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A 37-year-old man with a history of seminoma presented with vertigo, ataxia, and diplopia. An autoantibody specific for kelch-like protein 11 (KLHL11) was identified with the use of programmable phage display. Immunoassays were used to identify KLHL11 IgG in 12 other men with similar neurologic features and testicular disease. Immunostaining of the patient's IgG on mouse brain tissue showed sparse but distinctive points of staining in multiple brain regions, with enrichment in perivascular and perimeningeal tissues. The onset of the neurologic syndrome preceded the diagnosis of seminoma in 9 of the 13 patients. An age-adjusted estimate of the prevalence of autoimmune KLHL11 encephalitis in Olmsted County, Minnesota, was 2.79 cases per 100,000 men. (Funded by the Rochester Epidemiology Project and others.).

Objective:We sought to validate methods for detection and confirmation of GABAA receptor (R)-IgG and clinically characterize seropositive cases. Methods:Archived serum and CSF specimens (185 total) suspected to harbor GABAAR-IgG were evaluated by indirect immunofluorescence assay (IFA). Twenty-six specimens from 19 patients appeared suspicious for GABAAR-IgG positivity by IFA, based on prior reports and comparison with commercial GABAAR antibody staining. Aliquots of those specimens were tested at the University of Oxford, United Kingdom, and Euroimmun, Lubeck, Germany, for GABAAR-IgG by cell-based assays (CBAs) using HEK293-indicator cells transfected with plasmids encoding different GABAAR subunits. Results:Eight specimens (of 26 tested; 4 serums, 4 CSFs) from 5 patients were confirmed by CBA to be GABAAR-IgG positive. Patient IgGs were always reactive with α1β3 GABAAR subunits. One more patient was identified clinically after this validation study. Median age for the 6 patients at serologic diagnosis was 44 years (range, 1-71 years), and 4 of them were male. Among the 4 for whom clinical information was available (2 treated by the authors), all had encephalitis and antiepileptic drug refractory seizures. Three out of 4 patients treated with a combination of immunotherapies had good outcomes. The fourth, recognized to have an autoimmune cause late in the clinical course, had severe permanent neurologic sequelae and brain atrophy. Conclusions:Though not as common as NMDA-R encephalitis, GABAAR encephalitis generally has a characteristic clinical-radiologic presentation and is treatable, making accurate laboratory diagnosis critical.

Background and purpose: Paraneoplastic neurological autoimmunity is well described with small‐cell lung cancer, but information is limited for other neuroendocrine neoplasms (NENs). Methods: Adult patients with histopathologically confirmed non‐pulmonary NENs, neurological autoimmunity within 5 years of NEN diagnosis, and neural antibody testing performed at the Mayo Clinic Neuroimmunology Laboratory (January 2008 to March 2023) were retrospectively identified. Control sera were available from patients with NENs without neurological autoimmunity (116). Results: Thirty‐four patients were identified (median age 68 years, range 31–87). The most common primary tumor sites were pancreas (nine), skin (Merkel cell, eight), small bowel/duodenum (seven), and unknown (seven). Five patients received immune checkpoint inhibitor (ICI) therapy before symptom onset; symptoms preceded cancer diagnosis in 62.1% of non‐ICI‐treated patients. The most frequent neurological phenotypes (non‐ICI‐treated) were movement disorders (12; cerebellar ataxia in 10), dysautonomia (six), peripheral neuropathy (eight), encephalitis (four), and neuromuscular junction disorders (four). Neural antibodies were detected in 55.9% of patients studied (most common specificities: P/Q‐type voltage‐gated calcium channel [seven], muscle‐type acetylcholine receptor [three], anti‐neuronal nuclear antibody type 1 [three], and neuronal intermediate filaments [two]), but in only 6.9% of controls. Amongst patients receiving cancer or immunosuppressive therapy, 51.6% had partial or complete recovery. Outcomes were unfavorable in 48.3% (non‐ICI‐treated) and neural autoantibody positivity was associated with poor neurological outcome. Discussion: Neurological autoimmunity associated with non‐pulmonary NENs is often multifocal and can be treatment responsive, underscoring the importance of rapid recognition and early treatment. [ABSTRACT FROM AUTHOR]

