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

Cerebellar ataxia and autoantibodies restricted to glutamic acid decarboxylase 67 (GAD67)

Cerebellar ataxia is one of the most frequent syndromes associated with autoantibodies against glutamic acid decarboxylase (GAD-ab). Antibodies recognize the isoform GAD65, which is the standard biomarker, but additional immunoreactivity against GAD67 is found in high proportion of patients with GAD-ab-associated neurological disorders. We describe the case of a 59-year-old woman who presented with pancerebellar syndrome of subacute onset (9weeks to nadir). In the etiological study, high titers of GAD-ab were found, but these only recognized the GAD67 isoform and not the GAD65. Screening of GAD67-ab should be considered in late-onset cerebellar ataxia when GAD65-ab are absent.

Clinical and Immunological Features of Opsoclonus-Myoclonus Syndrome in the Era of Neuronal Cell Surface Antibodies

IMPORTANCE

Most studies on opsoclonus-myoclonus syndrome (OMS) in adults are based on small case series before the era of neuronal cell surface antibody discovery.

OBJECTIVE

To report the clinical and immunological features of idiopathic OMS (I-OMS) and paraneoplastic OMS (P-OMS), the occurrence of antibodies to cell surface antigens, and the discovery of a novel cell surface epitope.

DESIGN, SETTING, AND PARTICIPANTS

Retrospective cohort study and laboratory investigations of 114 adult patients with OMS at a center for autoimmune neurological disorders done between January 2013 and September 2015.

MAIN OUTCOMES AND MEASURES

Review of clinical records. Immunohistochemistry on rat brain and cultured neurons as well as cell-based assays were used to identify known autoantibodies. Immunoprecipitation and mass spectrometry were used to characterize novel antigens.

RESULTS

Of the 114 patients (62 [54%] female; median age, 45 years; interquartile range, 32-60 years), 45 (39%) had P-OMS and 69 (61%) had I-OMS. In patients with P-OMS, the associated tumors included lung cancer (n = 19), breast cancer (n = 10), other cancers (n = 5), and ovarian teratoma (n = 8); 3 additional patients without detectable cancer were considered to have P-OMS because they had positive results for onconeuronal antibodies. Patients with I-OMS, compared with those who had P-OMS, were younger (median age, 38 [interquartile range, 31-50] vs 54 [interquartile range, 45-65] years; P < .001), presented more often with prodromal symptoms or active infection (33% vs 13%; P = .02), less frequently had encephalopathy (10% vs 29%; P = .01), and had better outcome (defined by a modified Rankin Scale score ≤ 2 at last visit; 84% vs 39%; P < .001) with fewer relapses (7% vs 24%; P= .04). Onconeuronal antibodies occurred in 13 patients (11%), mostly Ri/ANNA2 antibodies, which were detected in 7 of 10 patients (70%) with breast cancer. Neuronal surface antibodies were identified in 12 patients (11%), mainly glycine receptor antibodies (9 cases), which predominated in P-OMS with lung cancer (21% vs 5% in patients with OMS without lung cancer; P = .02); however, a similar frequency of glycine receptor antibodies was found in patients with lung cancer without OMS (13 of 65 patients [20%]). A novel cell surface epitope, human natural killer 1 (HNK-1), was the target of the antibodies in 3 patients with lung cancer and P-OMS.

CONCLUSIONS AND RELEVANCE

Patients with I-OMS responded better to treatment and had fewer relapses than those with P-OMS. Older age and encephalopathy, significantly associated with P-OMS, are clinical clues suggesting an underlying tumor. Glycine receptor antibodies occur frequently in P-OMS with lung cancer, but the sensitivity and specificity are low. The HNK-1 epitope is a novel epitope in a subset of patients with P-OMS and lung cancer.

Consensus Paper: Neuroimmune Mechanisms of Cerebellar Ataxias

In the last few years, a lot of publications suggested that disabling cerebellar ataxias may develop through immune-mediated mechanisms. In this consensus paper, we discuss the clinical features of the main described immune-mediated cerebellar ataxias and address their presumed pathogenesis. Immune-mediated cerebellar ataxias include cerebellar ataxia associated with anti-GAD antibodies, the cerebellar type of Hashimoto's encephalopathy, primary autoimmune cerebellar ataxia, gluten ataxia, Miller Fisher syndrome, ataxia associated with systemic lupus erythematosus, and paraneoplastic cerebellar degeneration. Humoral mechanisms, cell-mediated immunity, inflammation, and vascular injuries contribute to the cerebellar deficits in immune-mediated cerebellar ataxias.

