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June 14, 2023 | by Catrina Hacker, PennNeuroKnow and IAES Collaboration
A message from IAES Blog Staff:
The staff at IAES is proud to present to all of you another wonderful article/blog from the amazing team at PennNeuroKnow. Since 2019 IAES has been extremely lucky to be in partnership with the PennNeuroKnow(PNK) team to help us all better understand complex medical issues related to AE and neurology in general. The talented PNK team continues to keep us up-to-date and help clarify the complexities we face each day along our AE journey, and we are eternally grateful! You can find out much more about this stellar group at: https://pennneuroknow.com/
——-
There are many subtypes of autoimmune encephalitis (AE) that vary in their causes, the symptoms that patients experience, and what treatments are most effective. One of several factors that distinguish these different subtypes of AE is whether they involve intracellular or extracellular antibodies. In this post we will explore exactly what these terms mean and how they contribute to the differences between types of AE.
N Engl J Med 2018;378:840-51. DOI: 10.1056/NEJMra1708712 Copyright © 2018 Massachusetts Medical Society
When a virus or bacteria enters our body, our immune system mounts an attack to destroy the foreign invader and protect us from harm. If our immune system is like an army ready for battle, then antibodies are like the scouts sent ahead of the battalion, patrolling for signs of a threat. Just like security personnel might scan ID badges to determine who is allowed in a building, each antibody is tasked with looking for a particular feature of something that the body has deemed harmful, called an antigen1. You might have heard antibodies discussed in reference to COVID-19, where infection with COVID-19 or vaccination can cause your body to produce antibodies that recognize features of the COVID-19 virus2. When antibodies are already present in the body, they can recognize the newly-arrived COVID-19 virus and mount an attack more quickly, helping to avoid a more serious infection.
This ability to quickly mount a defense against a threat before getting too sick is what makes antibodies an important part of our body’s immune system army. However, antibodies are only helpful if they recognize and defend against foreign substances that are harmful. Unfortunately, this isn’t the case in AE. Patients with AE have antibodies that bind to proteins found in their own cells, called autoantibodies (the prefix “auto” means self, so autoantibodies are antibodies that bind the body’s own proteins)3. Autoantibodies trigger the body’s immune system to attack itself, leading to the many symptoms of AE.
Each antibody can recognize only a small part of a whole cell, and there are many different parts of a cell that an antibody can recognize. What distinguishes extracellular from intracellular antibodies is whether their antigen (the ID badge they’re looking for) is inside or outside of the cell1,4. Extracellular antibodies recognize antigens that are on the outer surface of the cell (“extra” meaning outside). Conversely, intracellular antibodies recognize antigens that are inside the cell (“intra” meaning inside). The intracellular antibodies inside the cell trigger a different set of immune reactions than the extracellular antibodies outside of the cell.
Subtypes of AE are distinguished by what kind of autoantibody a patient has4, which is why they are typically named after the antigen that the autoantibody recognizes. For example, patients with anti-NMDAR AE have antibodies that recognize NMDA receptors. Types of AE associated with antigens outside the cell involve extracellular antibodies and types of AE associated with antigens inside the cell involve intracellular antibodies.
Many of the most common subtypes of AE involve extracellular antibodies4,5. Most are associated with antibodies that recognize a kind of protein that sits on the surface of the cell called a receptor. Receptors recognize and bind specific molecules and send signals that tell the cell how to respond. The receptors on neurons, a type of brain cell, are especially important because one neuron communicates with another by releasing molecules that can be recognized by the other neuron’s receptors. When antibodies bind the receptors, they activate an immune response and disrupt the ability of those receptors to participate in neural signaling. This leads to the many neurological symptoms of AE. Subtypes with these kinds of antibodies include anti-NMDAR AE6, anti-AMPAR AE7, anti-mGLUR5 antibody encephalitis4,5, GlyR antibody encephalitis4, anti-GABAa AE8, and anti-GABAb AE9. Several other extracellular antibodies associated with AE have antigens that sit on the cell’s surface and help with neuronal signaling but aren’t receptors themselves. Subtypes of AE with these kinds of antibodies include LGI1-antibody encephalitis10, CASPR2-antibody encephalitis11, and DPPX-antibody encephalitis4,5.
