Originally, the term described a clinical focal point syndrome. Limbic encephalitis (LE): LE has developed in the context of paraneoplastic encephalitis, which has been known for some time and has undergone a change in meaning in the discourse of the last decade. Because antineuronal autoantibodies (Abs) can now be detected, cases of encephalopathy not previously recognized as neuroinflammatory can comply with the criteria of autoimmune encephalitis. The term has also been used when secondary brain damage was assumed, but the exact mechanism of the disease remained unclear (e.g., hepatic or epileptic encephalopathy). The changing nomenclature for autoimmune neuropsychiatric phenomena is summarized in Box 1.Įncephalopathy: Traditionally, this term has been used mainly for persistent brain damage. For AE with predominant psychotic symptoms, the term “autoimmune psychosis” (AP) was recently suggested. In most cases that are positive for antineuronal Abs, patients develop clear neurological symptoms in the course of the disease, such as dystonic movement disorders or epileptic seizures. In a German case series of 100 patients with different forms of AEs with Abs against antineuronal antigens, over half of the patients (60%) presented with psychotic symptoms. Because these syndromes can be accompanied by polymorphic psychotic symptoms, immunological concepts of schizophreniform psychoses have gained considerable attention since. Since then, a large number of other antineuronal Abs against cell surface antigens and their associated syndromes have been identified. In 2007, the field of autoimmune encephalitis (AE) was redefined with the first description of anti-NMDA-R encephalitis. Such secondary forms can be linked to autoantibody (Ab)-associated autoimmune processes such as anti- N-Methyl- d-aspartate receptor encephalitis. Secondary forms are based on clearly identifiable causes in the sense of etiology or according to recognizable pathogenesis. Large, genome-wide studies have identified over 100 distinct gene sites that contribute to the relative risk of psychotic symptoms. Primary schizophreniform psychoses are caused by a complex interaction between multiple genes and environmental factors. Schizophrenia and other psychotic disorders are severe and frequent conditions characterized by delusions, hallucinations, disorganization, formal thinking changes, catatonia, and different negative symptoms typically occurring for the first-time during adolescence and early adulthood. The detection of clinical and/or paraclinical pathologies (e.g., pleocytosis in CSF) in combination with antineuronal Abs and the exclusion of alternative causes may lead to the diagnosis of AE/AP and enable more causal therapeutic immunomodulatory opportunities. Beyond, tissue-based assays on brain slices of rodents may detect previously unknown antineuronal Abs in some cases. Less frequent antineuronal Abs (e.g., against DPPX, GABA A-R, glycine-R, IgLON5) can be investigated in the second step when first step screening is negative and/or some specific clinical factors prevail. The antibody analyses in these patients include the testing of the most frequently found Abs against cell surface antigens (NMDA-R, CASPR2, LGI1, AMPA-R, GABA B-R), intracellular antigens (Hu, Ri, Yo, CV2/CRMP5, Ma2, amphiphysin, GAD65), thyroid antigens (TG, TPO), and antinuclear Abs (ANA). Paraclinical alterations that can be observed in patients with AE/AP are inflammatory cerebrospinal fluid (CSF) pathologies, focal or generalized electroencephalographic slowing or epileptic activity, and/or suspicious “encephalitic” imaging findings. The term autoimmune psychosis (AP) was recently suggested for these patients. Predominant psychotic courses of AEs have also been described casuistically. Typical clinical signs for AEs are the acute onset of paranoid hallucinatory symptoms, atypical polymorphic presentation, psychotic episodes in the context of previous AE, and additional neurological and medical symptoms such as catatonia, seizure, dyskinesia, and autonomic instability. Over the course of the disease, other neurological phenomena, such as epileptic seizures, movement disorders, or reduced levels of consciousness, usually arise. These newly described secondary, immune-mediated schizophreniform psychoses typically present with the acute onset of polymorphic psychotic symptoms. The secondary or “symptomatic” forms of psychosis have reentered the focus stimulated by the discovery of autoantibody (Ab)-associated autoimmune encephalitides (AEs), such as anti-NMDA-R encephalitis, which can at least initially mimic variants of primary psychosis. Secondary forms are based on a clearly identifiable organic cause, in terms of either an etiological or a relevant pathogenetic factor. Primary schizophreniform psychoses are thought to be caused by complex gene–environment interactions.
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