Neuromyelitis optica (NMO) is a severe inflammatory autoimmune CNS disorder triggered by binding of an IgG autoantibody to the aquaporin 4 (AQP4) water channel on astrocytes. Activation of cytolytic complement has been implicated as the major effector of tissue destruction that secondarily involves myelin. We investigated early precytolytic events in the evolving pathophysiology of NMO in mice by continuously infusing IgG (NMO patient serum-derived or AQP4-specific mouse monoclonal), without exogenous complement, into the spinal subarachnoid space. Motor impairment and sublytic NMO-compatible immunopathology were IgG dose dependent, AQP4 dependent, and, unexpectedly, microglia dependent. In vivo spinal cord imaging revealed a striking physical interaction between microglia and astrocytes that required signaling from astrocytes by the C3a fragment of their upregulated complement C3 protein. Astrocytes remained viable but lost AQP4. Previously unappreciated crosstalk between astrocytes and microglia involving early-activated CNS-intrinsic complement components and microglial C3a receptor signaling appears to be a critical driver of the precytolytic phase in the evolving NMO lesion, including initial motor impairment. Our results indicate that microglia merit consideration as a potential target for NMO therapeutic intervention., Introduction Neuromyelitis optica (NMO) is an inflammatory autoimmune disorder of the central nervous system (CNS) with secondary myelin loss. It disproportionately affects women and non-White populations, typically presents as optic [...]

Objective: This study was undertaken to investigate factors associated with aquaporin‐4 (AQP4)‐IgG serostatus change using a large serological database. Methods: This retrospective study utilizes Mayo Clinic Neuroimmunology Laboratory data from 2007 to 2021. We included all patients with ≥2 AQP4‐IgG tests (by cell‐based assay). The frequency and clinical factors associated with serostatus change were evaluated. Multivariable logistic regression analysis examined whether age, sex, or initial titer was associated with serostatus change. Results: There were 933 patients who had ≥2 AQP4‐IgG tests with an initial positive result. Of those, 830 (89%) remained seropositive and 103 (11%) seroreverted to negative. Median interval to seroreversion was 1.2 years (interquartile range [IQR] = 0.4–3.5). Of those with sustained seropositivity, titers were stable in 92%. Seroreversion was associated with age ≤ 20 years (odds ratio [OR] = 2.25; 95% confidence interval [CI] = 1.09–4.63; p = 0.028) and low initial titer of ≤1:100 (OR = 11.44, 95% CI = 3.17–41.26, p < 0.001), and 5 had clinical attacks despite seroreversion. Among 62 retested after seroreversion, 50% returned to seropositive (median = 224 days, IQR = 160–371). An initial negative AQP4‐IgG test occurred in 9,308 patients. Of those, 99% remained seronegative and 53 (0.3%) seroconverted at a median interval of 0.76 years (IQR = 0.37–1.68). Interpretation: AQP4‐IgG seropositivity usually persists over time with little change in titer. Seroreversion to negative is uncommon (11%) and associated with lower titers and younger age. Seroreversion was often transient, and attacks occasionally occurred despite prior seroreversion, suggesting it may not reliably reflect disease activity. Seroconversion to positive is rare (<1%), limiting the utility of repeat testing in seronegative patients unless clinical suspicion is high. ANN NEUROL 2023;94:727–735 [ABSTRACT FROM AUTHOR]

Neuromyelitis optica (NMO) is an inflammatory demyelinating disease that selectively affects optic nerves and spinal cord. It is considered a severe variant of multiple sclerosis (MS), and frequently is misdiagnosed as MS, but prognosis and optimal treatments differ. A serum immunoglobulin G autoantibody (NMO-IgG) serves as a specific marker for NMO. Here we show that NMO-IgG binds selectively to the aquaporin-4 water channel, a component of the dystroglycan protein complex located in astrocytic foot processes at the blood-brain barrier. NMO may represent the first example of a novel class of autoimmune channelopathy.