USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 3-year-old boy comes to the emergency department because of a convulsion. This has never occurred before. The child has had an upper respiratory infection for the past two days. Family history is significant for febrile seizures in his father. On physical examination, the patient’s temperature is 38.5°C (103.1°F). He appears tired but is cooperative. His pharynx is erythematous. Neurological examination reveals no abnormalities. Which of the following is the most appropriate treatment of this condition?
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.
- "Robbins Basic Pathology" Elsevier (2017)
- "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
- "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)