This umbrella term summarizes a number of clinical syndromes whose common denominator is a cellular and/or humoral immune reaction against central and/or peripheral nervous tissue. Symptoms depend on the brain region affected, e.g., limbic encephalitis when hippocampal/limbic areas are preferentially affected, ataxia/dysarthria when cerebellum is involved.
In recent years, a group of encephalitis has been characterized whose common denominators are, first, the detection of autoantibodies to synaptic components, for example, the N-methyl-D-aspartate receptor (NMDAR), and, second, a response to immunosuppressive therapies. This new group of disorders is termed antibody-mediated autoimmune encephalitis. Since 2007, more than 14 specific neuronal/glial autoantibodies have been detected and the associated syndromes may be reclassified as autoimmune encephalitis.
Basically, a distinction is currently made between antibodies against intracellular antigens and neuronal surface antigens. Furthermore, immune reactions triggered by a tumor (paraneoplastic syndromes) and idiopathic syndromes without tumor detection are differentiated. While autoimmune encephalitis with evidence of antibodies against intracellular neuronal antigens are usually associated with a tumor ("paraneoplastic") and respond to immunotherapy only to a limited extent, those with antibodies against membrane-bound neuronal antigens often occur independently of a tumor ("non-paraneoplastic" or idiopathic) and may often be treated successfully with immunotherapy.
The detection of neuronal/glial surface autoantibodies not only has prognostic and therapeutic significance, but also represents a paradigm shift in neuroimmunology. The autoantibodies lead via direct interaction with the target antigen without cellular or humoral destruction to a mostly reversible antagonization of the synaptic target structure and thus to neurological symptoms.