Intrathecal-specific glutamic acid decarboxylase antibodies at low titers in autoimmune neurological disorders

Consensus Paper: Latent Autoimmune Cerebellar Ataxia (LACA)

Immune-mediated cerebellar ataxias (IMCAs) have diverse etiologies. Patients with IMCAs develop cerebellar symptoms, characterized mainly by gait ataxia, showing an acute or subacute clinical course. We present a novel concept of latent autoimmune cerebellar ataxia (LACA), analogous to latent autoimmune diabetes in adults (LADA). LADA is a slowly progressive form of autoimmune diabetes where patients are often initially diagnosed with type 2 diabetes. The sole biomarker (serum anti-GAD antibody) is not always present or can fluctuate. However, the disease progresses to pancreatic beta-cell failure and insulin dependency within about 5 years. Due to the unclear autoimmune profile, clinicians often struggle to reach an early diagnosis during the period when insulin production is not severely compromised. LACA is also characterized by a slowly progressive course, lack of obvious autoimmune background, and difficulties in reaching a diagnosis in the absence of clear markers for IMCAs. The authors discuss two aspects of LACA: (1) the not manifestly evident autoimmunity and (2) the prodromal stage of IMCA's characterized by a period of partial neuronal dysfunction where non-specific symptoms may occur. In order to achieve an early intervention and prevent cell death in the cerebellum, identification of the time-window before irreversible neuronal loss is critical. LACA occurs during this time-window when possible preservation of neural plasticity exists. Efforts should be devoted to the early identification of biological, neurophysiological, neuropsychological, morphological (brain morphometry), and multimodal biomarkers allowing early diagnosis and therapeutic intervention and to avoid irreversible neuronal loss.

Neurological Manifestations of Glutamic Acid Decarboxylase Autoimmunity in Indian Patients

Objective

To study the neurological manifestations of glutamic acid decarboxylase (GAD 65) autoimmunity in Indian patients.

Methods

Retrospective study conducted in a tertiary care referral hospital in South India. Patients who tested positive for GAD 65 antibodies from February 2013 to July 2019 were included.

Results

We identified 922 patients who underwent GAD 65 testing, of which 81 tested positive (8.78%) [mean age 55.42 years (SD 17.39, range 9-86 years, median age 57 years)]. Males (n = 47) outnumbered the females (n = 34). All the GAD values measured were <5000 IU/ml. There were 34 cases (42%) of atypical parkinsonism (16/34, 47% fulfilled the diagnostic criteria for autoimmune atypical parkinsonism) in our series forming the most common group with GAD 65 positivity, followed by autoimmune encephalitis (8 cases, 9.88%). Men were more affected with atypical parkinsonism (22/34; 64.70%), stiff person syndrome (2/3; 66.66%), and neuropathy (4/7; 57.1%) while women were more with autoimmune encephalitis (6/8; 75%). Eighteen (22.6%) had underlying autoimmunity (three had type 1 diabetes mellitus). Six (7.4%) had underlying neoplasm. Thirty-three out of 43 patients responded to immunotherapy (76.74%). Five had spontaneous improvement.

Conclusion

Glutamic acid decarboxylase65 antibody values were much lower in our study population. Male-dominant autoimmunity was seen unlike that in Western literature. The most striking was the high preponderance of atypical parkinsonism in GAD 65-positive patients. We also found that GAD 65 positivity is a useful marker for a positive response to immunotherapy in suspected autoimmune neurological syndromes irrespective of their titers.

Glutamic acid decarboxylase antibody-associated neurological syndromes: Clinical and antibody characteristics and therapy response

BACKGROUND

Antibodies against glutamic acid decarboxylase (GAD-abs) at high serum levels are associated with diverse autoimmune neurological syndromes (AINS), including cerebellar ataxia, epilepsy, limbic encephalitis and stiff-person syndrome. The impact of low serum GAD-ab levels in patients with suspected AINS remains controversial. Specific intrathecal GAD-ab synthesis may serve as a marker for GAD-ab-associated nervous system autoimmunity. We present characteristics of a multicentric patient cohort with suspected AINS associated with GAD antibodies (SAINS-GAD+) and explore the relevance of serum GAD-ab levels and intrathecal GAD-ab synthesis.

METHODS

All patients with SAINS-GAD+ included in the registry of the German Network for Research on Autoimmune Encephalitis (GENERATE) from 2011 to 2019 were analyzed. High serum GAD-ab levels were defined as RIA>2000 U/mL, ELISA>1000 U/mL, or as a positive staining pattern on cell-based assays.

RESULTS

One-hundred-one patients were analyzed. In descending order they presented with epilepsy/limbic encephalitis (39%), cerebellar ataxia (28%), stiff person syndrome (22%), and overlap syndrome (12%). Immunotherapy was administered in 89% of cases with improvements in 46%. 35% of SAINS-GAD+ patients had low GAD-ab serum levels. Notably, unmatched oligoclonal bands in CSF but not in serum were more frequent in patients with low GAD-ab serum levels. GAD-ab-levels (high/low) and intrathecal GAD-ab synthesis (present or not) did not impact clinical characteristics and outcome.

