Rasmussen’s Encephalitis: Managing Seizures and Brain Inflammation

Oct 11

6 min read

Updated: 3 days ago

Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026

Definition: Rasmussen’s encephalitis is an extremely rare neurological condition characterized by chronic inflammation in one half of the brain.
Who it affects: Primarily children between ages 2 and 10.
Course: Frequent, intractable seizures and progressive brain damage, leading over time to mental decline and weakness or paralysis on one side of the body.
Treatment: There is no cure, but immunotherapy and hemispherectomy (surgical disconnection of the affected brain half) are used to manage symptoms and prevent further damage.

Quick Answer

Rasmussen's encephalitis is a rare inflammatory brain disorder that affects only one hemisphere of the brain, causing frequent, severe seizures, mental decline and progressive paralysis on one side of the body. It most commonly affects children under 10. Its exact cause is unknown, possibly autoimmune or viral. Treatment manages seizures and inflammation through medication or surgery. ^[1]

What the research says

Hemispheric surgery stops seizures in most patients, but the benefit can fade over time. In a series of 30 patients who underwent 35 hemispherectomies, the Kaplan-Meier seizure-freedom rate was 81.5%, 63.6% and 55.6% at 1, 5 and 10 years after surgery. Complete disconnection of the diseased hemisphere improved seizure freedom (P = .021), and reoperation led to seizure freedom in every case (Sundar et al., Neurosurgery, 2022).
Earlier surgery is linked to better long-term seizure control. An individual participant data meta-analysis of 21 studies (158 patients) found that 77.8% (123 of 158) achieved seizure freedom at longest follow-up. A shorter seizure duration before surgery was an independent predictor of seizure freedom (HR 0.54, P = 0.044), and cognitive and motor outcomes were stable or improved in 70.1% and 85.1% of patients. The authors cautioned that small sample size and bias limit the findings (Lv et al., Neurosurg Rev, 2026).
Rasmussen’s encephalitis can also begin in adolescents and adults, often with a milder course. A systematic review of 50 papers identified 102 late-onset patients (about 8 women for every 2 men). Compared with classic childhood-onset disease, late-onset cases had a slower evolution, less cognitive deterioration and a better outcome, and immunomodulatory therapies improved 61% of patients (Dupont et al., Autoimmun Rev, 2017).

What is Rasmussen's encephalitis?

Rasmussen’s encephalitis (RE), also known as Rasmussen syndrome, is a progressive neurological disorder defined by chronic inflammation of one brain hemisphere. This localized inflammation leads to permanent brain damage and a loss of function in the affected half. The condition is named after Theodore Rasmussen, the physician who first described the syndrome in 1958. It is exceptionally rare, with researchers estimating it affects only about two out of every 10 million people. ^[1]

While the condition most frequently begins in children between the ages of 2 and 10, it can also manifest in adolescents and adults. The hallmark of the disease is the combination of frequent seizures and a steady decline in motor and cognitive abilities tied to the affected side of the brain.

Feature	Rasmussen’s Encephalitis Characteristics
Primary Target	One hemisphere (half) of the brain.
Prevalence	Approximately 2 in 10 million people.
Common Age Group	Children aged 2 to 10 years.
Key Symptoms	Frequent seizures, one-sided weakness, mental decline.
Long-term Outcome	Permanent neurological damage and atrophy.

What are the symptoms of Rasmussen's encephalitis?

The progression of Rasmussen’s encephalitis typically begins with a seizure, which can take several forms. Some patients experience generalized tonic-clonic seizures involving the whole body, while others have focal aware seizures where they remain conscious but experience localized twitching.

Early and Progressive Signs

In addition to seizures, mild weakness in an arm or leg is often one of the first indicators. As the inflammation persists, the seizures typically become frequent and difficult to control with standard medications. Approximately half of those affected develop epilepsia partialis continua (EPC), a state where seizures occur every few seconds or minutes. Within months to a year of the initial onset, more severe neurological symptoms usually emerge, including:

Mental Decline: Significant challenges with memory, thinking, and intellectual function.
Hemiparesis and Hemiplegia: Progressive weakness that often leads to full paralysis on one side of the body.
Aphasia: Loss of speech and language abilities, particularly if the inflammation affects the brain's language center (usually the left hemisphere).
Hemianopsia: Loss of vision in half of the visual field.

The disease is typically most aggressive during the first 8 to 12 months. After this period, the progression often slows or stops, though the resulting damage to the brain tissue is permanent. ^[1]

Infographic of the three stages of Rasmussen’s encephalitis: initial seizure, progressive inflammation, and neurological stabilization with hemispheric atrophy. – rinnit.com — Figure 1: Progression of Rasmussen’s encephalitis, from the initial seizure to stabilization of neurological damage.

What causes Rasmussen's encephalitis?

Despite decades of study, the exact cause of Rasmussen’s encephalitis remains unknown. Current scientific theories focus on two primary possibilities. The first is an autoimmune response, where the body's immune system mistakenly attacks healthy brain tissue in one hemisphere. The second theory suggests an unknown viral infection that enters the brain and triggers localized inflammation. However, no specific virus has ever been identified in the brains of affected individuals. ^[1]

Diagram comparing the autoimmune theory and the viral infection theory of Rasmussen’s encephalitis, each leading to inflammation, neuron loss and seizures. – rinnit.com — Figure 2: The two leading theories of the cause of Rasmussen’s encephalitis: autoimmune dysfunction and viral infection.

