Histopathology of autoimmune encephalitis

Background. Within the spectrum of new onset epilepsies, autoimmune encephalitis is becoming increasingly important as a differential diagnosis. Objectives. Does the neuropathological examination of brain tissue, e.g. from epilepsy surgery provide typical or even pathognomonic correlates of autoimmune encephalitis of different origin? Materials andmethods. Analysis of literature and own observations. Results. With respect to many forms of autoimmune encephalitis, only a limited number of scientific publications of neuropathological findings are available. With respect to Rasmussen encephalitis, neuropathological alterations allow a distinction of four different stages. The neuropathological findings support cytotoxic damage of affected neurons. Autoimmune encephalitic reactions with antibodies against intracellular or neuronal surface antigens represent heterogeneous histopathological patterns. Here, a varying quantity and composition of the inflammatory cell infiltrates as well as differences in the activation of the complement system is reported in the available literature for different disease-causing antibodies. In encephalitis, which is associated with antibodies against intracellular target structures, cytotoxic inflammatory reactions dominate. In limbic encephalitis with antibodies against structures of the potassiumchannel complex, complement activation is often present. Both aspects, i.e. presence of T-lymphocytes and complement system activation, are less frequent or lacking in NMDAR-encephalitis. Conclusions. Neuropathological findings can strongly support the finding of a definite diagnosis concerning the cause of inflam-matory-mediated epilepsy. Furthermore, histopathological analyses can provide important information for the improved understanding of the etiology and pathogenesis of different forms of autoimmune encephalitis. Currently, the comparability of the published neuropathological cases of autoantibodypositive patients with epilepsies is limited with respect to the strong heterogeneity of the duration of disease before neurosurgery, differences with respect to medication and also analyzed areas of the brain.