Subtypes of AE associated with intracellular antibodies are less common4,5. One example is GAD-antibody encephalitis12. Patients with this form of AE have antibodies that target Glutamic Acid Decarboxylase (GAD), a protein found inside the cell that is needed to synthesize GABA, a special type of molecule that is necessary for some kinds of neural signaling. Other subtypes of AE that target intracellular proteins are anti-Hu encephalitis5, and Ma2-antibody encephalitis13.
One big distinction is that most subtypes of AE associated with intracellular antibodies are also associated with tumors4. These subtypes of AE are called paraneoplastic. Paraneoplastic AE can occur when tumor cells express proteins on their surface that are normally expressed elsewhere. Sometimes this includes proteins that are normally found inside healthy neurons. To recognize and fight the tumor, the body’s immune system creates antibodies that recognize these proteins. These antibodies don’t distinguish the proteins found in the tumor cells from the healthy proteins found in neurons, so when they reach the brain, they also bind the naturally-occurring proteins in neurons and trigger the immune response responsible for the symptoms of AE14.
Patients with subtypes of AE associated with intracellular antibodies also tend to have poorer outcomes and respond worse to immunotherapy than patients with subtypes associated with extracellular antibodies4,15. This is because many of the symptoms of AE associated with extracellular antibodies are thought to result from the antibodies disrupting the normal function of the cell-surface proteins that they target. Conversely, the presence of intracellular autoantibodies typically accompanies an immune response against neurons more broadly that results in neuronal death. This means that successful treatment can often reverse symptoms of AE resulting from extracellular antibodies, as limiting the action of the antibodies allows the neurons to function normally, whereas even after treatment, symptoms do not typically reverse in subtypes of AE associated with intracellular antibodies, as many neurons have already died. For patients with paraneoplastic AE, removing the tumor is also an important step toward relieving symptoms15.
Despite general differences in outcomes for subtypes of AE associated with extracellular and intracellular antibodies, early detection and treatment are key to successful outcomes for all subtypes of AE4. Determining which type of AE a patient has can have an important impact on how doctors choose to treat and manage the disease. This distinction is also important for researchers developing new treatments and possible cures, as approaches that might work for one type of AE may not work for others. Determining which patients will be most receptive to a particular new treatment leads to better outcomes for clinical trials, which means more treatment options for all patients.
References
On June 16 th, 2022, Tabitha Orth, President and Founder of International Autoimmune Encephalitis Society officially became the 7,315 th “point of light”. Recognized for the volunteer work she and IAES has done to spark change and improve the world for those touched by Autoimmune Encephalitis. The award was founded by President George H.W. Bush in 1990.
Become an Advocate by sharing your story. It may result in accurate diagnosis for someone suffering right now who is yet to be correctly identified. Submit your story with two photos to IAES@autoimmune-encephalitis.org
International Autoimmune Encephalitis Society (IAES), home of the AEWarrior®, is the only Family/Patient-centered organization that assists members from getting a diagnosis through to recovery and the many challenges experienced in their journey. Your donations are greatly appreciated and are the direct result of IAES’ ability to develop the first product in the world to address the needs of patients, Autoimmune Encephalitis Trivia Playing Cards. Every dollar raised allows us to raise awareness and personally help Patients, Families, and Caregivers through their Journey with AE to ensure that the best outcomes can be reached. Your contribution to our mission will help save lives and improve the quality of life for those impacted by AE.
March 8, 2023 | by Marissa Maroni, PennNeuroKnow and IAES Collaboration
A message from IAES Blog Staff:
The staff at IAES is proud to present to all of you another wonderful article/blog from the amazing team at PennNeuroKnow. Since 2019 IAES has been extremely lucky to be in partnership with the PennNeuroKnow(PNK) team to help us all better understand complex medical issues related to AE and neurology in general. The talented PNK team continues to keep us up-to-date and help clarify the complexities we face each day along our AE journey, and we are eternally grateful! You can find out much more about this stellar group at: https://pennneuroknow.com/
We all suffer from headaches from time to time. For some a headache is a daily medical issue and they can range from mild and slightly bothersome to migraines that put us in bed for a day or more at a time. This wonderful article by Marissa Maroni helps to shed light on the various types of headaches and the biology behind an issue that we all encounter!
We all suffer from headaches from time to time. For some a headache is a daily medical issue and they can range from mild and slightly bothersome to migraines that put us in bed for a day or more at a time. This wonderful article by Marissa Maroni helps to shed light on the various types of headaches and the biology behind an issue that we all encounter!
