Autoantibodies to glutamic acid decarboxylase in palatal myoclonus and epilepsy

Seizure semiology and predictors of outcomes in Chinese patients with glutamic acid decarboxylase antibody-associated neurological syndrome

BACKGROUND

In the current study, seizure semiology and potential predictive factors of seizure outcomes in glutamic acid decarboxylase antibody (GAD Ab)-associated neurological syndrome were investigated.

METHODS

In this study, 32 Chinese patients with GAD Ab-associated neurological syndrome who presented with seizures at Peking Union Medical College Hospital from January 2017 to October 2022 were reviewed; 30 had a follow-up duration of more than 1 year.

RESULTS

Among the 32 patients, 10 presented with epilepsy alone. Concomitant neurological syndromes were observed in 22 patients, including limbic encephalitis (n = 20), stiff-person syndrome (SPS, n = 1), and cerebellar ataxia (n = 1). Bilateral tonic-clonic seizures were observed in 21 patients (65.6%). Focal seizures occurred in 27 patients (84.4%); 17 had focal motor seizures and 18 focal non-motor seizures. Among 30 patients with long-term follow-up, 11 (36.7%) were seizure-free. Acute/subacute onset (p = 0.049) and comorbidity of limbic encephalitis with epilepsy (p = 0.023) led to better seizure outcomes. Patients with persistent epilepsy were more likely to have focal seizure (p = 0.003) and higher frequency of seizure (p = 0.001). Furthermore, these patients tended to have longer intervals from onset to immunomodulatory treatments. Early immunotherapy (within 6 months from onset) was administered in 81.8% of seizure-free patients but only in 42.1% of patients with persistent seizures. However, steroid and immunosuppressant duration did not differ in the two groups. Repeated serum GAD Ab tests during the follow-up showed no association with seizure outcomes.

CONCLUSIONS

The seizure manifestations are diverse and variable. Approximately one third of patients achieved seizure remission during long-term follow-up. The type and frequency of seizures may influence the seizure outcomes. Early immunotherapy, especially within 6 months, may lead to better seizure outcomes.

Glutamic acid decarboxylase 65-positive autoimmune encephalitis presenting with gelastic seizure, responsive to steroid: A case report

BACKGROUND

Anti-glutamic acid decarboxylase (GAD) antibody is known to cause several autoimmune-related situations. The most known relationship is that it may cause type I diabetes. In addition, it was also reported to result in several neurologic syndromes including stiff person syndrome, cerebellar ataxia, and autoimmune encephalitis. Decades ago, isolated epilepsy associated with anti-GAD antibody was first reported. Recently, the association between temporal lobe epilepsy and anti-GAD antibody has been discussed. Currently, with improvements in examination technique, many more autoimmune-related disorders can be diagnosed and treated easier than in the past.

CASE SUMMARY

A 44-year-old female Asian with a history of end-stage renal disease (without diabetes mellitus) under hemodialysis presented with diffuse abdominal pain. The initial diagnosis was peritonitis complicated with sepsis and paralytic ileus. Her peritonitis was treated and she recovered well, but seizure attack was noticed during hospitalization. The clinical impression was gelastic seizure with the presentation of frequent smiling, head turned to the right side, and eyes staring without focus; the duration was about 5–10 s. Temporal lobe epilepsy was recorded through electroencephalogram, and she was later diagnosed with anti-GAD65 antibody positive autoimmune encephalitis. Her seizure was treated initially with several anticonvulsants but with poor response. However, she showed excellent response to intravenous methylprednisolone pulse therapy. Her consciousness returned to normal, and no more seizures were recorded after 5 d of intravenous methylprednisolone treatment.

CONCLUSION

In any case presenting with new-onset epilepsy, in addition to performing routine brain imaging to exclude structural lesion and cerebrospinal fluid studies to exclude common etiologies of infection and inflammation, checking the autoimmune profile has to be considered. In the practice of modern medicine, autoimmune-related disorders are relatively treatable and should not be missed.

Serum glutamate decarboxylase antibodies and neurological disorders: when to suspect their association?

OBJECTIVES

To explore different neurological manifestations with suspicion of being associated to serum glutamate decarboxylase antibodies (GAD-Abs) in order to better characterize anti-GAD neurological syndromes.

