Epilepsy and cerebellar ataxia associated with anti-glutamic acid decarboxylase antibodies

Immunotherapy in a case of low titre GAD65 antibody-associated spectrum neurological disorders

We present a rare case of low titre GAD65 antibody-associated autoimmune encephalitis and status epilepticus in a young woman. She initially presented with left arm dystonic movements, contractures and status epilepticus. Due to the concern of autoimmune encephalitis and seizures, the patient received intravenous immunoglobulin empirically. After the detection of low serum GAD65 antibodies, the patient underwent immunomodulation therapy with significant improvement. This case demonstrated that in autoimmune encephalitis, it is important to monitor serum GAD65 antibodies levels and consider immunotherapy, despite mildly elevated serum levels. The patient's history of left arm dystonic movements without impaired awareness may have been due to limb dystonia, a presenting symptom of stiff person syndrome (SPS), despite SPS more commonly affecting axial muscles. This case further demonstrates that GAD65 antibody-related syndromes can manifest with different neurological phenotypes including co-occurrence of epilepsy with possible focal SPS despite low GAD65 antibodies titres.

Assessment of anti-GAD65-associated cerebellar ataxia with 18F-FDG cerebellar uptake: ROC analysis

OBJECTIVE

Anti-glutamic acid decarboxylase 65 (anti-GAD65)-associated neurological disorders include two major phenotypes, namely Stiff person syndrome (SPS) and cerebellar ataxia (CA). Considering the potential for better outcomes with prompt immunotherapy, early detection of CA is crucial. Hence, a non-invasive imaging biomarker to detect CA with high specificity is desired. Herein, we evaluated brain 2-deoxy-2-[18F]fluoro-D-glucose (18F-FDG) PET in detecting CA based on cerebellar uptake using receiver operating characteristic (ROC) analysis and five-fold cross-validation.

METHODS

This study was based on STARD 2015 guidelines: thirty patients with anti-GAD65-associated neurological disorders, 11 of whom with CA were studied. Five test sets were created after patients were randomly sorted and divided into 5 equal folds. Each iteration included 24 patients for ROC analysis and 6 patients reserved for testing. The Z scores of left cerebellum, vermis, right cerebellum, and the average of the three regions were used in ROC analysis to determine areas with significant area under the curve (AUC). The cut-off values with high specificity were determined among the 24 patients in each iteration and tested against the reserved 6 patients.

RESULTS

Left cerebellum and average of the three regions showed significant AUC above 0.5 in all iterations with left cerebellum being the highest AUC in 4 iterations. Testing the cut-off values of the left cerebellum against the reserved 6 patients in each iteration showed 100% specificity with sensitivities ranging from 0 to 75%.

CONCLUSIONS

Cerebellar 18F-FDG PET uptake can differentiate CA phenotypes from patients with SPS with high specificity.

Rare presentation of anti-GAD-65 antibody-positive autoimmune encephalitis and simultaneous onset of type 1 diabetes mellitus in a paediatric patient

A 16-year-old female patient presented with subacute onset of headaches, changes in acute mental status, expressive aphasia and auditory hallucinations. New oedema and enhancement of the temporal lobe were seen on brain MRI, with correlating subclinical seizures seen on electroencephalogram. Simultaneously, our patient was diagnosed with new-onset type 1 diabetes mellitus, with positive anti-glutamic acid decarboxylase (anti-GAD-65) antibodies in the serum. Cerebrospinal fluid studies remained negative, including anti-GAD-65 antibodies. Clinical remission was achieved with corticosteroids and intravenous immunoglobulins.

Immune-mediated Cerebellar Ataxias: Practical Guidelines and Therapeutic Challenges

Immune-mediated cerebellar ataxias (IMCAs), a clinical entity reported for the first time in the 1980s, include gluten ataxia (GA), paraneoplastic cerebellar degenerations (PCDs), antiglutamate decarboxylase 65 (GAD) antibody-associated cerebellar ataxia, post-infectious cerebellitis, and opsoclonus myoclonus syndrome (OMS). These IMCAs share common features with regard to therapeutic approaches. When certain factors trigger immune processes, elimination of the antigen( s) becomes a priority: e.g., gluten-free diet in GA and surgical excision of the primary tumor in PCDs. Furthermore, various immunotherapeutic modalities (e.g., steroids, immunoglobulins, plasmapheresis, immunosuppressants, rituximab) should be considered alone or in combination to prevent the progression of the IMCAs. There is no evidence of significant differences in terms of response and prognosis among the various types of immunotherapies. Treatment introduced at an early stage, when CAs or cerebellar atrophy is mild, is associated with better prognosis. Preservation of the "cerebellar reserve" is necessary for the improvement of CAs and resilience of the cerebellar networks. In this regard, we emphasize the therapeutic principle of "Time is Cerebellum" in IMCAs.

