GAD antibodies associated neurological disorders: incidence and phenotype distribution among neurological inflammatory diseases

The IVIG treatment response in autoimmune polyendocrine syndromes type 2 with anti-GAD65 antibody-associated stiff person syndrome: a case report and literature review

Autoimmune polyendocrine syndromes (APS) is a rare group of disorders caused by impaired function of multiple endocrine glands due to disruption of immune tolerance. Of which, type 2 (APS-2) is the most common. Glutamic acid decarboxylase (GAD) is the rate-limiting enzyme for the synthesis of gamma-aminobutyric acid (GABA). Anti-GAD antibodies are associated with various neurological disorders, including stiff person syndrome (SPS). SPS is characterized by axial muscle stiffness, rigidity, and intermittent painful muscle spasms, with a prevalence of one to two in a million, making it an extremely rare neurological disorder. The comorbidity of APS-2 with SPS is even rarer. Most practicing neurologists encounter only one or two cases of APS-2 combined with anti-GAD65 antibody-associated SPS in their careers, resulting in underdiagnosis and undertreatment, leading to severe disability and suffering. This case report describes a young male who initially exhibited hair loss, vitiligo, and previously unreported eosinophilia. Before his diagnosis, he was admitted multiple times, with symptoms improving following the addition of intravenous immunoglobulin (IVIG) therapy to a poor treatment regimen. This paper aims to increase physicians' awareness of this condition, enhancing the likelihood of early diagnosis and treatment.

Pathophysiological Effects of Autoantibodies in Autoimmune Encephalitides

The heterogeneity of autoantibody targets in autoimmune encephalitides presents a challenge for understanding cellular and humoral pathophysiology, and the development of new treatment strategies. Thus, current treatment aims at autoantibody removal and immunosuppression, and is primarily based on data generated from other autoimmune neurological diseases and expert consensus. There are many subtypes of autoimmune encephalitides, which now entails both diseases with autoantibodies targeting extracellular antigens and classical paraneoplastic syndromes with autoantibodies targeting intracellular antigens. Here, we review the current knowledge of molecular and cellular effects of autoantibodies associated with autoimmune encephalitis, and evaluate the evidence behind the proposed pathophysiological mechanisms of autoantibodies in autoimmune encephalitis.

Psychiatric Symptoms in Stiff-Person Syndrome: A Systematic Review and a Report of Two Cases

BACKGROUND

The clinical spectrum of stiff-person syndrome (SPS) encompasses a wide range of signs including psychiatric symptoms (PS).

OBJECTIVE

Our objective was to provide an overview of the spectrum of PS in SPS through a systematic literature search and 2 illustrative case reports.

METHODS

We reported 2 anti-glutamic acid decarboxylase-positive SPS cases that presented with phobic disorder, and we performed a systematic review by following the 2020 Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Articles published in PubMed, MEDLINE on Ovid, Embase, and via a manual search before October 20, 2020, were selected by 2 independent reviewers. Original studies, case reports, editorials, commentaries, and letters to the editor reporting cases of SPS with PS were all included. Conference abstracts, reviews and book chapters, unavailable articles, and those not reporting SPS cases or PS were excluded. Quantitative summary data were calculated.

RESULTS

In addition to our 2 cases, we identified 237 cases of SPS with PS from 74 additional included publications totaling 239 patients. Anxiety (56%) and depression (45%) were the most common PS in SPS. Mean diagnostic delay was 4.7 years. Among the 3 SPS phenotypes, the classic form was predominant (77%), followed by stiff-limb syndrome (13%) and progressive encephalomyelitis with rigidity and myoclonus (10%). The most frequent etiology of SPS with PS was autoimmune (90%), followed by cryptogenic (7%) and paraneoplastic forms (7%). These patients were mainly treated with immune-mediated therapies and GABAergic drugs.

CONCLUSIONS

Our review revealed that the most common PS of SPS are anxiety and depression occurring mostly in autoimmune and classic forms, allowing a clearer understanding of this entity, which may lead to earlier diagnosis and better outcome.