How is Rasmussen's encephalitis diagnosed and managed?

Healthcare providers diagnose Rasmussen’s encephalitis by combining clinical symptoms with specialized testing. Magnetic resonance imaging (MRI) is essential, as it can reveal atrophy—the loss of brain tissue—in one hemisphere. A pattern of worsening atrophy over several months is a strong diagnostic indicator. Electroencephalography (EEG) is also used to record the abnormal electrical activity characteristic of the syndrome.

Treatment Strategies

Because there is no cure, treatment is focused on managing the inflammation and reducing seizure frequency.

Medication: Antiseizure drugs are used, though they are often unable to control the seizures completely.
Immunotherapy: Early intervention with immunotherapy may help manage the immune response and limit further brain damage.
Hemispherectomy: This is considered the most effective treatment for intractable seizures. It involves surgically removing or disconnecting the affected half of the brain. While it sounds drastic, many children who undergo this surgery have already lost function in that hemisphere, and the procedure can stabilize their condition and stop the seizures. ^[1]

Treatment pathway in three steps: diagnosis with MRI and EEG, management with antiseizure medication and immunotherapy, and surgical intervention with hemispherectomy. – rinnit.com — Figure 3: Treatment pathway for Rasmussen’s encephalitis, highlighting the role of hemispherectomy.

Conclusion

Rasmussen’s encephalitis is a challenging and life-altering diagnosis, particularly for the families of affected children. While the condition leads to permanent neurological damage, modern medical interventions can stabilize the disease and improve the quality of life by managing seizures. Ongoing research and clinical trials continue to explore new ways to understand and treat this rare syndrome, providing hope for better outcomes in the future.

Frequently Asked Questions

What is the first sign of Rasmussen’s encephalitis?

The first sign is typically a seizure. This can be a generalized seizure involving muscle convulsions or a focal seizure where the person remains aware but experiences localized twitching, such as in a hand or arm. Mild weakness in a limb is also a common early symptom. ^[1]

Is Rasmussen’s encephalitis an autoimmune disease?

While the exact cause is unknown, many researchers believe it is an autoimmune condition where the immune system mistakenly attacks healthy brain tissue in one hemisphere. Another theory is that it may be caused by an unidentified virus. ^[1]

How rare is Rasmussen syndrome?

Rasmussen syndrome is extremely rare, affecting approximately 2 out of every 10 million people. It most commonly affects children between the ages of 2 and 10, though it can occur in older individuals. ^[1]

What is a hemispherectomy?

A hemispherectomy is a surgical procedure where one half of the brain is either removed or disconnected from the other half. It is considered the most effective way to treat the severe, frequent seizures caused by Rasmussen’s encephalitis. ^[1]

Can Rasmussen’s encephalitis be cured?

There is currently no cure for the condition. The goal of treatment is to manage inflammation and seizures to prevent further brain damage and stabilize the patient's neurological function. ^[1]

What happens to the brain in Rasmussen’s encephalitis?

The condition causes chronic inflammation in one hemisphere, leading to atrophy or the loss of brain tissue. This damage results in progressive weakness on one side of the body and mental decline. ^[1]

What is epilepsia partialis continua (EPC)?

EPC is a condition where seizures occur every few seconds or minutes. It affects about half of the people diagnosed with Rasmussen’s encephalitis and is often resistant to standard antiseizure medications. ^[1]

Does Rasmussen’s encephalitis affect both sides of the brain?

In the vast majority of cases, it only affects one hemisphere. However, in very rare instances, the condition can progress to involve the other side of the brain. ^[1]

How do doctors diagnose Rasmussen’s encephalitis?

Diagnosis is based on a combination of symptoms, EEG results showing abnormal electrical activity, and MRI scans that show a pattern of worsening tissue loss (atrophy) in one half of the brain. ^[1]

References

Cleveland Clinic. Rasmussen’s Encephalitis. Cleveland Clinic Health Library. Accessed October 11, 2026. https://my.clevelandclinic.org/health/diseases/6092-rasmussens-encephalitis
Sundar SJ, Lu E, Schmidt ES, et al. Seizure outcomes and reoperation in surgical Rasmussen encephalitis patients. Neurosurgery. 2022;91(1):93-102. PMID: 35544031. DOI: https://doi.org/10.1227/neu.0000000000001958
Lv K, Yang Y, Wang X, et al. Preoperative predictors of seizure freedom after hemispheric surgery for Rasmussen’s encephalitis: an individual participant data meta-analysis. Neurosurg Rev. 2026;49(1). PMID: 41748938. DOI: https://doi.org/10.1007/s10143-025-04113-9
Dupont S, Gales A, Sammey S, et al. Late-onset Rasmussen encephalitis: a literature appraisal. Autoimmun Rev. 2017;16(8):803-810. PMID: 28572051. DOI: https://doi.org/10.1016/j.autrev.2017.05.022

Medical disclaimer

This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have about a medical condition.