CONCLUSIONS

Overall, immunotherapy in SAINS-GAD+ was moderately effective. Serum GAD-ab levels and the absence or presence of intrathecal GAD-ab synthesis did not predict clinical characteristics or outcomes in SAINS-GAD+. The detection of unmatched oligoclonal bands might outweigh low GAD-ab serum levels.

Neuroimaging Pearls from the MDS Congress Video Challenge. Part 2: Acquired Disorders

The MDS Video Challenge continues to be the one of most widely attended sessions at the International Congress. Although the primary focus of this event is the presentation of complex and challenging cases through videos, a number of cases over the years have also presented an unusual or important neuroimaging finding related to the case. We reviewed the previous Video Challenge cases and present here a selection of those cases which incorporated such imaging findings. We have compiled these "imaging pearls" into two anthologies. The first focuses on pearls where the underlying diagnosis was a genetic condition. This second anthology focuses on imaging pearls in cases where the underlying condition was acquired. For each case we present brief clinical details along with neuroimaging findings, the characteristic imaging findings of that disorder and, finally, the differential diagnosis for the imaging findings seen.

Determinants of cognition in autoimmune limbic encephalitis-A retrospective cohort study

Autoimmune limbic encephalitis (ALE) is the most common type of autoimmune encephalitis (AIE). Subacute memory disturbance, temporal lobe seizures, and psychiatric symptoms are clinical hallmarks of the disease. However, little is known on the factors contributing to cognitive functioning in ALE. Hence, we here investigate major determinants of cognitive functioning in ALE. In a retrospective analysis of 102 patients with ALE, we first compared verbal learning capacity, nonverbal learning capacity, and attentional and executive functioning by absence or presence of different types of neural autoantibodies (AABs). Subsequently we established three linear regression models including 63, 38, and 61 patients, respectively to investigate how cognitive functioning in these domains may depend on common markers of ALE such as intrathecal inflammation, blood-cerebrospinal fluid (CSF)-barrier function, mesiotemporal epileptiform discharges and slowing, determined by electroencephalography (EEG) and structural mesiotemporal changes, measured with magnetic resonance imaging (MRI). We also accounted for possible effects of cancer- and immunotherapy and other centrally effective medication. There was no effect of AAB status on cognitive functioning. Although the regression models could not predict verbal and nonverbal learning capacity, structural mesiotemporal neural network alterations on T2-/fluid attenuated inversion recovery (FLAIR)-signal-weighted MRI and mesiotemporal epileptiform discharges or slowing on EEG exerted a significant impact on memory functions. In contrast, the regression model significantly predicted attentional and executive functioning with CSF white blood cell count and centrally effective medication being significant determinants. In this cohort, cognitive functioning in ALE does not depend on the AAB status. Common markers of ALE cannot predict memory functioning that only partially depends on structural and functional alterations of mesiotemporal neural networks. Common markers of ALE significantly predict attentional and executive functioning that is significantly related to centrally effective medication and CSF white blood cell count, which may point toward inflammation affecting brain regions beyond the limbic system.

Atypical parkinsonism and intrathecal anti-glutamic acid decarboxylase antibodies - an unusual association: a case report

Background

Immunological causes of parkinsonism are very rare and usually characterized by early presentation, poor response to levodopa, and additional clinical features.

Case presentation

We describe a 58-year-old white man who presented with a 1-year history of gait disturbance with disequilibrium leading to falls. We report an association between parkinsonism and presence of anti-glutamic acid decarboxylase antibodies in his cerebrospinal fluid, discussing clinical presentation and follow-up.

Conclusions

Besides the possibility of a casual association, this case allows us to hypothesize an alternative pathophysiological mechanism of parkinsonism implying interference with glutamic acid decarboxylase and gamma-aminobutyric acid functions, eventually resulting in basal ganglia circuit dysregulation.

Nonparaneoplastic autoimmune cerebellar ataxias

PURPOSE OF REVIEW

The current review develops the clinical presentations of nonparaneoplastic autoimmune cerebellar ataxia (ACA) and analyzes the association with autoantibodies.

RECENT FINDINGS

Emerging evidence suggests that autoimmunity is involved in a significant proportion of sporadic ataxia cases. Moreover, numerous autoantibodies have recently been described in association with sporadic cerebellar ataxia, improving diagnosis and patient categorization.

SUMMARY

Nonparaneoplastic ACA encompasses postinfectious acute cerebellar ataxia, opsoclonus-myoclonus-ataxia syndrome, and pure cerebellar ataxia with or without autoantibodies. There is still confusion about how to diagnose and classify the patients, and retrospective data suggest that these very rare entities are in fact largely underrecognized. Numerous autoantibodies have been found associated with sporadic ataxia, improving diagnosis accuracy, and patient categorization. However, although anti-glutamate decarboxylase isotype 65 (GAD65), anti-contactin-associated protein 2 (CASPR2), and anti metabotropic glutamate receptor (mGluR1) antibodies are well recognized biomarkers, many other autoantibodies have been described in very small numbers of patients and their specificity is unknown. Efficient biomarkers for ACA are still lacking and in many cases the diagnosis has to rely on a body of converging evidence.

