The Clinical Challenge of Autoimmune Psychosis: Learning from Anti-NMDA Receptor Autoantibodies

Schizophrenia is a heterogeneous and complex psychiatric disorder affecting up to 1% of the population worldwide (1). Although the precise development of schizophrenia is not yet fully understood, it is now admitted to be underpinned by the entanglement of genetic, environmental, and immuno-inflammatory factors. Among schizophrenic patients, it is assumed that at least 30% will not respond to conventional antipsychotics (2). These data underlie the importance of precision medicine in psychiatry, in other words, the need to identify subgroups of patients with specific signatures who will benefit from treatment targeting these specific biological pathways. Reviving an area of exploration older than a century, recent and abundant literature emphasized the importance of the immune system in the pathophysiology of schizophrenia [for review, see Ref. (3)]. In psychiatry, the link between psychotic disorders, particularly schizophrenia, and immune system deregulations, including autoimmunity, is an old concept that regained strong support; thanks to the better characterization of brain inflammation-induced psychotic symptoms and autoimmune encephalitis (3). Moreover, recent epidemiological studies evidenced a high prevalence of multiple autoimmune diseases in schizophrenic patients (4). In a recent meta-analysis, autoantibodies against neuronal receptors have indeed been identified in the circulation of patients with neuropsychiatric disorders, constituting, today, one of the hottest topics in psychiatry (5–10). This new era fosters debate on (i) how to explain the increased burden of autoimmunity in schizophrenia, (ii) what could be the precise target(s) and the pathogenic implication(s) of the autoantibodies on the disease onset and development, (iii) how to define patient subgroups carrying such autoantibodies to facilitate their diagnosis, and (iv) how should we treat these patients using appropriate protocols such as immunotherapy (i.e., corticotherapy or plasmapheresis). Several neurological autoimmune diseases are, for instance, efficiently treated once autoantibodies against neurotransmitter receptors and ion channels have been identified (11, 12). The discovery of the autoimmune encephalitis due to anti-N-methyl-d-aspartic acid receptor (NMDAR) has greatly revived the relationship between autoimmunity and psychosis. Indeed, directed against the NMDAR N-methyl-d-aspartate receptors antibodies (NMDAR-Ab), the autoantibodies are directly responsible for the psychotic symptoms and catatonia, followed by profound neurologic deterioration (13, 14). In patients with schizophrenia, the prevalence and clinical significance of circulating NMDAR-Ab remains controversial with detection prevalence rates varying considerably between studies (15–27). Inspite of such imprecisions, defining and isolating seropositive patients, suffering from “autoimmune psychosis,” is a major challenge for appropriate treatments. In this review, we focus our attention on the potential elements possibly helping to define an “autoimmune psychosis” subgroup of schizophrenic patients. Furthermore, we outline some of the specific clinical presentation of these patients that will be of great importance to optimize the diagnostic and subsequent therapies.