In the news or on your favorite medical drama you may have been startled to see patients are kept awake during brain surgery. If not, we’ve included an example here! Although it feels wild to witness awake surgeries, they’re possible because the brain itself cannot sense any pain. Despite the lack of pain sensed by the brain, most people do experience head pain at some point in their life, including headaches. The deep, throbbing pain, and sometimes nausea, experienced during a headache can be unbearable. But if brains can’t feel, what causes the pain of a headache and how is this treated?
There are three main types of primary headaches, primary meaning the headache is the issue, rather than a symptom from an underlying condition. The three types of primary headaches are:
Tension-type headaches are the most common primary headache and impact over 25% of people globally1. Tension-type headaches are characterized by mild to moderate head pain that feels like a tightening pressure (imagine hands gripped tightly around your head) that affects both sides of the brain, lasting minutes up to several days2.
Migraines effect approximately 14% of the global population1. Migraines are characterized as moderate to severe throbbing pain usually on one side of the brain with pain lasting from several hours to 3 days3. Migraines are usually accompanied by various symptoms such as nausea and light and sound sensitivity4.
Cluster headaches affect approximately 0.4% of people5. Cluster headaches are characterized by excruciating pain on one side of the brain usually surrounding the eye that lasts for minutes up to 3 hours5.
Each of the three primary types of headaches vary in their origin. Rather than extensively unpacking each, let’s focus in on migraines. Prior to a migraine starting a person can experience sound and light sensitivity, mood changes, thirst, and yawning among other symptoms. Scientists have used brain imaging prior to the start of migraines to try and understand why do they start in the first place and what could be causing pre-migraine symptoms?
It is theorized that the brainstem, the stalk of your brain that controls breathing and heart rate among other functions, is the generator of migraines6. A brain imaging study found activity in a subregion of the brainstem was associated with the time until the next migraine starts7. Further, a set of researchers from Germany imaged the brain of a migraine patient for 30 consecutive days to understand what events occur in the brain leading up to a migraine8. They found that before and during a migraine there is altered communication between the brainstem and the hypothalamus, a part of the brain important in controlling sleep, hunger, thirst, and more. Additionally, they found increasing activity in the hypothalamus in the time leading up to a migraine.
Scientists have identified critical brain regions that have altered brain activity prior to a migraine, but can any of this explain pre-migraine symptoms? Researchers hypothesize that the increased activity in the hypothalamus could explain pre-migraine symptoms such as yawning and thirst. Interestingly, migraine patients with light sensitivity have increased activation of the occipital cortex, a brain region responsible for vision perception, in comparison to migraine patients who did not experience light sensitivity9. Although the answer is not precise, scientists have identified altered brain signaling that may prime a brain for a migraine attack and identified specific brain regions that can explain pre-migraine symptoms.
A main piece to the migraine pain puzzle is a group of nerves that carry pain signals from the face to the brain, referred to as trigeminal ganglion. The trigeminal ganglion connect to the blood vessels surrounding your brain and various parts of the brain including the brainstem, hypothalamus, and thalamus (Figure 1). The thalamus is a place for information to be relayed to your cortex. The activation of trigeminal ganglion lead to a cascade of events that have roles in migraine pain. Let’s explore what events occur and how they contribute to migraine pain.
Figure 1. The trigeminal ganglion, in blue, makes connections to the brainstem, thalamus, and hypothalamus. The thalamus relays information to the cortex.
Sensitization of the brain
During a migraine, it is thought that the trigeminal ganglion become sensitized, meaning they can activate and send pain signals in response to nonpainful stimuli (Figure 2)3. Trigeminal ganglion sensitivity causes throbbing head pain, and pain felt when coughing or bending over during a migraine. Even though you are not doing anything to cause this pain, the trigeminal ganglion is sensitized and sending pain signals anyway! The sensitized trigeminal ganglion lead to the activation and sensitization of the brainstem, and thalamus10. Sensitization of the brainstem and thalamus contribute to allodynia, perception of pain by something not normally painful, like a gentle touch or glasses resting on your nose. Collectively, the sensitization of the trigeminal ganglion, brainstem, and thalamus play a critical role in migraine pain.
Figure 2. Three contributors to migraine pain: sensitization, hyperexcitability, and CGRP release.