The role of the laboratory in the expanding field of neuroimmunology: Autoantibodies to neural targets

Accelerated identification of autoantibodies associated with previously idiopathic neurological disease has provided insights into disease mechanisms, enhanced understanding of neurological function, and opportunities for improved therapeutic interventions. The role of the laboratory in the expanding field of neuroimmunology is critical as specific autoantibody identification provides guidance to clinicians in diagnosis, prognosis, tumor search strategies, and therapeutic interventions. The number of specific autoantibodies identified continues to increase and newer testing strategies increase efficiencies in the laboratory and availability to clinicians. The need for broadly targeted efficient testing is underscored by the variability in clinical presentation and tumor associations attributable to a specific autoantibody, and conversely the various autoantibody specificities that can be the cause of a given clinical presentation. While many of the antineural antibodies were first recognized in the setting of neoplastic disease, idiopathic autoimmune neurological disease in the absence of underlying tumor is increasingly recognized. Appropriation of therapeutic modalities used to treat autoimmune disease to treat these autoantibody mediated neurological diseases has improved patient outcomes. Interaction between clinicians and laboratorians is critical to our understanding of these diseases and optimization of the clinical benefits of our increasing knowledge in neuroimmunology.

Antiglutamic acid decarboxylase 65 (GAD65) antibody-associated epilepsy

Glutamic acid decarboxylase (GAD) antibody-associated encephalitis causes both acute seizures and chronic epilepsy with predominantly temporal lobe onset. This condition is challenging in diagnosis and management, and the incidence of GAD antibody (Ab)-related epilepsy could be much higher than commonly believed. Imaging and CSF evidence of inflammation along with typical clinical presentations, such as adult onset temporal lobe epilepsy (TLE) with unexplained etiology, should prompt testing for the diagnostic antibodies. High serum GAD Ab titer (≥2000U/mL or ≥20nmol/L) and evidence of intrathecal anti-GAD Ab synthesis support the diagnosis. Unlike other immune-mediated epilepsies, antiglutamic acid decarboxylase 65 (GAD65) antibody-mediated epilepsy is often poorly responsive to antiepileptic drugs (AEDs) and only moderately responsive to immune therapy with steroids, intravenous immunoglobulin (IVIG), or plasma exchange (PLEX). Long-term treatment with more aggressive immunosuppressants such as rituximab (RTX) and/or cyclophosphamide is often necessary and may be more effective than current immunosuppressive approaches. The aim of this review is to review the physiology, pathology, clinical presentation, related ancillary tests, and management of GAD Ab-associated autoimmune epilepsy by searching the keywords and to promote the recognition and the initiation of proper therapy for this condition.

Neurologic disorders associated with anti-glutamic acid decarboxylase antibodies: A comparison of anti-GAD antibody titers and time-dependent changes between neurologic disease and type I diabetes mellitus

To determine clinical features of neurologic disorders associated with anti-glutamic acid decarboxylase antibodies (anti-GAD-Ab), we examined titers and time-dependent changes of anti-GAD-Ab. Six patients, stiff person syndrome (2), cerebellar ataxia (1), limbic encephalitis (1), epilepsy (1), brainstem encephalitis (1), were compared with 87 type I diabetes mellitus (T1DM) patients without neurologic disorders. Anti-GAD-Ab titers and index were higher in neurologic disorders than in T1DM, suggesting intrathecal antibody synthesis. Anti-GAD-Ab titers in T1DM decreased over time, whereas they remained high in neurologic disorders. Immunotherapy improved neurological disorders and anti-GAD-Ab titers and index provide clinically meaningful information about their diagnostic accuracy.

Adenocarcinoma of Lung Presenting as Lambert-Eaton Myasthenic Syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is a paraneoplastic neuromuscular junction disorder. LEMS presents with muscular weakness and fatigability, mainly involving the proximal lower limbs. There are 2 types of LEMS depending on the etiology: paraneoplastic and idiopathic. The paraneoplastic form, which constitutes more than a half of the cases, is mostly associated with intrathoracic neoplasms. Most cases are seen in patients with small cell lung cancer; other subtypes of lung cancer are extremely rare. In this article, we report a case of LEMS as a rare association with adenocarcinoma of the lung.

