Autoimmune encephalitis (acute disseminated encephalomyelitis, ADEM)

Autoimmune encephalitis (AE) occurs when healthy cells and tissues in the brain or spinal cord are attacked by the body’s immune system, leading to inflammation. AE is a collection of conditions. Some forms are associated with specific antibodies targeting nerve cells, while others, like acute disseminated encephalomyelitis (ADEM), are immune-mediated conditions that primarily affect myelin in the central nervous system. In many cases, the exact cause is unknown, although some forms may be triggered by infections or associated with tumors. In certain cases, particularly paraneoplastic forms, the immune response may be linked to an underlying cancer and involve T-cell–mediated damage to neurons.

AE can be difficult to diagnose due to overlapping clinical symptoms, imaging findings, and laboratory results with other conditions, particularly infectious encephalitis, and the lack of a single definitive diagnostic test.

Acute disseminated encephalomyelitis (ADEM) is an immune-mediated condition that causes widespread inflammation and damage to myelin in the brain and spinal cord. It most often occurs following an infection, particularly in children, although the exact cause is not always known.

ADEM is thought to result from an abnormal immune response in which the body mistakenly targets components of the central nervous system. Proposed mechanisms include molecular mimicry, disruption of the blood–brain barrier, and broader neuroinflammatory processes.

ADEM is typically described as a monophasic condition, meaning it occurs as a single episode. However, multiphasic forms have been reported, and distinguishing ADEM from other demyelinating diseases such as multiple sclerosis can be challenging.

Autoimmune rhombencephalitis is a rare form of autoimmune encephalitis that causes inflammation in the brainstem (also called the rhombencephalon). The immune system mistakenly attacks this region, leading to neurological symptoms that affect movement, speech, swallowing, and eye coordination. Autoimmune rhombencephalitis may be associated with specific autoantibodies, including anti-Ma2, anti-Hu, and anti-GAD, or it may develop as part of a paraneoplastic syndrome related to an underlying cancer.

Autoimmune encephalitis: Impaired memory and cognition, abnormal movements, seizures, and/or problems with balance, speech, or vision, psychosis, aggression, inappropriate sexual behaviors, panic attacks, compulsive behaviors, euphoria, or fear.

ADEM: Fever, headaches, irritability, fatigue, lethargy, malaise, unintended weight loss, nausea, and vomiting, vision loss in one or both eyes, muscle weakness even to the point of paralysis, difficulty coordinating voluntary muscle movements, confusion, stupor, delirium, and potentially coma.

Autoimmune rhombencephalitis: Dizziness, difficulty speaking (dysarthria), trouble swallowing (dysphagia), double vision (diplopia), loss of coordination (ataxia), facial paralysis, limb weakness, abnormal eye movements, confusion, and, in severe cases, respiratory failure or coma.

Autoimmune encephalitis: Multiple sclerosis, Hashimoto’s thyroiditis, and vasculitis. 

ADEM: In some cases, distinguishing ADEM from other demyelinating conditions such as multiple sclerosis or MOG antibody-associated disease can be difficult, particularly early in the disease course.

Autoimmune rhombencephalitis: May occur alongside or be triggered by other autoimmune or immune-mediated diseases, including:

• Paraneoplastic syndromes, especially those linked to small cell lung cancer, testicular cancer, or other malignancies
• Neuromyelitis optica spectrum disorder
• Multiple sclerosis
• Anti-GAD antibody syndromes, such as stiff person syndrome
• Other forms of autoimmune encephalitis, such as anti-NMDA receptor encephalitis

Autoimmune encephalitis may be triggered by infections, particularly herpes simplex virus,  as well as by other infectious causes. It can also be associated with underlying tumors (paraneoplastic syndromes) or occur in individuals with immune system dysfunction, including those with HIV.

ADEM most commonly occurs after an infection, often developing within one to two weeks. While many cases follow viral illness, other triggers have been reported, and individual susceptibility, potentially influenced by genetic factors, may also play a role.

Autoimmune rhombencephalitis is rare and most often associated with paraneoplastic syndromes or other autoimmune conditions mentioned above. The presence of specific autoantibodies, such as anti-Ma2, anti-Hu, or anti-GAD, is strongly associated with increased risk.

Additional encephalitis resources can be found at https://www.encephalitis411.org/

• Acute Disseminated Encephalomyelitis (ADEM): Current View into Etiopathogenesis and Clinical Features (2026)
• Clinical and Autoimmune Profiles of Omani Patients with True Versus False Positive Autoimmune Encephalitis Antibodies Panels (2025)
• Autoimmune Rhombencephalitis as a Presentation of Post-COVID-19 Syndrome: A Case Report (2025)
• [Autoimmune encephalitis-An update] (2023)
• Autoimmune encephalitis: recent clinical and biological advances (2023)
• Acute disseminated encephalomyelitis (ADEM) following recent Oxford/AstraZeneca COVID-19 vaccination (2022)
• Autoimmune encephalitis associated with COVID-19: A systematic review (2022)
• Rhombencephalitis with longitudinal extensive transverse myelitis in lupus: an overlap syndrome? (2023)
• Rhombencephalitis in Pregnancy-A Challenging Case of Probable Listeria Infection (2022)