METHODS

Observational retrospective study including all patients for whom GAD65-Abs titers in serum were requested by the Neurology Department at La Paz University Hospital between 2015 and 2019. GAD-Abs were measured by ELISA. Demographic data, neurological symptoms, comorbidity with diabetes mellitus (DM) or with another autoimmune disease, and GAD-Abs titers were studied. Stiff-person syndrome, ataxia, encephalitis, and epilepsy were considered typical anti-GAD neurological syndromes and were compared to other atypical manifestations.

RESULTS

A total of 173 patients (51.7% men, mean age 51.62) were included. A progressive increase in requests of serum GAD-Abs has occurred over the last 5 years, especially in patients with atypical neurological manifestations. GAD-Abs were found in the serum of 22 patients (12.7%); of those, 15 (68.18%) suffered a typical anti-GAD syndrome. Presence of DM or another organ-specific autoimmune disease was predictive of GAD-AB seropositivity (p < 0.001). 6.6% of requested patients with an atypical syndrome had GAD-Abs, but serum levels were significantly lower than those found in patients with a typical syndrome (706.67 vs 1430.23 UI/mL; Mann-Whitney U, p = 0.034), and were finally diagnosed with another neurological disease.

CONCLUSION

Serum GAD-Abs were infrequently found in patients with clinical phenotypes other than those classically described as anti-GAD disorders, and with very low titers. In typical anti-GAD syndromes, there is a high comorbidity with DM and with other autoimmune diseases, and high serum GAD-Abs levels are usually present.

Neurological Syndromes Associated with Anti-GAD Antibodies

Glutamic acid decarboxylase (GAD) is an intracellular enzyme whose physiologic function is the decarboxylation of glutamate to gamma-aminobutyric acid (GABA), the main inhibitory neurotransmitter within the central nervous system. GAD antibodies (Ab) have been associated with multiple neurological syndromes, including stiff-person syndrome, cerebellar ataxia, and limbic encephalitis, which are all considered to result from reduced GABAergic transmission. The pathogenic role of GAD Ab is still debated, and some evidence suggests that GAD autoimmunity might primarily be cell-mediated. Diagnosis relies on the detection of high titers of GAD Ab in serum and/or in the detection of GAD Ab in the cerebrospinal fluid. Due to the relative rarity of these syndromes, treatment schemes and predictors of response are poorly defined, highlighting the unmet need for multicentric prospective trials in this population. Here, we reviewed the main clinical characteristics of neurological syndromes associated with GAD Ab, focusing on pathophysiologic mechanisms.

Quantitative clinical and autoimmune assessments in stiff person syndrome: evidence for a progressive disorder

BACKGROUND

Stiff Person Syndrome (SPS) is an under-diagnosed disorder that affects mobility and the quality of life of affected patients. The aim of the study is to describe the natural history of SPS, the extent of accumulated disability and the associated clinical and immunological features in patients followed for up to 8 years in a single center.

METHODS

Our collective cohort included 57 SPS patients. Additionally, 32 of these patients were examined every 6 months for a two-year period in a longitudinal study protocol, to assess disease progression using quantitative measures of stiffness and heightened sensitivity.

RESULTS

The most frequent initial symptom was leg stiffness, followed by paraspinal muscle rigidity and painful spasms in 95% of the patients. Although none of the patients required assistance for ambulation during the first 2 years of disease onset, 46 patients (80%) lost the ability to walk independently during our follow-up, despite symptomatic medications. In the longitudinal cohort, the number of stiff areas increased (p < 0.0001), consistent with worsening functional status and quality of life. High-titer anti-GAD antibodies were present in serum and CSF with elevated intrathecal GAD-specific IgG synthesis, but they did not correlate with clinical severity or progression.

CONCLUSIONS

This large study on SPS patients, combining an eight-year follow-up at a single center by the same leading neurologist and his team, is the first to provide longitudinal data in a large patient subgroup using objective clinical measures. One of the main findings is that SPS is a progressive disease leading to physical disability over time.

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.