Cerebellar disease associated with anti-glutamic acid decarboxylase antibodies: review

Several neurological syndromes have been recognized associated to GAD antibodies. Among those disorders, cerebellar ataxia (CA) is one of the most common, along with stiff-person syndrome. Patients with GAD associated CA present with a progressive pancerebellar syndrome, with a subacute or chronic evolution, along with other neurological manifestations such as stiffness, oculomotor dysfunction, epilepsy, and cognitive dysfunction. These symptoms may be preceded by the so-called "brainstem attacks", where manifestations consistent with transient dysfunction of the brainstem may be observed. These patients frequently have extra-neurologic autoimmune manifestations such as diabetes mellitus type 1, polyendocrine autoimmune syndrome, pernicious anemia, vitiligo, etc. A proportion of patients may present with an underlying neoplasia, but the course is less aggressive than in those patients with classical paraneoplastic CA with onconeural antibodies. The diagnosis is based on the present of high serum and CSF titers of GAD antibodies, with intrathecal production of such antibodies. Treatment is aimed to decrease the immunological response with intravenous immunoglobulin, steroids, rituximab and oral immunosuppressive drugs. A subacute presentation and rapid initiation of immunotherapy seem to be the predictors of a favorable clinical response.

Low-Titre GAD Antibody-Associated Late-Onset Cerebellar Ataxia with a Significant Clinical Response to Intravenous Immunoglobulin Treatment

Antiglutamic acid decarboxylase antibody-associated cerebellar ataxia (GAD-Abs CA) is a rare, but increasingly detected, autoimmune neurological disorder characterized by the clinical presence of a cerebellar syndrome concomitant with positive GAD-Abs levels in serum and cerebrospinal fluid (CSF). It represents 3% of all immune-mediated sporadic CAs. Low-titre GAD-Abs CA is an even rarer subtype of GAD-Abs CA. We report on a 68-year-old woman with a 3-year history of progressive gait ataxia. In addition to the modified Rankin Scale (mRS), we used two other objective scales to evaluate CA severity, i.e. the International Cooperative Ataxia Rating Scale (ICARS) and the Scale for Assessment and Rating of Ataxia (SARA). Series of CT and MRI showed atrophy of the cerebellum. Except for the glycated haemoglobin (HbA_1c) levels, all other routine laboratory examinations were within normal limits. Autoimmune laboratory examinations showed positive (25.8 U/mL) serum GAD-Abs levels. The GAD antibody index was <1.0. The CSF analysis showed no oligoclonal immunoglobulin bands. Intravenous immunoglobulin (IVIg) therapy was started and significant improvement was observed. The diagnosis of low-titre GAD-Abs CA was established.

Guidelines for treatment of immune-mediated cerebellar ataxias

Immune-mediated cerebellar ataxias include gluten ataxia, paraneoplastic cerebellar degeneration, GAD antibody associated cerebellar ataxia, and Hashimoto’s encephalopathy. Despite the identification of an increasing number of immune-mediated cerebellar ataxias, there is no proposed standardized therapy. We evaluated the efficacies of immunotherapies in reported cases using a common scale of daily activity. The analysis highlighted the importance of removal of autoimmune triggering factors (e.g., gluten or cancer) and the need for immunotherapy evaluation (e.g., corticosteroids, intravenous immunoglobulin, immunosuppressants) and adaptation according to each subtype.

[Clinical characteristics of four patients with temporal lobe epilepsy associated with elevated anti-GAD antibodies]

