Mechanisms of autoimmune encephalitis.

PURPOSE OF REVIEW: To provide an overview of the pathogenic mechanisms involved in autoimmune encephalitides mediated by antibodies against neuronal surface antigens, with a focus on NMDAR and LGI1 encephalitis. RECENT FINDINGS: In antibody-mediated encephalitides, binding of IgG antibodies to neuronal surface antigens results in different pathogenic effects depending on the type of antibody, IgG subclass and epitope specificity. NMDAR IgG1 antibodies cause crosslinking and internalization of the target, synaptic and brain circuitry alterations, as well as alterations of NMDAR expressing oligodendrocytes, suggesting a link with white matter lesions observed in MRI studies. LGI1 IgG4 antibodies, instead, induce neuronal dysfunction by disrupting the interaction with cognate proteins and altering AMPAR-mediated signaling. In-vitro findings have been corroborated by memory and behavioral changes in animal models obtained by passive transfer of patients' antibodies or active immunization. These models have been fundamental to identify targets for innovative therapeutic strategies, aimed at counteracting or preventing antibody effects, such as the use of soluble ephrin-B2, NMDAR modulators (e.g., pregnenolone, SGE-301) or chimeric autoantibody receptor T cells (CAART) in models of NMDAR encephalitis. SUMMARY: A deep understanding of the pathogenic mechanisms underlying antibody-mediated encephalitides is crucial for the development of new therapeutic approaches targeting brain autoimmunity.

A score that predicts aquaporin-4 IgG positivity in patients with longitudinally extensive transverse myelitis.

BACKGROUND AND PURPOSE: Longitudinally extensive transverse myelitis (LETM) associated with aquaporin-4 autoantibodies (AQP4-IgG) can cause severe disability. Early diagnosis and prompt treatment are critical to prevent relapses. A novel score is described based on clinical and neuroimaging characteristics that predicts AQP4-IgG positivity in patients with LETM. METHODS: Patients were enrolled both retrospectively and prospectively from multiple Italian centers. Clinical and neuroimaging characteristics of AQP4-IgG positive and negative patients were compared through univariate and multivariate analysis. RESULTS: Sixty-six patients were included. Twenty-seven (41%) were AQP4-IgG positive and median age at onset was 45.5 years (range 19-81, interquartile range 24). Female sex (odds ratio [OR] 17.9, 95% confidence interval [CI] 2.6-381.9; p = 0.014), tonic spasms (OR 45.6, 95% CI 3.1-2197; p = 0.017) and lesion hypointensity on T1-weighted images (OR 52.9, 95% CI 6.8-1375; p = 0.002) were independently associated with AQP4-IgG positivity. The AQP4-IgG positivity in myelitis (AIM) score predicted AQP4-IgG positivity with 85% sensitivity and 95% specificity. Positive and negative likelihood ratios were 16.6 and 0.2 respectively. The inter-rater and intra-rater agreement in the score application were both excellent. CONCLUSIONS: The AIM score predicts AQP4-IgG positivity with good sensitivity and specificity in patients with a first episode of LETM. The score may assist clinicians in early diagnosis and treatment of AQP4-IgG positive LETM.

Clinical features and outcome of patients with autoimmune cerebellar ataxia evaluated with the Scale for the Assessment and Rating of Ataxia.

BACKGROUND AND PURPOSE: This study was undertaken to assess the long-term outcome of patients with paraneoplastic and non paraneoplastic autoimmune cerebellar ataxia (ACA) using the Scale for the Assessment and Rating of Ataxia (SARA). METHODS: Patients with subacute cerebellar ataxia admitted to our institution between September 2012 and April 2020 were prospectively recruited. Serum and/or cerebrospinal fluid was tested for neural autoantibodies by indirect immunofluorescence on mouse brain, cell-based assays, and radioimmunoassay. SARA and modified Rankin Scale (mRS) score were employed to assess patients' outcome. RESULTS: Fifty-five patients were recruited, of whom 23 (42%) met the criteria for cerebellar ataxia of autoimmune etiology. Neural autoantibodies were detected in 22 of 23 patients (Yo-immunoglobulin G [IgG], n = 6; glutamic acid decarboxylase 65-IgG, n = 3; metabotropic glutamate receptor 1-IgG, n = 2; voltage-gated calcium channel P/Q type-IgG, n = 2; Hu-IgG, n = 1; glial fibrillary acidic protein-IgG, n = 1; IgG-binding unclassified antigens, n = 7). Thirteen patients were diagnosed with paraneoplastic cerebellar syndrome (PCS) and 10 with idiopathic ACA. All patients received immunotherapy. Median SARA score was higher in the PCS group at all time points (p = 0.0002), while it decreased significantly within the ACA group (p = 0.049) after immunotherapy. Patients with good outcome (mRS ≤ 2) had less neurological disability (SARA < 15) at disease nadir (p = 0.039) and presented less frequently with paraneoplastic neurological syndrome (p = 0.0028). The univariate linear regression model revealed a good correlation between mRS and SARA score both at disease onset (p < 0.0001) and at last follow-up (p < 0.0001). SARA score < 11 identified patients with good outcome. CONCLUSIONS: Patients with idiopathic ACA significantly improved after immunotherapy. SARA score accurately reflects patients' clinical status and may be a suitable outcome measure for patients with ACA.