Innate and adaptive immunity in human epilepsies

Inflammatory mechanisms have been increasingly implicated in the origin of seizures and epilepsy. These mechanisms are involved in the genesis of encephalitides in which seizures are a common complaint. Experimental and clinical evidence suggests different inflammatory responses in the brains of patients with epilepsy depending on the etiology. In general, activation of both innate and adaptive immunity plays a role in refractory forms of epilepsy. Epilepsies in which seizures develop after infiltration of cells of the adaptive immune system in the central nervous system (CNS) include a broad range of epileptic disorders with different (known or unknown) etiologies. Infiltration of lymphocytes is observed in autoimmune epilepsies, especially the classical paraneoplastic encephalitides with antibodies against intracellular tumor antigens. The presence of lymphocytes in the CNS also has been found in focal cerebral dysplasia type 2 and in cortical tubers. Various autoantibodies have been shown to be associated with temporal lobe epilepsy (TLE) and hippocampal sclerosis of unknown etiology, which may be due to the presence of viral DNA. During the last decade, an increasing number of antineuronal autoantibodies directed against membranous epitopes have been discovered and are associated with various neurologic syndromes, including limbic encephalitis. A major challenge in epilepsy is to define biomarkers, which would allow the recognition of patient populations who might benefit from immune-modulatory therapies. Some peripheral inflammatory markers appear to be differentially expressed in patients with medically controlled and medically refractory and, as such, could be used for diagnostic, prognostic, or therapeutic purposes. Establishing an autoimmune basis in patients with drug-resistant epilepsy allows for efficacious and targeted immunotherapy. Although current immunotherapies can give great benefit to the correctly identified patient, there are limitations to their efficacy and they may have considerable side effects. Thus the identification of new immunomodulatory compounds remains of utmost importance.

[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.

GABA-A receptor impairment in cerebellar ataxia with anti-glutamic acid decarboxylase antibodies

Antibodies against glutamic acid decarboxylase (GAD-Abs) are associated with cerebellar ataxia, which is refractory to treatment with GABAergic drugs. To investigate the GABAergic neuronal system in vivo, we performed a combined positron emission tomography (PET) study with [(11)C]-flumazenil and [(18)F]-fluorodeoxyglucose (FDG) in three patients with cerebellar ataxia with GAD-Abs. The GABA-A receptor function was investigated using flumazenil, which is a selective GABA-A receptor ligand, while FDG-PET using a three-dimensional stereotactic surface projection analysis was performed to estimate the metabolic rates of glucose (MRGlc) in the patients. GABAergic drugs showed no efficacy for the cerebellar ataxia in all three patients, and all three displayed a significant decrease in flumazenil binding in the cerebellum. No MRGlc decrease in the cerebellum was found in the two patients who presented with amelioration of cerebellar ataxia following intravenous immunoglobulin (IVIG) therapy, whereas a significant MRGlc decrease in the cerebellar hemisphere was observed in another patient who showed severe cerebellar atrophy on magnetic resonance images and no response to the IVIG therapy. The decreased flumazenil binding in the present patients indicated cerebellar GABA-A receptor impairment, which may be due to either neuronal cell loss, as demonstrated by the decreased MRGlc, or a dysfunction in GABAergic neuronal inhibition. Although GAD-Abs have been postulated to prevent the synthesis of GABA, resulting in decreased GABAergic transmission, the GABA-A receptor impairment may play another pathogenic role in cerebellar ataxia associated with GAD-Abs resulting in a condition refractory to GABAergic drug therapy.

Peripheral neuropathy associated with antiglutamic acid decarboxylase antibodies

Autoantibodies to glutamic acid decarboxylase are found in some rare neurological diseases. However, acute peripheral neuropathy associated with antiglutamic acid decarboxylase autoimmunity has not been reported previously. Here we report a case of a patient who presented with acute cranial and peripheral neuropathy in association with the presence of serum antiglutamic acid decarboxylase antibodies. A 13-year-old boy was admitted to our pediatric neurology clinic with diplopia due to sixth cranial nerve palsy and ascending motor weakness in all extremities. The nerve conduction studies showed bilateral motor and sensory demyelinating neuropathy. Full recovery was achieved following intravenous immunoglobulin treatment. Glutamic acid decarboxylase autoimmunity-associated neurological diseases spectrum may also include acute demyelinating peripheral neuropathy.

[A case of progressive ataxia and palatal tremor (PAPT) with ear clicks]

A 71-year-old man noted clicking sounds in the ear. At the age of 75, he developed progressive unsteadiness of gait and became unable to walk without assistance at the age of 76. There was no family history of neurologic illness. Neurological examination revealed truncal ataxia and 1-2 Hz rhythmic palatal tremor, which persisted during sleep. Consistently, brain magnetic resonance imaging showed mild cerebellar atrophy and increased signal intensity of bilateral inferior olivary nuclei on T2-weighted image. progressive ataxia and palatal tremor (PAPT) has recently been described as a rare sporadic neurodegenerative disease and the features of our case consistent with those of PAPT. However, for correct diagnosis of PAPT, multiple system atrophy, spinocerebellar ataxia, progressive supranuclear palsy or adult-onset Alexander's disease should be carefully ruled out.