Anti-glutamic acid decarboxylase (GAD) antibodies are known to be associated with insulin-dependent diabetes mellitus (IDDM), stiff-person syndrome, and other neurological symptoms including temporal lobe epilepsy (TLE), known as autoimmune epilepsy. We treated four patients with TLE who had elevated titers of serum anti-GAD antibody (anti-GAD-Ab), higher than 100 U/ml. Three of the four patients started to have epileptic seizures in their 5th or 6th decade. Characteristic symptoms suggesting encephalitis or encephalopathy were absent at onset of these symptoms, which led to delayed diagnosis. All four patients developed two or three of cerebellar ataxia, neuropsychological impairment, and IDDM, by several years or decades after onset of TLE, even after seizure freedom in two patients. These abnormalities were indicators for suspecting the involvement of anti-GAD-Ab in the pathogenesis. Anti-GAD-Ab levels in the cerebrospinal fluid (CSF) were measured, which detected elevated CSF/serum anti-GAD-Ab ratio (≥ 1.0), suggesting intrathecal anti-GAD-Ab synthesis, in three of the four patients. The TLE symptoms were somewhat prolonged, but three of the four patients eventually achieved seizure freedom after immunotherapies with combinations of two or three anti-epileptic drugs. Serum anti-GAD Ab is recommended to be measured in patients with middle-aged onset TLE. Moreover, immune-modulating therapies including steroid pulse and intravenous immunoglobulin therapies could have ameliorated neurological complications, even in the chronic phase.

Ataxia

Ataxia is a disorder of balance and coordination resulted from dysfunctions involving cerebellum and its afferent and efferent connections. While a variety of disorders can cause secondary ataxias, the list of genetic causes of ataxias is growing longer. Genetic abnormalities may involve mitochondrial dysfunction, oxidative stress, abnormal mechanisms of DNA repair, possible protein misfolding, and abnormalities in cytoskeletal proteins. Few ataxias are fully treatable while hope for efficacious gene therapy and pharmacotherapy is emerging. A discussion of the ataxias is presented here with brief mention of acquired ataxias, and a greater focus on inherited ataxias.

Limbic encephalitis with antibodies to glutamic acid decarboxylase presenting with brainstem symptoms

Limbic encephalitis (LE) is a neurological syndrome that may present in association with cancer, infection, or as an isolate clinical condition often accompanying autoimmune disorders. LE associated with glutamic acid decarboxylase antibodies (anti-GAD) is rare in children. Here, we characterized the clinical and laboratory features of a patient presenting with brainstem involvement with non-paraneoplastic LE associated with anti-GAD antibodies. In our patient, after plasma exchange, we determined a dramatic improvement of the neurological deficits.

No Overlap among Serum GAD65, NMDAR and AQP4 Antibodies in Patients with Neuromyelitis Optica Spectrum Disorders

OBJECTIVE

To evaluate whether serum glutamic acid decarboxylase (GAD), N-methyl-D-aspartate-receptor (NMDAR), and aquaporin-4 (AQP4) autoantibodies coexist in patients with neuromyelitis optica (NMO)/NMO spectrum disorders (NMOSD).

METHODS

Serum samples were collected from 98 patients with NMO/NMOSD. Serum GAD65, NMDAR and AQP4 antibodies were measured using a cell-based assay.

RESULTS

A total of 63 patients (64.3%) had myelitis and optic neuritis and satisfied the revised diagnostic criteria for NMO. Longitudinally extensive transverse myelitis was seen on spinal cord magnetic resonance imaging, showing continuous T2-weighted signal abnormalities in at least three vertebral segments in 26 patients (26.5%); 5 patients (5.1%) had recurrent optic neuritis, and 4 patients (4.1%) had brain syndromes with optic neuritis and myelitis. None of the 98 patients had diabetes, stiff-man syndrome, or epilepsy. All 98 patients tested positive for AQP4 antibody. No patients tested positive for GAD65 and NMDAR antibodies.

CONCLUSIONS

In the present study, we found no simultaneous presence of serum GAD65, NMDAR and AQP4 antibodies in patients with NMO/NMOSD.

Cerebellar ataxia and glutamic acid decarboxylase antibodies: immunologic profile and long-term effect of immunotherapy

IMPORTANCE

Current clinical and immunologic knowledge on cerebellar ataxia (CA) with glutamic acid decarboxylase 65 antibodies (GAD65-Abs) is based on case reports and small series with short-term follow-up data.

OBJECTIVE

To report the symptoms, additional antibodies, prognostic factors, and long-term outcomes in a cohort of patients with CA and GAD65-Abs.

DESIGN, SETTING, AND PARTICIPANTS

Retrospective cohort study and laboratory investigations at a center for autoimmune neurologic disorders among 34 patients with CA and GAD65-Abs, including 25 with long-term follow-up data (median, 5.4 years; interquartile range, 3.1-10.3 years).

