Autoimmune
encephalopathy represents a complex category of disease with diverse immunologic associations, clinical manifestations, and therapeutic outcomes. Three main subgroups include autoimmune
encephalopathies without
cancer but with neural nonspecific serologic evidence of autoimmunity (encompassing "
Hashimoto's encephalopathy") that is the main focus of this review, paraneoplastic
encephalopathies, and central nervous system (
CNS) vasculitis (primary or secondary). Diagnosis of autoimmune
encephalopathy can be suspected based on the
clinical course, serologic evidence of autoimmunity, severe but nonspecific slowing on electroencephalography, and evidence of intrathecal
inflammation in the cerebrospinal fluid. Rarely, there will be evidence of meningeal enhancement or increased fluid attenuated inversion-recovery signal in symptomatic regions on magnetic resonance imaging, but diagnosis may require brain biopsy demonstration of perivascular lymphocytic infiltrates. Nonspecific autoimmune
encephalopathies are generally much more therapeutically responsive than paraneoplastic and vasculitic
encephalopathies, so that high-dose
corticosteroids may produce dramatic improvement within as little as a few days, although exceptional patients can require months of
therapy.
Paraneoplastic syndromes typically require
tumor removal and often prove fatal. CNS
vasculitides may respond to
steroid therapy, but often require a second agent such as
cyclophosphamide.