Searching for Neuronal Antibodies in Psychiatric Diseases: Uncertain Findings and Implications

Seroprevalence of neuronal antibodies in diseases mimicking autoimmune encephalitis

Detection of neuronal antibodies for autoimmune encephalitis and paraneoplastic neurological syndromes relies on commercially available cell-based assays and lineblots. However, lineblots may reveal the presence of neuronal antibodies in patients with various non-autoimmune etiologies. Herein we describe patients with non-autoimmune etiologies (cohort B) and detectable neuronal antibodies and compare them to definite cases of autoimmune encephalitis (cohort A) for differences in clinical data. All patients positive for at least one neuronal antibody were retrospectively evaluated for autoimmune encephalitis and/or paraneoplastic neurological syndrome between 2016 and 2022. 39 cases in cohort B and 23 in cohort A were identified. In cohort B, most common diagnoses were neurodegenerative disorders in 9/39 (23.1%), brain tumors in 6/39 (15.4%) while most common detected antibodies were anti-titin (N10), anti-recoverin (N11), anti-Yo (N8) and all were detected in serum only. Differential aspects between cohort A and B were CSF pleocytosis (14/23 (60.8%) vs 11/35 (31.4%), p = 0.042, respectively), MRI features suggestive of encephalitis (6/23 (26.1%) vs 0 (0%), p = 0.002, respectively) and epilepsy restricted to temporal lobes (14/23 (60.9%) vs 2/30 (6.7%), p = 0.0003, respectively). A large proportion of lineblot results were non-specific when only serum was tested and were frequently found in non-autoimmune neurological conditions.

Blood and CSF anti-neuronal antibodies testing in psychotic syndromes: a retrospective analysis from a tertiary psychiatric hospital

A Consensus of Psychoimmunology Experts (Pollak et al., 2019) established a set of red flags and proposed diagnostic criteria for psychosis of autoimmune origin (AIP). Previous studies on AIP are limited by the scarcity of CSF analysis, preventing the valorization of blood anti-neuronal antibodies (Ab). The aims of this study are to determine the relative frequency and characterize AIP in a cohort of psychotic patients that underwent CSF workup. This work is a retrospective study in a tertiary psychiatric hospital. Clinical and paraclinical data were collected from medical records, and patients were classified according to Pollak et al. (2019) criteria. From 68 patients, ten (14.7%) had positive anti-neuronal antibodies (Ab): n = 5 in CSF and blood (n = 4 anti-NMDAr, n = 1 -GAD65), and n = 5 in blood only (n = 1 anti-GABAb, n = 1 -GAD65, n = 1 -SOX1, n = 1 -NMDAr, n = 1 -zic4). After 5- (2-10)-year follow-up, n = 6/68 (8.8%) had AIP diagnosis in context of autoimmune encephalitis (AE), and the remaining (n = 4/10, blood-only Ab) alternative diagnoses (n = 2 dementia, n = 1 schizophrenia, n = 1 intellectual disability). Ten of the 13 patients that fulfilled criteria for possible AIP were mimics, and only three AE had criteria for probable AIP. All AIP developed neurological manifestations (mostly cognitive dysfunction); EEG was usually abnormal (66.7%), and all had normal MRI. We found statistically significant associations between AIP/AE and systemic autoimmune disease, presentation with seizures and EEG abnormalities. All AE developed neurological symptoms alongside psychosis. Ab positivity occurred predominantly in AE but also in other neuropsychiatric disorders. Clinical suspicion based on the knowledge of the described presentations of established Ab is crucial in the psychotic patient approach.

SOX1 Antibody in a Patient With Serotonin Syndrome

SOX1 antibody is an autoimmune antibody, usually associated with Lambert-Eaton myasthenic syndrome, paraneoplastic conditions, and encephalitis. This antibody has also been found among psychiatric patients. However, the role of SOX1 antibody in serotonin syndrome has not yet been defined, as a literature search yielded no results. Therefore, the treatment as such has unknown clinical significance. In this case study, we report a patient with SOX1 antibodies and altered mental status out of proportion to serotonin syndrome whose symptoms improved with simultaneous treatment of both conditions.