|
|
| (14 intermediate revisions by 8 users not shown) |
| Line 1: |
Line 1: |
| − | ==Introduction==
| + | {{toplink |
| − | | + | |backcolour = E0EEEE |
| − | * '''Seizures''' are paroxysmal changes in cerebral cortex electrical activity that start abruptly, end suddenly and have a tendency to recur.
| + | |linkpage = Nervous System - Pathology |
| − | * '''Epilepsy''' is the occurence of recurrent seizures.
| + | |linktext =Nervous System |
| − | | + | |maplink = Nervous System (Content Map) - Pathology |
| − | ==Pathophysiology== | + | |pagetype =Pathology |
| − | | |
| − | * Seizures occur when there is imbalance between exitatory and inhibitory processes. This may be due to :
| |
| − | ** Inadequate neuronal inhibition.
| |
| − | *** Major inhibitory neurotransmitters include GABA and glycine.
| |
| − | ** Excessive neuronal excitation.
| |
| − | *** Major excitatory neurotransmitters include aspartate and glutamate.
| |
| − | | |
| − | ===Proposed Mechanisms===
| |
| − | | |
| − | * Defective feed-forward inhibition or feed-back initiation of inhibitory neurons in cortical circuits.
| |
| − | ** Recurrent excitatory collaterals may be formed.
| |
| − | * Changes in membrane properties of neurons.
| |
| − | ** These may include changes at:
| |
| − | *** Potassium, sodium, chloride and calcium ion channels
| |
| − | *** GABA receptors
| |
| − | *** Nicotinic acetyl choline receptors
| |
| − | *** NMDA receptors
| |
| − | **** Activation.
| |
| − | * Changes in the ionic microenvironment.
| |
| − | | |
| − | ===Seizure Development===
| |
| − | | |
| − | # At the onset of a seizure, abnormal neurons undergo prolonged depolarisations.
| |
| − | #* These depolarisations are associated with the rapid firing of repeated action potentials.
| |
| − | # Depolarisation of abnormal neurons recruits adjacent neurons with which they are connected.
| |
| − | # The electrical discharges of the large number of neurons involved become linked together.
| |
| − | # A storm of electrical activity results, causing a clinical seizure.
| |
| − | # Seizures may then spread:
| |
| − | #* To adjacent areas of the brain.
| |
| − | #* Through established anatomic pathways to other distant areas.
| |
| − | | |
| − | ==Nomenclature==
| |
| − | | |
| − | * '''Status epilepticus''' is the term used to describe
| |
| − | ** A seizure lasting longer than 5 minutes, or
| |
| − | ** A collection of discrete seizures without full recovery of consciousness.
| |
| − | * '''Cluster seizures''' occur when 2 or more seizures are experienced in a brief periods, but the patient regains consciousness between them.
| |
| − | * Three classes of seizures are recognised:
| |
| − | *# Generalised seizures
| |
| − | *# Focal seizures
| |
| − | *# Focal generalising seizures
| |
| − | | |
| − | ===Generalised Seizures===
| |
| − | | |
| − | * Generalised seizures may be:
| |
| − | ** Idiopathic
| |
| − | ** Symptomatic
| |
| − | *** Due to intracranial disease e.g. neoplasia, storage diseases etc.
| |
| − | ** Cryptogenic
| |
| − | *** There is probably an underlying cause but it cannot be identified by the diagnostic tests available.
| |
| − | ** Reactive
| |
| − | *** Due to some extracranial disorder, for example a toxin or metabolic disorder.
| |
| − | | |
| − | ====Clinical Signs====
| |
| − | | |
| − | * Initial clinical signs show involvement of both cerebral hemispheres.
| |
| − | * Generalised seizures result in:
| |
| − | ** Change in consciousness
| |
| − | ** Motor activity
| |
| − | *** Tonic-clonic seizures are most common in dogs and cats.
| |
| − | ** Autonomic signs
| |
| − | * The body's energy utilisation can increase to around 250% of the normal value during a generalised seizure.
| |
| − | | |
| − | ====Stages====
| |
| − | | |
| − | # Prodromal Phase
| |
| − | #* The animal experiences an indication of a forthcoming seizure.
| |
| − | #* This occurs hours to days before the event itself.
| |
| − | # Aural Phase
| |
| − | #* This is the very start of the seizure.
| |
| − | #* Behaviour changes may be apparent.
| |
| − | # Ictal Phase
| |
| − | #* The seizure "proper".