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.

Central nervous system neuronal surface antibody associated syndromes: review and guidelines for recognition

The concept of antibody mediated CNS disorders is relatively recent. The classical CNS paraneoplastic neurological syndromes are thought to be T cell mediated, and the onconeural antibodies merely biomarkers for the presence of the tumour. Thus it was thought that antibodies rarely, if ever, cause CNS disease. Over the past 10 years, identification of autoimmune forms of encephalitis with antibodies against neuronal surface antigens, particularly the voltage gated potassium channel complex proteins or the glutamate N-methyl-D-aspartate receptor, have shown that CNS disorders, often without associated tumours, can be antibody mediated and benefit from immunomodulatory therapies. The clinical spectrum of these diseases is not yet fully explored, there may be others yet to be discovered and some types of more common disorders (eg, epilepsy or psychosis) may prove to have an autoimmune basis. Here, the known conditions associated with neuronal surface antibodies are briefly reviewed, some general aspects of these syndromes are considered and guidelines that could help in the recognition of further disorders are suggested.

Stiff-person syndrome (SPS) and anti-GAD-related CNS degenerations: protean additions to the autoimmune central neuropathies

Stiff Person Syndrome (SPS) is a rare autoimmune neurological disease attributable to autoantibodies to glutamic acid decarboxylase (anti-GAD) more usually associated with the islet beta cell destruction of autoimmune type 1 diabetes (T1D). SPS is characterized by interference in neurons with the synthesis/activity of the inhibitory neurotransmitter gamma amino butyric acid (GABA) resulting in the prototypic progressive spasmodic muscular rigidity of SPS, or diverse neurological syndromes, cerebellar ataxia, intractable epilepsy, myoclonus and several others. Remarkably, a single autoantibody, anti-GAD, can be common to widely different disease expressions, i.e. T1D and SPS. One explanation for these data is the differences in epitope engagement between the anti-GAD reactivity in SPS and T1D: in both diseases, anti-GAD antibody reactivity is predominantly to a conformational epitope region in the PLP- and C-terminal domains of the 65 kDa isoform but, additionally in SPS, there is reactivity to conformational epitope(s) on GAD67, and short linear epitopes in the C-terminal region and at the N-terminus of GAD65. Another explanation for disease expressions in SPS includes ready access of anti-GAD to antigen sites due to immune responsiveness within the CNS itself according to intrathecal anti-GAD-specific B cells and autoantibody. Closer study of the mysterious stiff-person syndrome should enhance the understanding of this disease itself, and autoimmunity in general.

[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.

Opsoclonus-myoclonus-ataxia syndrome with autoantibodies to glutamic acid decarboxylase

Opsoclonus-myoclonus-ataxia syndrome (OMS) is a rare neurological disorder of probably autoimmune origin. Most cases are associated with a remote neoplasm or a viral infection; however in some instances no underlying aetiology can be demonstrated. We report the presence of anti-glutamic acid decarboxylase antibodies (anti-GAD Abs) in the serum and CSF of a patient with idiopathic OMS. Treatment with intravenous immunoglobulin led to a remarkable clinical improvement with parallel reduction of anti-GAD titers. Anti-GAD Abs have been associated with several neurological syndromes. They could also be responsible for the clinical triad of OMS, by impairing GABAergic transmission in specific brainstem and cerebellar circuits. We propose that testing for anti-GAD Abs should be performed in OMS, especially when no other aetiological association can be demonstrated.

