Researchers are identifying an increasing number of antibodies that are the culprit behind seizure disorders in adults.
There’s now a “very big list” of such antibodies that target the inside or the outside of the neuronal cell, said Claude Steriade, MD, Division of Neurology, University of Toronto, Ontario, Canada.
“Over the past few years, there has been increasing recognition that some forms of epilepsy are immune mediated; they’re associated with antibodies that target neurons,” said Dr Steriade.
At a press briefing during the American Epilepsy Society (AES) 69th Annual Meeting here, Dr Steriade presented a study illustrating that different antibodies can lead to very different diseases.
It’s well known that antineuronal antibodies cause a variety of neurologic symptoms, from gait and coordination difficulties to rapidly progressing dementia, as well as seizures, said Dr Steriade. But it’s only recently that researchers are recognizing that epilepsy can be the predominant feature, she said.
It’s not clear how these antibodies get triggered, although some cases are associated with an underlying tumor that the immune response targets.
“As a side effect of this immune response, antibodies are created that then cross the blood-brain barrier, recognize proteins within the brain, and cause cerebral dysfunction,” explained Dr Steriade.
Not all these antibodies are the same, however. Some target proteins inside the cell (intracellular antigens) and others target proteins on the surface of the cell (cell-surface receptor antigens).
Immunologic factors appear to separate these two types of antibodies. Those that target intracellular antigens are associated with a T-cell immune response and with cancer, while the ones targeting proteins on the cell surface are typically associated with a B-cell response and are not associated with an underlying cancer.
“The difference between these antibodies in terms of their immunology translates into different clinical pictures and different treatment response,” said Dr Steriade.
Researchers are identifying an increasing number of antibodies that are the culprit behind seizure disorders in adults.
There’s now a “very big list” of such antibodies that target the inside or the outside of the neuronal cell, said Claude Steriade, MD, Division of Neurology, University of Toronto, Ontario, Canada.
“Over the past few years, there has been increasing recognition that some forms of epilepsy are immune mediated; they’re associated with antibodies that target neurons,” said Dr Steriade.
At a press briefing during the American Epilepsy Society (AES) 69th Annual Meeting here, Dr Steriade presented a study illustrating that different antibodies can lead to very different diseases.
It’s well known that antineuronal antibodies cause a variety of neurologic symptoms, from gait and coordination difficulties to rapidly progressing dementia, as well as seizures, said Dr Steriade. But it’s only recently that researchers are recognizing that epilepsy can be the predominant feature, she said.
It’s not clear how these antibodies get triggered, although some cases are associated with an underlying tumor that the immune response targets.
“As a side effect of this immune response, antibodies are created that then cross the blood-brain barrier, recognize proteins within the brain, and cause cerebral dysfunction,” explained Dr Steriade.
Not all these antibodies are the same, however. Some target proteins inside the cell (intracellular antigens) and others target proteins on the surface of the cell (cell-surface receptor antigens).
Immunologic factors appear to separate these two types of antibodies. Those that target intracellular antigens are associated with a T-cell immune response and with cancer, while the ones targeting proteins on the cell surface are typically associated with a B-cell response and are not associated with an underlying cancer.
“The difference between these antibodies in terms of their immunology translates into different clinical pictures and different treatment response,” said Dr Steriade.
Different Immune Responses
However, response to immune suppressants, such steroids, intravenous immunoglobulins, plasma exchange, or rituximab, was different. MA2 patients responded poorly to these drugs, while those with LGI1 antibodies responded quite well.
Which patients should be tested for antibodies? According to Dr Steriade, those with “explosive” late-onset (over age 40 years) resistant epilepsy with atypical psychiatric features, such as psychosis.
Certain radiologic features, such as edema, may also be suggestive, she said.
Having other coexisting autoimmune diseases, such as type 1 diabetes, might offer another clue, said Mar Carreño, MD, PhD, professor and epileptologist, Hospital Clinic, Barcelona, Spain.
Dr Carreño’s own study of 13 patients with drug-resistant epilepsy due to autoimmune encephalitis showed that surgery may be a good option. She and her colleagues also showed that there was no apparent correlation between antibody type (they looked at anti-MA2, anti-LGI1, and four others).
Invited to comment on this research, Jeffrey W. Britton, MD, professor of neurology, and chair, Division of Epilepsy, Mayo Clinic, Rochester, Minnesota, agreed that seizure disorders caused by autoimmune mechanisms are increasingly being recognized. Technological advances, he said, have led to the discovery of more neuronal antibody types.
Dr Britton attributed much of the increased awareness surrounding autoimmune epilepsies to the publication of Brain on Fire, journalist Susannah Cahalan’s best-selling account of her autoimmune encephalitis and seizures.
The new study confirms previous observations made by other investigators, including Dr Britton’s group. “We also found that the potential for response to immunotherapy is greater for autoimmune epilepsies due to antibodies targeting neuronal surface structures than for those targeting intracellular proteins.”
The exact prevalence of autoimmune causes of epilepsy is not known. According to Dr Britton, a few studies have suggested that neurologic antibodies are present in 1% to 5% of patients with seizures.
“However, these antibodies, especially when present at low levels, are sometimes coincidental and not causative of the epilepsy,” he said.
Dr Steriade estimated that 5% to 10% of all drug-resistant focal epilepsies are linked to antibodies.
American Epilepsy Society (AES) 69th Annual Meeting. Abstracts 3.153 and 2.320.
Source: MedScape by P. Anderson
