediated by gaba aminobutyric acid (GABA). Depolarization of the cell membrane results with binding of glutamate to its receptors. Hyperpolarization of the cell membrane occurs when GABA binds to its receptors. Uncontrolled, perpetuated neuronal activity may derail normal mechanisms that act to prevent random excitation, resulting in seizures.

Pathophysiology and clinical signs

Seizures may occur with a wide variety of conditions. These conditions are grouped according to intracranial causes (structural epileptic seizures or SES), extracranial causes (reactive epileptic seizures or RES), and idiopathic epilepsy (primary epileptic seizures or PES). Although each of these categories should be considered with animals presenting with acute or recent onset of seizures, the age of the animal may suggest one group over another. Animals less than 1 year or older than 5 years of age are more commonly represented in the SES group. Recurrent SES typically occur within 2-4 weeks of the acute onset (first seizure). Dogs aged 1 to 5 years old are more likely to have PES, and recurrent seizures may not recur for greater than 4-6 weeks. Cats develop PES very uncommonly without a prior inciting cause (eg, trauma or inflammation).

A cluster of seizures is a series of isolated seizures lasting over minutes to days. Status epilepticus is prolonged single seizure lasting more than 3 minutes without recovery. Status epilepticus can be life threatening, resulting in brain anoxia and residual brain impairment or death.

Categories of seizures
1. Generalized: loss of consciousness, tonic, clonic or myoclonic activity
2. Partial: unilateral, stereotypical or bizarre behavior
a. simple partial: no loss of consciousness
b. complex partial: altered mentation or loss of consciousness