Rigidity and spasms from autoimmune encephalomyelopathies: stiff-person syndrome

Stiff-person syndrome (SPS) is a disorder characterized by progressive muscle rigidity with superimposed painful muscle spasms and gait impairment due to continuous motor activity. Evidence has accumulated in favor of SPS representing an autoimmune, predominantly encephalomyelopathic disorder resulting from B-cell-mediated clonal production of autoantibodies against presynaptic inhibitory epitopes on the enzyme glutamic acid decarboxylase (GAD) and the synaptic membrane protein amphiphysin. Recognition of the clinical spectrum of SPS is important, particularly the upper-limb, cervical, and cranial nerve involvement that occurs in paraneoplastic variants. The correlation between antibody levels and severity of disease offers evidence for a pathogenic role for the anti-GAD and anti-amphiphysin autoantibodies. The scarcity of neuropathological correlates stand in sharp contrast with the severity of the disability in affected individuals and suggests that functional impairment of inhibitory circuits without structural damage is sufficient to develop the full clinical spectrum of SPS. The rarity of this condition limits the feasibility of controlled clinical trials in the treatment of SPS, but the available evidence suggest that drugs that increase cortical and spinal inhibition such as benzodiazepines and drugs that provide immune modulation such as intravenous immunoglobulin, plasmapheresis, and prednisone are effective treatments.

Anti-GAD antibody cerebellar ataxia mimicking Creutzfeldt–Jakob disease

In a patient with a rapidly progressive neurological condition with ataxia and cognitive complaints, Creutzfeldt-Jakob disease (CJD) is often high in the differential, particularly when there is an elevated CSF 14-3-3 protein level. We present a case of anti-glutamic acid decarboxylase antibody (anti-GAD65) positive cerebellar ataxia associated with cognitive complaints and elevated CSF 14-3-3 protein.

Analysis of GAD65 autoantibodies in Stiff-Person syndrome patients

Autoantibodies to the 65-kDa isoform of glutamate decarboxylase GAD65 (GAD65Ab) are strong candidates for a pathological role in Stiff-Person syndrome (SPS). We have analyzed the binding specificity of the GAD65Ab in serum and cerebrospinal fluid (CSF) of 12 patients with SPS by competitive displacement studies with GAD65-specific rFab-derived from a number of human and mouse mAbs specific for different determinants on the Ag. We demonstrate considerable differences in the epitope specificity when comparing paired serum and CSF samples, suggesting local stimulation of B cells in the CSF compartment of these patients. Moreover, these autoantibodies strongly inhibit the enzymatic activity of GAD65, thus blocking the formation of the neurotransmitter gamma-aminobutyric acid. The capacity of the sera to inhibit the enzymatic activity of GAD65 correlated with their binding to a conformational C-terminal Ab epitope. Investigation of the inhibitory mechanism revealed that the inhibition could not be overcome by high concentrations of glutamate or the cofactor pyridoxal phosphate, suggesting a noncompetitive inhibitory mechanism. Finally, we identified a linear epitope on amino acids residues 4-22 of GAD65 that was recognized solely by autoantibodies from patients with SPS but not by serum from type 1 diabetes patients. A mAb (N-GAD65 mAb) recognizing this N-terminal epitope was successfully humanized to enhance its potential therapeutic value by reducing its overall immunogenicity.

Type 1 diabetes mellitus and drug-resistant epilepsy: presence of high titer of anti-glutamic acid decarboxylase autoantibodies in serum and cerebrospinal fluid

A 55-year-old man who was diagnosed as having type 1 diabetes mellitus (DM) at the age of 50 years was started on insulin therapy. At 54 years old of age, he suddenly developed complex partial seizures, which frequently occurred despite intensive anti-epileptic drug therapy. Neurological examination on admission revealed hyporeflexia in bilateral upper and lower extremities without any muscle rigidity, painful spasm or cerebellar ataxia. Laboratory examination showed poor glycemic control with increased glycated hemoglobin levels. Positive anti-thyroglobulin antibodies and anti-thyroid peroxidase (TPO) antibodies and slight elevation of TSH levels are consistent with subclinical hypothyroidism due to Hashimoto's thyroiditis. A high titer of anti-glutamic acid decarboxylase (GAD) antibodies was detected in the patient's serum and cerebrospinal fluid (CSF). Electroencephalography showed temporal spikes, consistent with complex partial seizure. This is a very rare case presenting with concomitant type 1 diabetes and drug-resistant epilepsy associated with high titers of circulating and CSF anti-GAD antibodies.

No association of anti-GM1 and anti-GAD antibodies with juvenile myoclonic epilepsy: A pilot study

PURPOSE

The presence of anti-ganglioside (GM1) or anti-glutamic acid decarboxylase (GAD) antibodies has been reported in association with therapy-resistant epilepsy mostly of focal origin. Our aim was to detect GM1 and GAD autoantibodies in patients with juvenile myoclonic epilepsy (JME) and to evaluate their association with rarely encountered therapy-resistant cases in this idiopathic generalised epilepsy syndrome.