A Case of Anti-glutamic Acid Decarboxylase-65 Antibody Positive Stiff Person Syndrome Presenting Initially as Acute Peripheral Vestibulopathy, Leading to Delayed Diagnosis After Multiple Hospitalizations

Stiff person syndrome (SPS), with a prevalence of one to two per million, is an extremely rare neurological condition that is characterized by axial muscle stiffness and rigidity along with intermittent painful muscle spasms. It is often associated with psychiatric co-morbidities such as anxiety and depression. The pathophysiology, although poorly understood, is widely believed to be autoimmune in nature due to the association of anti-glutamic acid decarboxylase-65 (anti-GAD 65) antibodies with this condition. There is also a paraneoplastic variant that is more commonly associated with anti-ampiphysin antibodies. It occurs most commonly in patients with breast cancer followed by colon cancer. Most of the practising neurologists encounter just one or two cases of SPS in their entire careers, hence this condition remains underdiagnosed, leading to significant disability and distress to the patient. In this case report we describe a postmenopausal female who presented initially with symptoms of vertigo and dizziness and was hospitalized multiple times before the diagnosis was reached. Through this article, we attempt to increase awareness about this condition among practising physicians so as to increase the likelihood of earlier diagnosis and treatment. 

An evolving redefinition of autoimmune encephalitis

Autoimmune encephalitis encompasses a wide variety of protean pathologic processes associated with the presence of antibodies against neuronal intracellular proteins, synaptic receptors, ion channels and/or neuronal surface proteins. This type of encephalitis can also involve children with complex patterns of seizures and unexpected behavioural changes, which jeopardize their prompt recognition and treatment. Many epidemiological studies have shown that numerous immune-based forms of encephalitis can be encountered, almost surpassing the rate of postinfectious encephalitides. However, the overall exact prevalence of autoimmune encephalopathies remains underestimated, and the definition of diagnostic algorithms results muddled. The spectrum of neuropsychiatric manifestations in the pediatric population with autoimmune encephalitis is less clear than in adults, but the integration of clinical, immunological, electrophysiological and neuroradiological data is essential for a general approach to patients. In this review we report the most relevant data about both immunologic and clinical characteristics of the main autoimmune encephalitides recognized so far, with the aim of assisting clinicians in the differential diagnosis and favouring an early effective treatment. Correlations between phenotype and autoantibodies involved in the neurological damage of autoimmune encephalitis are largely unknown in the first years of life, because of the relatively small number of pediatric patients adequately studied. Future multicenter collaborative studies are needed to improve the diagnostic approach and tailor personalized therapies in the long-term.

Recent Advances and Review on Treatment of Stiff Person Syndrome in Adults and Pediatric Patients

Stiff Person Syndrome (SPS) is one of the rarest autoimmune neurological disorders, which is mostly reported in women. It is characterised by fluctuating muscle rigidity and spasms. There are many variants of SPS, these include the classical SPS, Stiff Leg Syndrome (SLS), paraneoplastic variant, gait ataxia, dysarthria, and abnormal eye movements. Studies have shown that the paraneoplastic variant of SPS is more common in patients with breast cancer who harbour amphiphysin antibodies, followed by colon cancer, lung cancer, Hodgkin's disease, and malignant thymoma. 

Currently, the treatment for SPS revolves around improving the quality of life by reducing the symptoms as far as possible with the use of GABAergic agonists, such as diazepam or other benzodiazepines, steroids, plasmapheresis, and intravenous immunoglobulin (IVIG). There have been random clinical trials with Rituximab, but nothing concrete has been suggested. A treatment approach with standard drugs and cognitive behavioral therapy (CBT) seems to be promising.

