The mild encephalitis (ME) hypothesis of severe mental disorders, ME to be caused by infections, autoimmunity , toxicity and trauma ( Bechter 2001, updated Bechter 2013), is now emergingly supported from neuroimaging and CSF and postmorten findings.

Review about the present status of ME hypothesis and autoimmune psychosis and remainig challenges to assess and categorize mild neuroinflammation.

expert review

Autoimmune Encephalitis presenting with exclusive psychiatric symptoms and all cases of Autoimmune Psychosis (international consensus criteria in Pollak et al, Lancet Psychiatry, 2020) match the proposed ME criteria ( Bechter 2001 & 2013). Majority of these cases of an autoimmune type of ME are well treatable with immune modulatory treatments. It remained unclear, whether CNS antibodies are causal or contributive by shaping the observed clinical syndrome. The increasing evidence of mild neuroinflammation present in considerable subgroup of schizophrenia or psychosis spectrum cases from ongoing clinical studies, including CSF ( Bechter et al 2010, Endres et al 2018, 2020, aso.) and neuroimaging plus the observed clinical improvement with immune modulytory therapies, strongly support ME hypothesis, potentialy even in considerably larger subgroup of SMDs,supported by brain biopsy (Najjar et al ,several papers) and post mortem studies (Bogerts et al group ,Weickert et al group, several papers).

Beyond ME even more refined categories of mild neuroinflammation, including parainflammation ( proposed by Medzhitov 2008) and neuroprogression ( proposed by Berk et al 2010/11) need to be considered in further research on the possible role of mild neuroinflammation in SMDs (Bechter 2020, Frontiers Psychiatry).

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Patients with anti-N-methyl-d-aspartate (NMDA) receptor encephalitis (ANMDARE) show a wide range of behavioral abnormalities and are often mistaken for primary psychiatric presentations. We aimed to determine the behavioral hallmarks of ANMDARE with the use of systematic neuropsychiatric and cognitive assessments.

A prospective study was conducted, with 160 patients admitted to the National Institute of Neurology and Neurosurgery of Mexico, who fulfilled criteria for possible autoimmune encephalitis and/or red flags along a time window of seven years. Cerebrospinal fluid (CSF) antibodies against the NR1 subunit of the NMDAR were processed with rat brain immunohistochemistry and cell-based assays with NMDA expressing cells. Systematic cognitive, neuropsychiatric, and functional assessments were conducted before knowing NMDAR antibodies results. A multivariate analysis was used to compare patients with and without definite ANMDARE according to antibodies in CSF.

After obtaining the CSF antibodies results in 160 consecutive cases, 100 patients were positive and classified as having definite ANMDARE. The most frequent neuropsychiatric patterns were psychosis (81%), delirium (75%), catatonia (69%), anxiety-depression (65%), and mania (27%). Cognition was significantly impaired. A total of 34% of the patients had a predominantly neuropsychiatric presentation without seizures. After multivariate analysis, the clinical hallmarks of ANMDARE consisted of a catatonia–delirium comorbidity, tonic-clonic seizures, and orolingual dyskinesia.

Our study supports the notion of a neurobehavioral phenotype of ANMDARE characterized by a fluctuating course with psychotic and affective symptoms, catatonic signs, and global cognitive dysfunction, often accompanied by seizures and dyskinesia. The catatonia–delirium comorbidity could be a distinctive neurobehavioral phenotype of ANMDARE.

Autoimmune mechanisms are related to disease development in a subgroup of patients with psychosis. The contribution of immunoglobulin G (IgG) antibodies against myelin oligodendrocyte glycoprotein (MOG) is mainly unclear in this context.

Therefore, two patients with psychosis and anti-MOG antibodies – detected in fixed cell-based and live cell-based assays – are presented.

Patient 1 suffered from late-onset psychosis with singular white matter lesions in magnetic resonance imaging (MRI) and intermittent electroencephalography (EEG) slowing. Patient 2 suffered from a chronic paranoid–hallucinatory disorder with intermittent confusional states, non-specific white matter alterations on MRI, a disorganised alpha rhythm on EEG, and elevated cerebrospinal fluid protein. Both patients had anti-MOG antibody titres of 1 : 320 in serum (reference < 1 : 20).

The arguments for and against a causal role for anti-MOG antibodies are discussed. The antibodies could be relevant, but due to moderate titres, they may have caused a rather ‘subtle clinical picture’ consisting of psychosis instead of ‘classical’ MOG encephalomyelitis.

Autoimmune encephalitis (AE) is an important consideration during the diagnostic work-up of secondary mental disorders. Indeed, isolated psychiatric syndromes have been described in case reports of patients with underlying AE. Therefore, the authors performed a systematic literature review of published cases with AE that have predominant psychiatric/neurocognitive manifestations. The aim of this paper is to present the clinical characteristics of these patients.

The authors conducted a systematic Medline search via Ovid, looking for case reports/series of AEs with antineuronal autoantibodies (Abs) against cell surface/intracellular antigens combined with predominant psychiatric/neurocognitive syndromes. The same was done for patients with Hashimoto encephalopathy/SREAT. Only patients with signs of immunological brain involvement or tumors in their diagnostic investigations or improvement under immunomodulatory drugs were included.

We identified 145 patients with AE mimicking predominant psychiatric/neurocognitive syndromes. Of these cases, 64% were female, and the mean age among all patients was 43.9 (±22.1) years. Most of the patients had Abs against neuronal cell surface antigens (55%), most frequently against the NMDA-receptor (N = 46). Amnestic/dementia-like (39%) and schizophreniform (34%) syndromes were the most frequently reported. Cerebrospinal fluid changes were found in 78%, electroencephalography abnormalities in 61%, and magnetic resonance imaging pathologies in 51% of the patients. Immunomodulatory treatment was performed in 87% of the cases, and 94% of the patients responded to treatment.

Our findings indicate that AEs can mimic predominant psychiatric and neurocognitive disorders, such as schizophreniform psychoses or neurodegenerative dementia, and that affected patients can be treated successfully with immunomodulatory drugs.