MAIN OUTCOMES AND MEASURES

Analysis of clinicoimmunologic features and predictors of response to immunotherapy. Immunochemistry on rat brain, cultured neurons, and human embryonic kidney cells expressing GAD65, GAD67, α1-subunit of the glycine receptor, and a repertoire of known cell surface autoantigens were used to identify additional antibodies. Twenty-eight patients with stiff person syndrome and GAD65-Abs served as controls.

RESULTS

The median age of patients was 58 years (range, 33-80 years); 28 of 34 patients (82%) were women. Nine patients (26%) reported episodes of brainstem and cerebellar dysfunction or persistent vertigo several months before developing CA. The clinical presentation was subacute during a period of weeks in 13 patients (38%). Nine patients (26%) had coexisting stiff person syndrome symptoms. Systemic organ-specific autoimmunities (type 1 diabetes mellitus and others) were present in 29 patients (85%). Twenty of 25 patients with long-term follow-up data received immunotherapy (intravenous immunoglobulin in 10 and corticosteroids and intravenous immunoglobulin or other immunosuppressors in 10), and 7 of them (35%) improved. Predictors of clinical response included subacute onset of CA (odds ratio [OR], 0.50; 95% CI, 0.25-0.99; P = .047) and prompt immunotherapy (OR, 0.98; 95% CI, 0.96-0.99; P = .01). Similar frequencies of serum GAD67-Abs were found in patients with CA (24 of 34 patients [71%]) and in patients with stiff person syndrome (20 of 28 patients [71%]). However, GAD67-Abs were found in all of the cerebrospinal fluid samples examined (22 samples from patients with CA and 17 samples from patients with stiff person syndrome). Glycine receptor antibodies but not other cell surface antibodies were identified in 4 patients with CA. The presence of glycine receptor antibodies did not correlate with any specific clinical feature.

CONCLUSIONS AND RELEVANCE

In patients with CA and GAD65-Abs, subacute onset of symptoms and prompt immunotherapy are associated with good outcome. Persistent vertigo or brainstem and cerebellar episodes can herald CA and should lead to GAD65-Ab testing, particularly in patients with systemic organ-specific autoimmunities.

Monoclonal antibodies to 65kDa glutamate decarboxylase induce epitope specific effects on motor and cognitive functions in rats

Background

Stiff Person Syndrome (SPS) is a rare autoimmune movement disorder characterized by the presence of autoantibodies specific to the smaller isoform of glutamate decarboxylase (GAD65). A pathological role of these antibodies has been suggested by their capacity to inhibit GAD65 enzyme activity and by the observation that rats receiving cerebellar injections of GAD65Ab showed cerebellar motor hyperexcitability. To assess the effect of epitope-specific GAD65Ab on cognitive and motor functions, we conducted behavioral experiments in rats that received cerebellar injections with two distinct monoclonal GAD65Ab (b96.11 and b78).

Methods

Rats received three injections of GAD65Ab b96.11 (5 or 7 μg), GAD65Ab b78 (5 or 7 μg), or saline at the level of three cerebellar nuclei. Animals were submitted to neurological evaluation and Morris Water Maze (MWM) test. Cellular internalization of GAD65Ab was analyzed by Flow Cytometry, Fluorescence and Bright Field microscopy.

Results

Monoclonal GAD65Ab induced dose-dependent and epitope-specific effects on motor and cognitive functions. Injections of the higher dose altered motor and spatial procedural behaviors, while the lower dose induced only modest cerebellar motor symptoms and did not affect MWM performances. While b96.11 provoked immediate severe effects, which rapidly decreased, b78 induced moderate but prolonged effects. Both GAD65Ab were taken up by live cells in a dose-dependent manner.

Conclusions

Our findings support the hypothesis that epitope-specific GAD65Ab induce cerebellar dysfunction impairing motor and procedural abilities. This is the first demonstration of a critical role of cerebellar nuclei GAD65 enzyme in procedural spatial functions.

Neurological disorders associated with glutamic acid decarboxylase antibodies: a Brazilian series

Neurological disorders associated with glutamic acid decarboxylase (GAD) antibodies are rare pleomorphic diseases of uncertain cause, of which stiff-person syndrome (SPS) is the best-known. Here, we described nine consecutive cases of neurological disorders associated with anti-GAD, including nine patients with SPS and three cases with cerebellar ataxia. Additionally, four had hypothyroidism, three epilepsy, two diabetes mellitus and two axial myoclonus.