Disease-specific monoclonal antibodies targeting glutamate decarboxylase impair GABAergic neurotransmission and affect motor learning and behavioral functions

Autoantibodies to the smaller isoform of glutamate decarboxylase (GAD) can be found in patients with type 1 diabetes and a number of neurological disorders, including stiff-person syndrome, cerebellar ataxia and limbic encephalitis. The detection of disease-specific autoantibody epitopes led to the hypothesis that distinct GAD autoantibodies may elicit specific neurological phenotypes. We explored the in vitro/in vivo effects of well-characterized monoclonal GAD antibodies. We found that GAD autoantibodies present in patients with stiff person syndrome (n = 7) and cerebellar ataxia (n = 15) recognized an epitope distinct from that recognized by GAD autoantibodies present in patients with type 1 diabetes mellitus (n = 10) or limbic encephalitis (n = 4). We demonstrated that the administration of a monoclonal GAD antibody representing this epitope specificity; (1) disrupted in vitro the association of GAD with γ-Aminobutyric acid containing synaptic vesicles; (2) depressed the inhibitory synaptic transmission in cerebellar slices with a gradual time course and a lasting suppressive effect; (3) significantly decreased conditioned eyelid responses evoked in mice, with no modification of learning curves in the classical eyeblink-conditioning task; (4) markedly impaired the facilitatory effect exerted by the premotor cortex over the motor cortex in a paired-pulse stimulation paradigm; and (5) induced decreased exploratory behavior and impaired locomotor function in rats. These findings support the specific targeting of GAD by its autoantibodies in the pathogenesis of stiff-person syndrome and cerebellar ataxia. Therapies of these disorders based on selective removal of such GAD antibodies could be envisioned.

Stiff person-syndrome IgG affects presynaptic GABAergic release mechanisms

The majority of patients with stiff person-syndrome (SPS) are characterized by autoantibodies to glutamate decarboxylase 65 (GAD65). In previous passive-transfer studies, SPS immunoglobulin G (IgG) induced SPS core symptoms. We here provide evidence that SPS-IgG causes a higher frequency of spontaneous vesicle fusions. Sustained GABAergic transmission and presynaptic GABAergic vesicle pool size remained unchanged. Since these findings cannot be attributed to anti-GAD65 autoantibodies alone, we propose that additional autoantibodies with so far undefined antigen specificity might affect presynaptic release mechanisms.

Immunotherapy-responsive limbic encephalitis with antibodies to glutamic acid decarboxylase

Glutamic acid decarboxylase (GAD) has been recently identified as a target of humoral autoimmunity in a small subgroup of patients with non-paraneoplastic limbic encephalitis (NPLE). We present a patient with NPLE and positive anti-GAD antibodies who showed significant improvement after long-term immunotherapy. A 48-year old female was admitted with a two-year history of anterograde amnesia and seizures. Brain MRI revealed bilateral lesions of medial temporal lobes. Screening for anti-neuronal antibodies showed high anti-GAD titers in both serum and cerebrospinal fluid (CSF) with strong evidence of intrathecal production. The patient received treatment with prednisolone and long-term plasma exchange. During a 12-month follow-up, she exhibited complete seizure remission and an improvement in memory and visuo-spatial skills. Anti-GAD antibodies may serve as a useful marker to identify a subset of NPLE patients that respond to immunoregulatory treatment.

Current approaches to the treatment of paraneoplastic encephalitis

Paraneoplastic neurological syndromes (PNSs) cover a wide range of diseases and involve both the central nervous system (CNS) and peripheral nervous system. Paraneoplastic encephalitis comprises several diseases such as paraneoplastic cerebellar degeneration (PCD), limbic encephalitis (LE), paraneoplastic encephalomyelitis (PEM), brainstem encephalitis, opsomyoclonus syndrome, in addition to other even less frequently occurring entities. LE was the first historically identified CNS PNS, and similarities between other temporal lobe diseases such as herpes encephalitis have been elucidated. In the past few decades several autoantibodies have been described in association with LE. These encompass the classical 'onconeuronal' antibodies (abs) such as Hu, Yo, Ri and others, and now additionally abs towards either ion channels or surface antigens. The clinical core findings in LE are various mental changes such as amnesia or confusion, often associated with seizures. Careful characterization of psychiatric manifestations and/or associated neurological signs can help to characterize the syndrome and type of ab. The treatment options in LE depend on the aetiology. In LE caused by onconeuronal abs, the treatment options are poor. In two types of abs associated with LE, abs against ion channels and surface antigens (e.g. NMDA), immunomodulatory treatments seem effective, making these types of LE treatable conditions. However, LE can also occur without being associated with cancer, in which case only immunomodulation is required. Despite effective treatments, some patients' residual deficits remain, and recurrences have also been described.