METHODS

Ninety-six consecutive JME patients and 25 healthy normal control subjects were included to the study. We investigated anti-GM1 and anti-GAD antibodies with enzyme-linked immunosorbent assay (ELISA) and radioimmunoassay (RIA), respectively.

RESULTS

We found anti-GM1 antibodies in one of 96 (1.04%) JME patients and in one out of 25 (4%) healthy controls, without reaching a significant difference between the titres. Anti-GAD antibodies were detected in 5.8% of the patients and in 4% of the healthy controls. Both antibodies did not have any association with therapy-resistant cases and with any other relevant parameters.

CONCLUSIONS

The results of our pilot study suggested that anti-GM1 and anti-GAD antibodies are rare and they did not associate with therapy-resistance and other parameters in JME syndrome.

Antigenic differences between neurological and diabetic patients with anti-glutamic acid decarboxylase antibodies

Antibodies to glutamic acid decarboxylase (GADAb) are found in Stiff-Person syndrome, type 1 diabetes, cerebellar ataxia and other neurological disorders (such as epilepsy and myoclonus) involving the GABAergic ways. GADAb are usually detected by immunohistochemistry (IHC), radioimmunoassay (RIA) or enzyme-linked immunosorbent assay (ELISA). This study analysed the serum of 14 patients with neurological disorders who were positive by IHC for GADAb. The performance of a commercial RIA was compared with in-house immunoblotting and ELISA methods using recombinant GAD65 (rGAD65). RIA was positive in 14 of 14, immunoblotting was positive in seven of 14 and ELISA in 12 of 14. There was no correlation between the RIA result and the ELISA optical densities. Using a sodium thiocyanate chaotrope system with ELISA to determine antibody affinity, we found no significant correlation between antibody affinity and the RIA result. A consensus should be defined concerning which assay could be used as the gold standard for detecting GADAb. The most intriguing finding was that GAD antibodies from uncomplicated diabetics do not appear to recognize GAD in frozen sections from the rat cerebellum, whereas GAD antibodies from neurologically compromised diabetics do. A working proposal is therefore that type 1 diabetic patients with unusual neurological symptoms should be tested for GADAb both by RIA and IHC.

The spectrum of antineuronal autoantibodies in a series of neurological patients

The aim of the present study is to identify the range of neurological disorders expressing antineuronal antibodies, evaluate the number of different patterns of reactivity that can be detected, and analyse the contribution of these studies to the identification of subgroups of patients. The records of 882 patients were reviewed and their sera and cerebrospinal fluids tested for antineuronal antibodies. Patients were initially divided into four groups according to suspected clinical diagnosis. Autoantibodies were detected by immunohistochemistry, Western blot of gradient-separated neuronal and recombinant proteins and by RIA. Cerebellar degeneration and sensory neuropathies were the most common neurological disorders in which paraneoplastic-related anti-neuronal antibodies were detected. However, in addition to PCA1/anti-Yo and ANNA1/anti-Hu antibodies, we found other reactivities in six patients with cerebellar degeneration: anti-GAD in three females and atypical in the other cases. The widest range of different anti-neuronal antibodies was detected in patients with peripheral sensory neuropathy. Few patients with Stiff-Person syndrome, temporal lobe epilepsy and myoclonus harboured anti-GAD antibodies. Atypical antibodies were detected in single cases with motor neuron disorder and multiple system atrophy. No anti-neuronal antibodies were detected in patients with neurological complications of connective tissue disorders other than Sjögren's syndrome, or in neurological diseases other than motor neuron disease and multiple system atrophy. Our study shows that the spectrum of neurological disorders in which anti-neuronal antibodies can be detected is wider than previously thought. In addition, we found patterns of neuronal staining and Western blot reactivity that differed from those so far reported. This may permit identification of subgroups of patients in whom strategies directed at removing and/or suppressing antibody production could be of some benefit.

Stiff-Person Syndrome

BACKGROUND

Stiff-person syndrome (SPS) is a rare neurologic disorder with autoimmune features. It is characterized by progressive, severe muscle rigidity or stiffness most prominently affecting the spine and lower extremities.