| |
| − | # Postictal phase
| |
| − | #* Consists of transient neurological and behavious changes, which can last from hours to days.
| |
| − | | |
| − | ====[[Idiopathic Epilepsy]]====
| |
| − | | |
| − | ====Acquired Generalisd Seizures====
| |
| − | | |
| − | * Other general seizures may be acquired.
| |
| − | * Seizures can occur at any age, but generally occur in animals younger than 2 years and older than 5 years.
| |
| − | * Causes may include:
| |
| − | ** Intracranial disease
| |
| − | *** Neoplasia
| |
| − | *** Trauma
| |
| − | *** Infection
| |
| − | *** Inflammation
| |
| − | ** Extracranial disease (also known as "reactive epilpsy").
| |
| − | *** Electolyte disorders
| |
| − | *** Metabolic disorders
| |
| − | *** Toxicity
| |
| − | | |
| − | ===Focal Seizures===
| |
| − | | |
| − | * Almost always an acquired disease.
| |
| − | * Active diseases often progress to become more general.
| |
| − | ** Cause generalised seizures.
| |
| − | | |
| − | ===Simple Focal Seizures===
| |
| − | | |
| − | * Onset occurs in a limited area of one cerebral hemisphere.
| |
| − | * No impairment of consciousness.
| |
| − | | |
| − | === Complex Focal Seizures===
| |
| − | | |
| − | * Arise in a single brain region, but cause impaired consciousness.
| |
| − | | |
| − | ==Causes of Acquired Seizures==
| |
| − | | |
| − | {| border="3" cellpadding="8"
| |
| − | !width="150"|'''<u>Cause</u>'''
| |
| − | !width="400"|'''<u>Examples</u>'''
| |
| − | | |
| − | |-
| |
| − | |Neoplasia
| |
| − | |Primary or metastatic
| |
| − | |-
| |
| − | |Inflammatory
| |
| − | |Distemper, FIP, FeLV/FIV, rabies, cryptococcosis (cats), toxoplasmosis
| |
| − | |-
| |
| − | |Traumatic | |
| − | |Immediate or delayed
| |
| − | |-
| |
| − | |Vascular
| |
| − | |Feline ischaemic encephalopathy, thromboembolism, hypertenstion
| |
| − | |-
| |
| − | |Anomalous
| |
| − | |Hydrocephalus
| |
| − | |-
| |
| − | |Metabolic
| |
| − | |Hepatic encephalopathy, uraemia, hyperparathyroidism, hypolycaemia, hyperkalaemia, hypocalcaemia, hypoxia, acid-base disorders, hyperthermia
| |
| − | |-
| |
| − | |Toxic
| |
| − | |Lead, organophosphates, metaldehyde, strychnine
| |
| − | |}
| |
| − | [[File:Causes of Epilepsy in cats and dogs older than 6 years.pdf|alt=|thumb|Causes of Seizures in Cats and Dogs older than 6 Years]]
| |
| − | | |
| − | ==Investigation of Seizures==
| |
| − | | |
| − | * It must first be determined whether seizure activity is in fact a seizure, rather than a non-epileptic paroxysmal event, for example:
| |
| − | ** Syncope
| |
| − | ** Exercise-induced weakness
| |
| − | ** Obsessive-compulsive behaviour
| |
| − | ** Narcolepsy
| |
| − | * Idiopathic epilepsy may be differentiated from secondary or reactive seizures by considering:
| |
| − | ** Age of onset
| |
| − | ** Breed disposition
| |
| − | ** Partial seizures or asymmetrical post-ictal signs
| |
| − | *** These suggest a discrete lesion.
| |
| − | ** Older animals (>5 years) may be more likely to have an acquired aetiology.
| |
| − | ** Younger animals (<6 months) may be more likely to have toxic or metabolic causes.
| |
| − | * Useful tests include:
| |
| − | ** Metabolic screening
| |
| − | ** Haematology
| |
| − | ** Serum biochemistry
| |
| − | ** Urinalysis
| |
| − | ** Serology.
| |
| − | ** Bile acid stimulation test
| |
| − | ** Serum lead
| |
| − | ** MRI and CT scanning, and CSF analysis, help rule out cancer.
| |
| − | <br><br>
| |
| − | | |
| − | {{Template:Learning
| |
| − | |podcasts = [[Seizures podcast|RVC clinical podcast about seizures]]<br>
| |
| | }} | | }} |
| − | | + | <br> |
| − | [[Category:Central Nervous System - Pathology]]
| |