Bortezomib treatment for severe refractory anti-NMDA receptor encephalitis

OBJECTIVE

To evaluate the therapeutic potential of bortezomib, a proteasome inhibitor that target plasma cells, in order to revive stalled recovery in patients with anti-N-methyl-d-aspartate (NMDA) receptor encephalitis who remain bedridden even after aggressive immunotherapy.

METHODS

We consecutively enrolled patients with anti-NMDA receptor encephalitis who remained bedridden after first-line immunotherapy (steroids and intravenous immunoglobulin), second-line immunotherapy (rituximab), and tocilizumab treatment, and treated them with subcutaneous bortezomib. Clinical response, functional recovery, and changes in antibody titer in the serum and cerebrospinal fluid were measured.

RESULTS

Before the bortezomib treatment, the five patients with severe refractory anti-NMDA receptor encephalitis were in a vegetative state. During the 8 months of follow-up period, three patients improved to minimally conscious states within 2 months of bortezomib treatment, one failed to improve from a vegetative state. However, no patient achieved functional recovery as measured by the modified Rankin Scale score (mRS). Three patients advanced to a cyclophosphamide with bortezomib and dexamethasone regimen, which only resulted in additional adverse events, without mRS improvement. Among the four patients whose antibody titer was followed, two demonstrated a twofold decrease in the antibody titer in serum and/or cerebrospinal fluid after 2 cycles of bortezomib.

INTERPRETATION

Although there were some improvements in severe refractory patients, clinical response to bortezomib was limited and not clearly distinguishable from the natural course of the disease. The clinical benefit of bortezomib in recent studies requires further validation in different clinical settings.

Anti-Neuronal Autoantibodies in Both Drug Responsive and Resistant Focal Seizures with Unknown Cause

BACKGROUND

and Objective Autoimmunity is an emerging field of research in the etiology of different neurological disorders including epilepsy. We aimed to investigate the presence of neuronal autoantibodies in focal epilepsy with unknown cause and their clinical correlates in both drug-responsive and resistant patients.

METHOD

Between 2009 and 2010 94 patients were prospectively enrolled, had their antibodies tested and clinically followed." An additional 50 age- and gender-matched controls were also tested for antibodies. Age at examination, gender, age at onset, seizure frequency, risk factors, seizure precipitants, and type of seizures were noted. Plasma obtained from patients was frozen at -80°C and analysed for autoantibodies against VGKC-complex, VGCC, GAD, LGI1, CASPR2, NMDA, AMPA and GABAB receptors with immunocytochemistry and radioimmunoassay as required.

RESULTS

Thirteen (13.8%) patients, but none of the controls, had antibodies (p=0.003). Antibodies were directed against the uncharacterized components of VGKC-complex in 5 patients (5.3%), GAD in 4 patients (4.2%), NMDA-R in 1 patient (1%), AMPA-R in 1 patient (1%) and both GAD and VGKC-complex in 2 patients (2.1%). Prognosis of epilepsy, in subsequent follow-up, did not correlate to general presence of anti-neuronal antibodies with slightly more patients with antibodies epilepsy control than without (76.9% vs. 69.1%, not-statistically significant. Three patients with suspected active autoimmunity and epilepsy who were treated, showed a response to treatment with a reduction in the seizure frequency. Although most clinical features were identical between seropositive and seronegative patient groups, seropositive patients were more likely to have inflammatory/autoimmune disorders in their medical history.

DISCUSSION

In keeping with previous studies, we have shown anti-neuronal antibodies in a proportion of focal epilepsy patients. Although autoimmunity might merely occur as a bystander effect in many chronic neurological disorders, association of anti-neuronal antibodies with good response to immunotherapy and coexisting autoimmune disorders suggests that anti-neuronal autoimmunity might participate in seizure formation at least in a subgroup of focal epilepsy patients.

CONCLUSION

Immunity may play a role in some patients with unknown etiology regardless of prognosis and immunmodulatuar treatment may be helpful in seropositive group.

Advances in Autoimmune Epilepsy Associated with Antibodies, Their Potential Pathogenic Molecular Mechanisms, and Current Recommended Immunotherapies

In this comprehensive article, we present an overview of some most common autoimmune antibodies believed to be potentially pathogenic for autoimmune epilepsies and elaborate their pathogenic mode of action in molecular levels based on the existing knowledge. Findings of the studies of immunemodulatory treatments for epilepsy are also discussed, and guidelines for immunotherapy are sorted out. We aim to summarize the emerging understanding of different pathogenic mechanisms of autoantibodies and clinical immunotherapy regimens to open up therapeutic possibilities for future optimum therapy. We conclude that early diagnosis of autoimmune epilepsy is of great significance, as early immune treatments have useful disease-modifying effects on some epilepsies and can facilitate the recovery.