Autoimmune stiff person syndrome and related myelopathies: understanding of electrophysiological and immunological processes

Stiff person syndrome (SPS) is a disabling autoimmune central nervous system disorder characterized by progressive muscle rigidity and gait impairment with superimposed painful spasms that involve axial and limb musculature, triggered by heightened sensitivity to external stimuli. Impaired synaptic GABAergic inhibition resulting from intrathecal B-cell-mediated clonal synthesis of autoantibodies against various presynaptic and synaptic proteins in the inhibitory neurons of the brain and spinal cord is believed to be an underlying pathogenic mechanism. SPS is most often idiopathic, but it can occur as a paraneoplastic condition. Despite evidence that anti-GAD and related autoantibodies impair GABA synthesis, the exact pathogenic mechanism of SPS is not fully elucidated. The strong association with several MHC-II alleles and improvement of symptoms with immune-modulating therapies support an autoimmune etiology of SPS. In this review, we discuss the clinical spectrum, neurophysiological mechanisms, and therapeutic options, including a rationale for agents that modulate B-cell function in SPS.

Stiff person syndrome: advances in pathogenesis and therapeutic interventions

Stiff person syndrome (SPS) varies from mild to severe, but if untreated it can be progressive and disabling. Although progress has been made in understanding and treating SPS, the disease remains underdiagnosed, delaying treatment. Antibodies against glutamic acid decarboxylase provide an excellent diagnostic marker, but their role in disease pathogenesis is uncertain. Research focused on identifying new autoantigens has provided evidence that gamma-aminobutyric acid (GABA)(A) receptor-associated protein (GABARAP), a 14-kD protein localized at the postsynaptic regions of GABAergic synapses, is an antigenic target. Circulating anti-GABARAP antibodies that inhibit GABA(A) receptor expression on GABAergic neurons have been found in up to 65% of SPS patients. The impairment of GABAergic pathways and reduction of brain GABA results in clinical manifestations of stiffness, spasms, and phobias. Increased awareness of SPS among practicing physicians is necessary to recognize the disease early and prevent permanent disability. Most patients with SPS respond to GABA-enhancing drugs, but the high doses required cause unacceptable adverse effects. The disease clearly responds to intravenous immunoglobulin, but repeated infusions are needed to maintain response. New immunomodulating agents are being explored to treat difficult cases and to induce long-lasting remissions.

Anti-glutamic Acid decarboxylase antibody-associated ataxia as an extrahepatic autoimmune manifestation of hepatitis C infection: a case report

Extrahepatic immunological manifestations of hepatitis C virus (HCV) are well described. In addition, antiglutamic acid decarboxylase (GAD) antibody-associated cerebellar ataxia is well-established entity. However, there have been no reports in the literature of anti-GAD antibody-associated ataxia as an extrahepatic manifestation of HCV infection. We report the case of a young woman with chronic hepatitis C virus and multiple extrahepatic autoimmune diseases including Sjögren syndrome and pernicious anemia who presented with subacute midline cerebellar syndrome and was found to have positive antiglutamic acid decarboxylase (GAD) antibody in the serum and cerebrospinal fluid. An extensive diagnostic workup to rule out neoplastic growths was negative, suggesting the diagnosis of nonparaneoplastic antiglutamic acid decarboxylase antibody-associated cerebellar ataxia as an additional extrahepatic manifestation of hepatitis C virus infection. The patient failed to respond to high-dose steroids and intravenous immunoglobulin. Treatment with the monoclonal antibody rituximab stabilized the disease. We postulate that anti-GAD associated ataxia could be an extrahepatic manifestation of HCV infection.

Clinical presentation of immune-mediated cerebellar ataxia

INTRODUCTION

Accumulation of recent clinical evidence indicates that the immune system plays an important role in some central nervous system diseases usually regarded as degenerative. The most striking example is paraneoplastic cerebellar ataxia (PCA), which is characterized by autoimmune cross-reaction between tumoral and nervous system antigens.

STATE OF THE ART

In the past 20 years, several antibodies directed against neuronal and tumoral antigens have been described in association with PCA, leading to the description of different subtypes of PCA based on the associated antibodies, the clinical course and the type of tumor. In some subtypes, cerebellar ataxia occurs in isolation, whereas in others, cerebellar ataxia is a syndrome that occurs in conjunction with extensive nervous system disease. Circulating antibodies have also been described in patients with non-paraneoplastic cerebellar ataxia (N-PCA), suggesting that the immune system may be involved in certain cases of sporadic cerebellar ataxia.

