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Febrile seizure

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Nervous system

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Febrile seizure

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Febrile seizure

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A 2-year-old boy is brought to the emergency department by his parents after he fell to the ground and started shaking uncontrollably. According to his parents, while the boy was playing, his body suddenly stiffened, and he fell to the ground and started shaking. The episode lasted approximately one minute, after which the patient briefly lost consciousness. The parents state he regained consciousness within a minute but seemed confused and disoriented. The patient has been experiencing a fever, sore throat and runny nose for the past two days. The symptoms were improving with acetaminophen until today, when he developed high-grade fever and chills. Medical history is noncontributory, and the patient has been achieving developmental milestones appropriately. The patient’s temperature is 39.4°C (103°F), pulse is 140/min, respirations are 30/min, and blood pressure is 92/55 mm Hg. The child is comfortably playing with a toy and does not appear to be in distress. Physical examination shows an erythematous pharynx without exudate or vesicles. There is no nuchal rigidity or photophobia. Which of the following is the most likely diagnosis?  

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Transcript

Febrile seizures are seizures that happen with a fever, and they typically occur in young children between six months and five years of age.

Now, neurons are the main cells of the nervous system. They’re composed of a cell body, which has all the cell’s organelles, and nerve fibers, which are projections that extend out from the neuron cell body.

Nerve fibers are either dendrites that receive signals from other neurons, or axons that send signals signals called action potentials along to other neurons.

Where two neurons come together is called a synapse, and that’s where one end of an axon sends neurotransmitters to the dendrites or directly to the cell body of the next neuron in the series.

Some neurotransmitters bind to the receptors and tell the cell to open up the ion channels and relay an electrical message and these are called excitatory neurotransmitters.

But there are others which can close the ion channels and prevent an electrical message from going through and these are called inhibitory neurotransmitters.

The main excitatory neurotransmitter in the brain is glutamate.

Glutamate binds to NMDA receptors which tell the cell to open up calcium ions channels. Since calcium has a positive charge, it makes the inside of the cell more positive and that helps triggers an action potential.

On the flip side, the main inhibitory neurotransmitter in the brain is GABA.

GABA binds to GABA receptors, which tell the cell to open up chloride ion channels.

Since chloride has a negative charge, it makes the inside of a cell more negative and that inhibits an action potential.

During a seizure, large groups of neurons become active synchronously, meaning all at the same time.

And in a febrile seizure, the trigger for that neuronal activity is a fever.

So that makes you wonder, why? Well, we actually don't know for sure, but there are some possible explanations. The first is that a fever, raises the core body temperature and it makes neurons more excitable than usual - meaning that action potentials are more likely to happen.

The second is that fever causes hyperventilation, which is when you breathe faster and have a decreased level of carbon dioxide in the blood. That leads to a respiratory alkalosis, or an increase in blood pH, which also seems to make neurons more excitable.

The third is that fevers are caused by cytokines like interleukin-1β, that get released by white blood cells during the body’s innate immune response.Cytokines are thought to also enhances the activity of the NMDA receptors.

Of course, most of the time, people have fevers without having seizures, so these factors are just part of the story.

While we don't know for sure what causes febrile seizures we do know there are certain risk factors.

Genetics seems to play a role as children whose parents had febrile seizures are more likely to also have them.

Age seems to also be a factor, because although febrile seizures happen in children between the age of 6 month to 5 years, the majority happen in children that are 12 to 18 months of age.

Summary

Febrile seizures are a type of seizure that can occur in children with fever (>38℃). A seizure is a sudden, uncontrolled electrical disturbance in the brain. Febrile seizures typically affect children from 6 months to 5 years old, who do not have epilepsy or any other defined cause of seizures.

Febrile seizures usually occur in about 2%–4% of children younger than 5 years of age. Boys are more likely than girls to have febrile seizures, and there is a risk for recurrence if a child has had one before. Even though most febrile seizures are self-limiting and last for just a few seconds to minutes, some can last for up to 30 minutes, and antiseizure medications are recommended for those that continue for more than 5 minutes.

Sources
  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "Fever, febrile seizures and epilepsy" Trends in Neurosciences (2007)
  6. "Brain Inflammation in Epilepsy: Experimental and Clinical Evidence" Epilepsia (2005)
  7. "The Blood?Brain Barrier and Epilepsy" Epilepsia (2006)