Unprotected stroke management in an undiagnosed case of Severe Acute Respiratory Syndrome Coronavirus 2 infection.

Coronavirus disease 19 (COVID-19) is an emerging infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In this scenario, managing acute medical conditions, such as stroke, requires a timely treatment together with proper strategies that minimize the risk of infection spreading to health care workers and other patients. We report the case of a 79-year-old woman, who was admitted for a wake-up stroke due to occlusion of the left middle cerebral artery. She was treated outside the COVID-19-dedicated track of the hospital because she had no concomitant signs or symptoms suggestive of SARS-CoV-2 infection nor recent contact with other infected individuals. Post-mortem nasal and pharyngeal swab was positive for SARS-CoV-2 infection. We propose that hyperacute stroke patients should be tested for SARS-CoV-2 infection at admission and then managed as having COVID-19 until cleared by a negative result. We are aware that such measure results in some delay of the acute treatment of stroke, which could be minimal using well-exercised containment protocols.

Isolated Memory Loss in Anti-NMDAR Encephalitis.

BACKGROUND AND OBJECTIVES: To report a case of anti-NMDAR encephalitis presenting with isolated memory dysfunction. METHODS: A 29-year-old woman was admitted to the Neurology Department referring memory impairment with a subacute onset. The initial assessment included EEG, neuropsychological tests, and brain MRI. Serum and CSF samples were collected for immunologic studies. The diagnostic evaluation was completed with a total body PET scan. RESULTS: Patient's neurologic examination was unremarkable apart from an episodic memory deficit, confirmed by neuropsychological examination. The EEG revealed epileptiform discharges in the temporal lobes, whereas brain MRI showed bilateral temporal lobes hyperintense lesions on fluid-attenuated inversion recovery images and T2-weighted images. NMDAR-IgG was detected in the patient's serum and CSF by cell-based assay confirming the diagnosis of definite anti-NMDAR encephalitis. The total body PET showed only a slight hypometabolism in the right temporal cortex and in the cerebellar hemispheres. After a course of IV immunoglobulin and corticosteroid therapy, a marked improvement of the memory deficit was observed. DISCUSSION: This case shows that anti-NMDAR encephalitis can present with isolated memory loss. Neural antibody testing in these patients could play a pivotal role in early diagnosis and prompt treatment.

Real-world application of the updated diagnostic criteria for paraneoplastic neurological syndromes.

Following recent discoveries, diagnostic criteria for paraneoplastic neurological syndromes (PNS) have been recently updated. However, how the criteria impact PNS diagnosis is still unclear. We retrospectively applied the previously existing 2004 criteria (2004-c) and the updated 2021 diagnostic criteria (2021-c) to 74 patients with suspect PNS. The 2021 criteria were highly sensitive (88%) and specific (80%). There was good concordance between the definite PNS group (2004-c) and the definite plus probable PNS group (2021-c). The inter-rater reliability for the 2021-c was excellent. The application of the 2021 criteria improves the diagnosis of patients with PNS.

MOG autoimmunity mimicking CLIPPERS syndrome: Case report and literature review.

Chronic lymphocytic inflammation with pontine perivascular enhancement responsive to steroids (CLIPPERS) is an inflammatory syndrome characterized by the predominant involvement of the pons, the cerebellum and the spinal cord with a distinct corticosteroid responsiveness. To date, several cases of neurological disorders with a CLIPPERS-like phenotype have been described, including patients with Immunoglobulin G (IgG) antibodies binding to myelin oligodendrocyte glycoprotein (MOG). We herein report the case of a man with myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) fulfilling the diagnostic criteria for probable CLIPPERS and a literature review of CLIPPERS-mimicking patients with MOG-IgG.

Neuromyelitis optica, aquaporin-4 antibodies, and neuroendocrine disorders.

Neuromyelitis optica (NMO) is an autoimmune disorder of the central nervous system that preferentially affects the optic nerve and the spinal cord. In around 80% of NMO patients, autoantibodies binding to aquaporin-4 (AQP4) are detected. AQP4-IgG unifies a spectrum of disorders (NMOSD) that include not only optic neuritis, longitudinally extensive transverse myelitis but also syndromes caused by lesion of the diencephalic region and the circumventricular organs (CVOs). The distinctive immunopathological characteristics of NMOSD lesions, occurring in regions where AQP4 is highly expressed, supports a central role for AQP4-IgG in disease pathogenesis. AQP4 expression is concentrated in CVOs and in the hypothalamus, mainly in the dorsal hypothalamic area, dorsomedial hypothalamic nucleus and suprachiasmatic nucleus. Several neuroendocrine disorders caused by inflammatory lesions involving the diencephalic region have been described in patients with NMOSD, including syndrome of inappropriate antidiuresis, sleep disorders, and other endocrinopathies caused by hypothalamic injury. Focus of this chapter is the involvement of hypothalamus and CVOs in AQP4 autoimmunity.