PERSPECTIVE

Immune-mediated cerebellar ataxia does not seem to be limited to paraneoplastic neurological syndromes. Further studies are however necessary to understand the exact pathophysiology of these disorders and offer effective treatments.

CONCLUSION

In this review, the clinical presentation of the different subtypes of potentially immune-mediated PCA and N-PCA will be described, and the associated tumors will be discussed.

[A case of immune-mediated encephalopathy showing refractory epilepsy and extensive brain MRI lesions associated with anti-glutamic acid decarboxylase antibody]

We reported a patient with immune-mediated encephalopathy showing refractory epilepsy and multiple brain lesions on MRI. The patient had high titers of anti-glutamic acid decarboxylase (GAD) antibody in sera and cerebrospinal fluid (CSF). A 36-year-old previously healthy woman was admitted to our hospital with onset of sudden generalized seizure that then persisted for one month. She had repeated epileptic attacks accompanied with loss of consciousness, and was refractory to valproic acid, zonisamide (200 mg/day) and phenobarbital (200 mg/day). Brain MRI showed multiple hyperintense lesions in predominantly bilateral frontal lobes, parietal lobes, occipital lobes and cingulate cortices. EEG showed epileptic activities (frequent sharp waves) in bilateral frontal regions. After admission, attacks disappeared through the administration of clonazepam (1.5 mg/day), though the patient remained slightly disoriented. As titers of anti-GAD antibody in sera and CSF were extremely high, we implemented plasma exchanges. After treatment, titers of anti-GAD antibody in sera and CSF decreased. The patient completely recovered to an alert state and the abnormal MRI lesions almost disappeared. Since GAD catalyzes production of gamma-aminobutyric acid (GABA), it is proposed that anti-GAD antibodies reduce synthesis of GABA or interferes with exocytosis of GABA in the nervous system. Anti-GAD antibodies are detected in some rare neurological disorders such as stiff-person syndrome. Recently, anti-GAD antibodies have been reported as implicated in cerebellar ataxia, palatal myoclonus, refractory epilepsy and limbic encephalitis. Epilepsy associated with the anti-GAD antibody is mostly pharmacoresistant temporal lobe epilepsy; with brain MRI showing no abnormality or only hippocampal sclerosis. It is very rare that brain MRI shows extensive abnormal lesions except in the hippocampus. This case suggests that anti-GAD antibodies could contribute to unexplained encephalopathy with extensive brain MRI lesions and drug-resistant symptomatic epilepsy.

Clinical significance of glutamic acid decarboxylase antibodies in patients with epilepsy

PURPOSE

Glutamic acid decarboxylase antibodies (GADAs) have been detected in patients with epilepsy, but the clinical determinants of epilepsy associated with GADA have not been defined.

METHODS

We analyzed GADA with a radioimmunoassay in sera of 253 well-characterized patients with epilepsy and 200 control subjects. The positive samples were confirmed by immunohistochemistry and western blotting (WB). Sera were screened for other autoantibodies.

RESULTS

GADA were detected in 15 patients (5.9%) and in three control subjects (1.5%) (p = 0.026). Seven patients (2.8%) had high GADA titers [>or=1,000 relative units (RUs)/ml], six of whom had temporal lobe epilepsy (TLE). All three GADA-positive control subjects had low titers. Two of the five patients with high GADA titers and available cerebrospinal fluid (CSF) samples had intrathecal synthesis (IS) of GADA; one patient had CSF oligoclonal bands. The prevalence of increased levels of GADA tended to be higher in patients with TLE than in patients with extra-TLE [odds ratio (OR) 1.32, 95% confidence interval (CI) 0.39-4.42; p = 0.657]. The patients with high GADA titers had significantly higher number of other autoantibodies compared to the patients with low GADA titers (p = 0.001) and the patients with normal GADA (p < 0.001).

DISCUSSION

High GADA titers were present in a subgroup of patients; close to 90% had TLE. The immunologic profile of these patients suggests that the most probable origin of their epilepsy is autoimmune. A positive IS of GADA may be a marker of an ongoing immune response that could identify those patients in whom a trial with immunosuppressive therapy might be warranted.