REVIEW SUMMARY

Superimposed muscle spasms result in simultaneous contraction of agonist and antagonist muscles which are detectable by electromyography (EMG) and relieved by administration of benzodiazepines. The exacerbation of SPS by emotional stressors often results in the referral of these patients for psychiatric assessment although this was more common before the discovery of an association with antibodies to glutamic acid decarboxylase (GAD antibodies). Formerly known as stiff-man syndrome, the female to male ratio is 2:1 and the principle paraneoplastic variant is associated with breast cancer. Although rare, this is a disease of middle age that severely curtails the functional capacity of those it strikes. It is frequently associated with diabetes and other autoimmune diseases. IVIg is recently demonstrated to be effective in the treatment of SPS; diazepam remains useful in managing the symptoms.

CONCLUSIONS

This article summarizes the history of SPS, describes important clinical features, discusses management, touches upon areas of uncertainty, and postulates some avenues for research.

Tremor of the mouth floor and anti-glutamic acid decarboxylase autoantibodies

Involuntary movements of the mouth can present as palatal tremor, which is frequently associated with hypertrophy of the inferior olivary nucleus and can be accompanied by contraction of other muscles of the head. We report the case of a 39-year-old man with autoimmune thyroiditis and diabetes who complained of involuntary rhythmic tremor involving the muscles of the floor of the mouth, which interfered with breathing and swallowing. Cerebrospinal fluid (CSF) examination showed the presence of oligoclonal bands and screening for anti-neuronal antibodies revealed high titres of anti-glutamic acid decarboxylase autoantibodies (GAD-Ab). Tremor responded to treatment with benzodiazepines. The correlation between the tremor and antibody positivity is unclear although an alteration of the gabaergic system mediated by the antibodies may be hypothesised on the basis of an inflammatory CSF profile.

Cerebellar ataxia associated with anti-glutamic acid decarboxylase autoantibodies

Recent reports describe the detection of high titres of antibodies to glutamic acid decarboxylase (GAD-Ab) in the serum and cerebrospinal fluid (CSF) of patients with cerebellar ataxia. Most of these cases are females with Polyglandular Autoimmune Disorder who develop a chronic cerebellar syndrome. The CSF profile is in keeping with an autoimmune disorder and intrathecal GAD-Ab synthesis has been demonstrated. The ataxia could reverse after immunomodulatory treatments suggesting a possible pathogenetic role for GAD-Ab.

Stiff man syndrome and related conditions

The stiff man syndrome (SMS) and its variants, focal SMS, stiff limb (or leg) syndrome (SLS), jerking SMS, and progressive encephalomyelitis with rigidity and myoclonus (PERM), appear to occur more frequently than hitherto thought. A characteristic ensemble of symptoms and signs allows a tentative clinical diagnosis. Supportive ancillary findings include (1) the demonstration of continuous muscle activity in trunk and proximal limb muscles despite attempted relaxation, (2) enhanced exteroceptive reflexes, and (3) antibodies to glutamic acid decarboxylase (GAD) in both serum and spinal fluid. Antibodies to GAD are not diagnostic or specific for SMS and the role of these autoantibodies in the pathogenesis of SMS/SLS/PERM is the subject of debate and difficult to reconcile on the basis of our present knowledge. Nevertheless, evidence is emerging to suggest that SMS/SLS/PERM are manifestations of an immune-mediated chronic encephalomyelitis and immunomodulation is an effective therapeutic approach.

Stiff-person syndrome: autoimmunity and the central nervous system

Stiff-person syndrome (SPS) is a rare disease of severe progressive muscle stiffness in the spine and lower extremities with superimposed muscle spasms triggered by external stimuli. Patients with SPS are often referred for psychiatric evaluation and the psychiatrist may be the first to diagnosis SPS. Psychosocial stressors often precede the first manifestations of the disease; depression, anxiety, and alcohol abuse are comorbid illnesses. The identification of an association with antibodies to glutamic acid decarboxylase (GAD) was invaluable for definitively establishing a pathological basis for the disease; antibodies to amphiphysin and gephyrin are also found in cases of SPS but at much lower frequencies. Whether the antibodies inhibit GAD activity in vivo, target GAD-expressing neurons for immune-mediated destruction, are part of a wider immune process, or are merely a marker for destruction of GAD-expressing neurons by an independent neurodegenerative process is not yet clear. Both electromyography and the detection of GAD antibodies are useful in establishing a diagnosis of SPS. Treatment of SPS includes the use of immunomodulating therapies (plasmapheresis and intravenous immunoglobulins) and symptomatic treatment with benzodiazepines and baclofen. The use of tricyclic antidepressants and rapid withdrawal from therapy should be avoided.