Hyperexcitability
Hyperexcitability refers to neurons that are more likely to become active and send signals. General hyperexcitability is seen in individuals with migraines and is hypothesized to contribute to sensitization in the brain as there is more activation in pain signaling regions (Figure 2)3. Brain imaging studies identified that during a migraine the brain is hyper-responsive to sensory information3. This hyper-responsiveness is hypothesized to cause light sensitivity during migraines. Interestingly, when scientists examined shared mutations in the genes of migraine patients, they found that many of the mutated genes were important in neuronal signaling, further suggesting a role for hyperexcitability in migraines11.
Neuropeptide release
The activation of the trigeminal ganglion causes the release of neuropeptides. Neuropeptides are small proteins that cause changes in neuronal signaling (oxytocin is a well-known example of a neuropeptide). An important neuropeptide released after trigeminal ganglion activation is calcitonin-gene related peptide (CGRP). CGRP modulates pains signals, mediates inflammation in the brain, and has cardiovascular, functions among other roles 3,12. There is evidence that CGRP initiates and maintains the sensitization of trigeminal ganglion and is involved in signaling between trigeminal nerves3,13. Further, intravenous administration of CGRP triggers a migraine in migraine patients but not in healthy individuals, suggesting CGRP plays a key role in migraines10. Additionally, CGRP causes blood vessels surrounding the brain to dilate, meaning they expand however, the contribution of blood vessel expansion in migraine pain is disputed14.
Scientists have identified several changes in brain function before and during a migraine that contribute to migraine pain. With all this known, how are migraines treated and how do these treatments work?
A popular and effective treatment for migraines during an active attack are triptans. Triptans act on serotonin receptors. Serotonin is a chemical messenger within our brain responsible for a variety of functions, including mood and digestion. When triptans act on serotonin receptors, they inhibit pain neurotransmission in the trigeminal ganglion, inhibit the release of pain-promoting neuropeptides (like CGRP!), and constrict blood vessels15. Given what we know about headaches, this drug works by halting the cascade of events that occur during a migraine including sensitization, hyperexcitability, and neuropeptide release.
Overall, we’ve uncovered changes in brain signaling that occur before and during a migraine, along with a current treatment. Even though the brain itself cannot feel any pain, it plays a critical role in communicating pain to different parts of your body!
References
Cover photo by Robin Higgins from Pixabay
Figures created with BioRender.com.
On June 16 th, 2022, Tabitha Orth, President and Founder of International Autoimmune Encephalitis Society officially became the 7,315 th “point of light”. Recognized for the volunteer work she and IAES has done to spark change and improve the world for those touched by Autoimmune Encephalitis. The award was founded by President George H.W. Bush in 1990.
Become an Advocate by sharing your story. It may result in accurate diagnosis for someone suffering right now who is yet to be correctly identified. Submit your story with two photos to IAES@autoimmune-encephalitis.org
International Autoimmune Encephalitis Society (IAES), home of the AEWarrior®, is the only Family/Patient-centered organization that assists members from getting a diagnosis through to recovery and the many challenges experienced in their journey. Your donations are greatly appreciated and are the direct result of IAES’ ability to develop the first product in the world to address the needs of patients, Autoimmune Encephalitis Trivia Playing Cards. Every dollar raised allows us to raise awareness and personally help Patients, Families, and Caregivers through their Journey with AE to ensure that the best outcomes can be reached. Your contribution to our mission will help save lives and improve the quality of life for those impacted by AE.
Our website is not a substitute for independent professional medical advice. Nothing contained on our website is intended to be used as medical advice. No content is intended to be used to diagnose, treat, cure or prevent any disease, nor should it be used for therapeutic purposes or as a substitute for your own health professional's advice. Although THE INTERNATIONAL AUTOIMMUNE ENCEPHALITIS SOCIETY provides a great deal of information about AUTOIMMUNE ENCEPHALITIS, all content is provided for informational purposes only. The International Autoimmune Encephalitis Society cannot provide medical advice.
International Autoimmune Encephalitis Society is a charitable non-profit 501(c)(3) organization founded in 2016 by Tabitha Andrews Orth, Gene Desotell and Anji Hogan-Fesler. Tax ID# 81-3752344. Donations raised directly supports research, patients, families and caregivers impacted by autoimmune encephalitis and to educating healthcare communities around the world. Financial statement will be made available upon request.
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