Limbic encephalitis associated with anti-GAD antibody and common variable immune deficiency

A variety of autoantibodies have been identified with complex neurological disorders including limbic encephalitis. The underlying trigger for the immune-mediated process and the role of autoantibodies in the pathogenesis of limbic encephalitis remain to be clarified. Here, we report a 16-year-old female who was diagnosed with acute-onset non-neoplastic limbic encephalitis. The initial treatment with pulse doses of i.v. methylprednisolone improved the neurological symptoms. During the next 12 months, progressive decline was reported in her academic functioning and seizure control. Additional diagnostic evaluation revealed no evidence of malignancy or central nervous system infection but circulating anti-GAD antibodies were present in the serum and cerebrospinal fluid. Intravenous gammaglobulin infusion was initiated and continued monthly. Intravenous and oral steroids were added to the intravenous immunoglobulin treatment because of the worsening course and seizures, despite treatment with antiepileptic medications. Screening for quantitative immunoglobulins demonstrated hypogammaglobulinaemia with low immunoglobulin M and G in addition to low immunoglobulin A levels. There was a lack of protective pneumococcal antibody titers before and after immunization. Therefore, common variable immunodeficiency was suspected despite there being no history of recurrent infections. To our knowledge, this is the first report describing a possible link between immune-mediated limbic encephalitis and immune deficiency.

Intravenous immunoglobulin therapy for autoantibody-positive cerebellar ataxia

OBJECTIVE

It has been reported that autoimmune cerebellar ataxias, such as anti-glutamic acid decarboxylase (GAD)-antibody-positive cerebellar ataxia and gluten ataxia, are treatable. Here, we examined the therapeutic efficacy of intravenous immunoglobulin (IVIg) on autoantibody-positive cerebellar ataxia.

PATIENTS AND METHODS

IVIg therapy was administered in seven autoantibody-positive cerebellar ataxia patients. Therapeutic efficacy was examined in terms of its effects on clinical symptoms and changes in brain perfusion using single photon emission computed tomography (SPECT).

RESULTS

Treatment was effective in four cerebellar cortical atrophy patients (two anti-GAD antibody-positive and two anti-gliadin antibody-positive) and in one anti-thyroid antibody-positive spinocerebellar ataxia type 3 (SCA3) patient, but not in two multiple system atrophy (MSA) patients. All four IVIg effective patients who underwent SPECT showed apparent increases in cerebellar perfusion.

CONCLUSION

If cerebellar ataxia with an autoimmune mechanism is suspected and radiological findings do not reveal MSA, it is worth considering immunotherapy including IVIg.

Advances in the pathogenesis and treatment of patients with stiff person syndrome

Advances in the clinical diagnosis, prognosis, pathogenesis, and therapies for stiff person syndrome (SPS), based on observations in more than 50 consecutive patients, are presented. The syndrome varies from mild to severe, but if untreated it can be progressive and disabling. SPS remains a largely underdiagnosed condition. Anti-glutamic acid decarboxylase (GAD) antibodies provide an excellent diagnostic marker, but their role in disease pathogenesis is uncertain. Research focused on identifying new autoantigens has provided evidence that gamma-aminobutyric acid (GABA)(A) receptor-associated protein (GABARAP), a 14-kD protein localized at the postsynaptic regions of GABAergic synapses, is a new antigenic target. In up to 65% of SPS patients, there are circulating anti-GABARAP antibodies that inhibit the GABA(A) receptor expression on GABAergic neurons. This review examines the diagnostic criteria for SPS, SPS variants, common errors in diagnosis, and a step-by-step therapeutic approach, including new advances in therapy.

Ocular motor syndromes of the brainstem and cerebellum

PURPOSE OF REVIEW

The brainstem and cerebellum contain many neuronal types that play a critical role in eye movement control. In a physiological approach, understanding how these neuronal assemblies cooperate provides strong insight into general brain functions. Furthermore, eye movements provide an interesting model for understanding neural mechanisms of sensorimotor learning, and a knowledge of the mechanisms underlying oculomotor plasticity is essential for correctly diagnosing and effectively managing patients. Finally, knowledge of the ocular motor syndromes frequently helps localize the pathological abnormality.

RECENT FINDINGS

We review the recently published works dealing with the physiological organization and pathology of slow and rapid eye movements at a brainstem and cerebellar level.

SUMMARY

The main recent findings of great interest for clinical practice or research concern the physiopathology of head shaking nystagmus, downbeat nystagmus and oculopalatal tremor; the neural substrates of three-dimensional control of eye movements and of optokinetic nystagmus; the understanding of saccade generation and of its consequences on physiological and pathological eye oscillations; and, finally, the physiological basis of saccadic adaptation.