302 Pathophysiology of seizures Flashcards
How do seizures spread?
Simple partial seizures
-local cortical spread
Complex partial seizures
-usually bilateral via white matter commissures
Secondary generalized seizures
-via thalamus
What are primary generalised seizures?
-Tonic-clonic
-Myoclonic, brief muscle jerks, typically UL
-Absence, loss awareness usually < 30 secs
immediate recovery
What does tonic-clonic mean?
Involves both tonic (stiffening) and clonic (twitching or jerking) phases of muscle activity
What does semiology mean?
The study of signs
Eg. symptoms that act as signs to show where in the brain the seizure is happening
What is the semiology of a frontal lobe partial seizure?
-Often nocturnal
-Asymmetric fencing posture (SMA)
-Hyper-motor seizures (ventral)
-Cycling movements of legs, alternating limb movements, right-to-left head rolling, or agitated behaviour
What is the semiology of a primary visual cortex partial seizure?
-Simple visual hallucinations
Eg. flashing blobs or shapes
-One visual hemifield
-Post-ictal amaurosis
What is amaurosis?
A temporary loss of vision in one or both eyes due to a lack of blood flow to the retina
What is the semiology of a medial temporal partial seizure?
-Olfactory hallucinations
-Deja vu
-Epigastric rising “butterflies”
-Chewing, lip smacking, swallowing
What is the semiology of a lateral temporal partial seizure?
-Auditory hallucinations
-Language disturbances - dominant hemisphere
-Vestibular hallucinations
-Complex visual hallucination - imagery, scenes
What is the semiology of a insular cortex partial seizure?
-Gustatory halluination - often unpleasant
Choking feeling
-Peri-oral parasthesia
-Pain
-Hyperventilation
-Tachycardia
-Vomiting
-Hyper-motor
-Automatisms
What is the semiology of a primary somatosensory cortex partial seizure?
Tingling
What are automatisms?
Involuntary, non-purposeful, stereotyped, and repetitive behaviours
Usually occur in association with impaired awareness:
-Concussion
-Syncope
-Complex partial seizures
Pathophysiology:
-Release phenomena (disinhibition)
-Central pattern generator (excitation)
What is juvenile myoclonic epilepsy?
Most common primary generalized epilepsy
Onset 8-30 years (mean 14 years)
-Myoclonic, absence and generalized tonic clonic seizures
Excellent response to valproate ± clonazepam
What is temporal lobe epilepsy?
Epilepsy that starts in the temporal lobe area of your brain
-Slow waves in fronto-parietal networks & DMN
-Thalamic involvement
-Bilateral temporal lobe involvement
-Left hemisphere involvement
?Spread of seizure activity to “pools” of inhibitory subcortical GABA neurones
?Inhibition of subcortical arousal systems in the upper brainstem, thalamus, hypothalamus and basal forebrain
What is the pathophysiology of seizures?
Initiation
-Abnormal balance of excitatory vs inhibitory neuronal processes (esp glutamate vs GABA), leading to hyper-synchronization of pyramidal neurone firing
Propagation
-Feed forward and backward excitation
-Inactivation of inhibitory chloride channels
Termination
-Active process involving synchronous slow wave activity, on-off synchrony breaks the circuit
-Adenosine (purine) accumulation - also involved in sleep pressure
-Inhibitory neurotransmitters
-Endogenous opiates peptides
What are the different causes of seizures?
Idiopathic
Alcohol
Tumour
Post traumatic
Cardiovascular disease
What are Monogenic Epilepsies?
Related to genes that encode voltage-gated ion channels, including sodium, potassium, and chloride channels
What is hippocampal sclerosis?
The commonest cause of drug-resistant epilepsy in adults
The hippocampus is vulnerable to damage from seizure activity
40% of patients with HS have a history of Febrile Convulsions
What are Febrile Convulsions?
A seizure that can happen when a child has a fever
What factors can cause seizure development?
-Gliosis
-Inflammation
-Impairment of blood–brain barrier
-Neuronal changes
-Re-organization of the extracellular matrix (ECM)
What can cause gliosis?
Head injury
Stroke
How does gliosis cause seizures?
It can impair glial control of extracellular potassium ions and lead to excessively excitable neuronal border regions
What can cause provoked seizures?
It’s an acute response to brain insults
Eg. Brain trauma, stroke, encephalitis, meningitis, Fever, acute renal failure, hypoglycaemia, acute porphyria, electrolyte derangement
Drugs:
cocaine, OD of antidepressants
alcohol withdrawal, benzodiazepines or barbiturate withdrawal
What is important to include in a history of seizures?
-Time of day /night
Location & context
-Frequency
-Prodromal features
-Type of fall / collapse
-Triggers / common factors esp standing vs sitting
-Ictus description
-Witnessed account
-Duration of the episode (LOC, convulsion etc)
-Post-ictal features esp confusion, focal neurological symptoms
What are some examples of prodromal features of seizures?
-Visual darkening or tunnelling
-Light-headedness
-Vertigo
-Impending sense of loss of consciousness
-Sleepiness
-Heat, flushing
-Rapid onset
-Déjà vu, epigastric, rising sensations, piloerection, smells, tastes
-Focal neurological symptoms of any kind
Panic
What does prodromal mean?
The things that happen before the seizure episode
What is the significance of tongue biting during a seizure?
Tongue bit in the diagnosis of generalized tonic-clonic seizures
Sensitivity of 24%
Specificity of 99%
Specificity of lateral tongue biting of 100%
What is the significance of urinary incontinence during a seizure?
Urinary incontinence in the diagnosis of epileptic episodes
Systematic review 5 studies (221 epilepsy patients and 252 subjects with other episodes of LOC, including mainly syncope and functional episodes
Sensitivity 38%
Specificity 57%
Therefore, urinary incontinence has no value either in the differential diagnosis
What are some differentials for syncope?
-Reflex (vaso-vagal, cough, micturition, defecation)
-Othostatic
-Cardiogenic
-Seizures
-Hypoxia eg PE
-Hypoglycemia (diabetics on insulin and insulinoma)
-Vertebrobasilar TIAs
-Intoxication
-Cataplexy
-Drop attacks
-Psychogenic pseudo-syncope
Give example of double triple diagnosis’s of syncope
Panic -> hyperventilation -> syncope (due to cerebral vaso-constriction)
Panic -> hyperventilation -> migraine
Panic -> hyperventilation -> seizure (if susceptible)
Vertigo -> vomiting -> syncope
TLE -> arrythmia -> syncope
Syncope -> head injury > tongue bite, prolonged LOC & amnesia
Syncope in the elderly -> sleep
Syncope in the elderly -> TIA
What are functional seizures?
AKA psychogenic nonepileptic seizures (PNES) or dissociative seizures (DS)
Characterized by paroxysmal events that semiologically may look like epileptic seizures, but are not due to an underlying epileptic activity