Assessing the role of a tissue-based assay in the diagnostic algorithm of autoimmune encephalitis.

Tissue-based assay (TBA) is a widely-used method to detect neural autoantibodies, but the diagnostic accuracy for autoimmune encephalitis (AE) has not yet been adequately measured. We retrospectively evaluated the sensitivity and specificity of an indirect immunofluorescence TBA (IIF-TBA) in 159 patients with suspected AE. Serum and cerebrospinal fluid (CSF) specimens were collected and tested from December 2012 to September 2020. In the paired sample analysis, serum testing showed higher sensitivity than CSF, while the latter had higher specificity. Based on these results, we clarify the advantages of using a TBA as the principal screening method for patients with suspected AE.

Clinical and neuroimaging characteristics of MOG autoimmunity in children with acquired demyelinating syndromes.

Background Myelin oligodendrocyte glycoprotein antibodies (MOG-IgG) have been recently reevaluated as a biomarker of acquired demyelinating syndromes (ADS) of the central nervous system (CNS). Here, we describe the clinical and neuroimaging features, and the long-term outcome of children with ADS of the CNS associated with MOG-IgG. Methods All patients underwent brain and spinal cord magnetic resonance imaging (MRI), lumbar puncture for cerebrospinal fluid (CSF) analysis and MOG-IgG and aquaporin-4 IgG (AQP4-IgG) testing. Results Forty-eight pediatric patients were recruited. MOG-IgG were detected in 11/48 (25%) patients with the following clinical presentations: encephalomyelitis (EM), 8/11 (73%); optic neuritis (ON), 2/11 (18%); transverse myelitis (TM), 1/11 (9%). Patients negative for MOG-IgG were diagnosed with Multiple Sclerosis (MS) (n=15), EM (n=7), ON (n=7), neuromyelitis optica spectrum disorders (NMOSD) (n=5), TM (n=2) and encephalitis (n=1). MOG-IgG positive patients were younger at disease onset and they more frequently experienced encephalopathy and epileptic seizures compared with negative patients. EM and inflammatory lesions involving optic nerves on MRI imaging were more frequent in MOG-IgG positive patients. None of the patients with MOG-IgG became persistently seronegative during the follow-up, although a decrease in MOG-IgG titer was observed. Patients with MOG-IgG showed a good response to therapy and only two patients presented relapses during follow-up. Conclusion This study supports the distinction of MOG autoimmune oligodendrocytopathy as a unique disease entity, with clinical features different from those of MS and AQP4-IgG-positive NMOSD.

Reversal of long term potentiation-like plasticity in primary motor cortex in patients with progressive supranuclear palsy.

OBJECTIVE: Abnormal primary motor cortex plasticity might be involved in the pathophysiology of progressive supranuclear palsy. In the present study we aimed to investigate possible abnormalities of depotentiation, a mechanism involved in plasticity regulation, in this condition. METHODS: Primary motor cortex excitability, investigated with single and paired-pulse transcranial magnetic stimulation, as well as long-term potentiation-like plasticity and its reversibility, were studied using theta burst stimulation in 15 patients with progressive supranuclear palsy and 11 healthy controls. Participants underwent two sessions using (1) the intermittent theta-burst stimulation (potentiation protocol) and (2) intermittent theta-burst stimulation combined with a depotentiation protocol (a short continuous theta-burst stimulation). RESULTS: Patients with PSP had higher corticospinal excitability and lower intracortical inhibition than healthy controls. Intermittent theta-burst stimulation elicited an abnormally increased long term potentiation-like effect in patients in comparison to healthy subjects. However, the depotentiation protocol was able to reverse the effects intermittent theta-burst stimulation on motor cortex excitability both in patients and in healthy controls. CONCLUSIONS: Altered primary motor cortex plasticity in patients with PSP does not reflect an abnormality of depotentiation. SIGNIFICANCE: This study provides information for a deeper understanding of the possible pathophysiological mechanisms underlying the altered M1 plasticity in PSP.

Vasculitic Ulcers.

Vasculitic ulcers are an emerging problem in wound care that needs to be well defined and adequately approached by caregivers. Cutaneous vasculitis includes several inflammatory disorders that compromise microvessels and specifically the cutaneous vascular system: arterioles, capillaries, postcapillary venules. The pathogenetic role of circulating immunocomplexes and autoantibodies (antineutrophil antibodies) in these diseases has been widely demonstrated in animal models and in humans. Vasculitis can be limited to the skin or represent the cutaneous signs in case of systemic vasculitis with visceral involvement. The injury of cutaneous microvessels may result in impairment of blood flow and consequent focal ischemia and formation of skin ulcers. The ulcers are often multiple and localized on the lower leg and foot where the microcirculatory anatomy and rheologic dynamics are predisposing factors. Approximately 3% to 5% of skin ulcers may be caused by a vasculitic disorder.