Neuronal central nervous system syndromes probably mediated by autoantibodies

In the last few years, a rapidly growing number of autoantibodies targeting neuronal cell-surface antigens have been identified in patients presenting with neurological symptoms. Targeted antigens include ionotropic receptors such as N-methyl-d-aspartate receptor or the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor, metabotropic receptors such as mGluR1 and mGluR5, and other synaptic proteins, some of them belonging to the voltage-gated potassium channel complex. Importantly, the cell-surface location of these antigens makes them vulnerable to direct antibody-mediated modulation. Some of these autoantibodies, generally targeting ionotropic channels or their partner proteins, define clinical syndromes resembling models of pharmacological or genetic disruption of the corresponding antigen, suggesting a direct pathogenic role of the associated autoantibodies. Moreover, the associated neurological symptoms are usually immunotherapy-responsive, further arguing for a pathogenic effect of the antibodies. Some studies have shown that some patients' antibodies may have structural and functional in vitro effects on the targeted antigens. Definite proof of the pathogenicity of these autoantibodies has been obtained for just a few through passive transfer experiments in animal models. In this review we present existing and converging evidence suggesting a pathogenic role of some autoantibodies directed against neuronal cell-surface antigens observed in patients with central nervous system disorders. We describe the main clinical symptoms characterizing the patients and discuss conflicting arguments regarding the pathogenicity of these antibodies.

Clinical Spectrum of Stiff Person Syndrome: A Review of Recent Reports

Background

“Classic” stiff person syndrome (SPS) features stiffness, anti-glutamic acid decarboxylase (anti-GAD) antibodies, and other findings. Anti-GAD antibodies are also detected in some neurological syndromes (such as ataxia) in which stiffness is inconsistently present. Patients with otherwise “classic” SPS may either lack anti-GAD antibodies or be seropositive for others. Hence, SPS cases appear to fall within a clinical spectrum that includes conditions such as progressive encephalomyelitis with rigidity and myoclonus (PERM), which exhibits brainstem and autonomic features. We have compiled herein SPS-spectrum cases reported since 2010, and have segregated them on the basis of likely disease mechanism (autoimmune, paraneoplastic, or cryptogenic) for analysis.

Methods

The phrases “stiff person syndrome”, “PERM”, “anti-GAD antibody syndrome”, and “glycine receptor antibody neurological disorders” were searched for in PubMed in January 2015. The results were narrowed to 72 citations after excluding non-English and duplicate reports. Clinical descriptions, laboratory data, management, and outcomes were categorized, tabulated, and analyzed.

Results

Sixty-nine autoimmune, 19 paraneoplastic, and 13 cryptogenic SPS-spectrum cases were identified. SPS was the predominant diagnosis among the groups. Roughly two-thirds of autoimmune and paraneoplastic cases were female. Anti-GAD antibodies were most frequently identified, followed by anti-amphiphysin among paraneoplastic cases and by anti-glycine receptor antibodies among autoimmune cases. Benzodiazepines were the most commonly used medications. Prognosis seemed best for cryptogenic cases; malignancy worsened that of paraneoplastic cases.

Discussion

Grouping SPS-spectrum cases by pathophysiology provided insights into work-up, treatment, and prognosis. Ample phenotypic and serologic variations are present within the categories. Ruling out malignancy and autoimmunity is appropriate for suspected SPS-spectrum cases.

Paraneoplastic disorders

PURPOSE OF REVIEW

Paraneoplastic disorders are autoimmune diseases associated with risks for specific cancers and marked by specific autoantibodies. They cause diverse clinical syndromes of the central and peripheral nervous systems.

RECENT FINDINGS

In the peripheral nervous system, autoimmunity to synaptic or axonal proteins has long been recognized to associate with specific cancers. In these disorders, typified by myasthenia gravis, the antibodies are directly toxic, and recovery with immunotherapy is the rule. In contrast, the classic paraneoplastic syndromes involve a higher risk of cancer, autoantibodies to intracellular proteins (eg, Hu proteins), T-cell-dependent disease mechanisms targeting the CNS or peripheral nervous system, and a poor response to treatment. Following the discovery of N-methyl-D-aspartate (NMDA) receptor antibodies, a new and expanding group of disorders involving autoantibodies to CNS synaptic and neuronal membrane proteins and a favorable response to immunotherapy emerged. A final group of disorders involves antibodies to intracellular synaptic proteins, such as glutamic acid decarboxylase 65 (GAD65), and it is unclear whether these diseases involve antibody or T-cell mechanisms.

SUMMARY

Neurologists should recognize the clinical syndromes associated with paraneoplastic disorders, utilize autoantibody and other testing to confirm the diagnosis, understand the pathologic basis of the diseases, and promptly give appropriate therapies.

Paraneoplastic and idiopathic autoimmune neurologic disorders: approach to diagnosis and treatment

Autoimmune neurology is a rapidly emerging new subspecialty that encompasses the diagnosis and treatment of neurologic disorders with an autoimmune (paraneoplastic or noncancer-associated) basis. The last decade has seen a dramatic rise in the discovery of neural-specific autoantibodies and their target antigens. Laboratory testing, on a service basis, is now available for most of these neural-specific autoantibodies and they serve as diagnostic markers, in some instances directing the physician toward specific cancer types (e.g., N-methyl-d-aspartate receptor antibodies for teratoma; CRMP5-IgG for small-cell cancer) and assisting in therapeutic decision making. Antibodies targeting intracellular proteins (nuclear and intracytoplasmic enzymes, transcription factors, and RNA binding proteins) serve as markers of cytotoxic effector T-cell-mediated injury and are generally poorly responsive to immunotherapy. By contrast, antibodies targeting plasma membrane proteins that are extracellular and accessible (neurotransmitter receptors, ion channels, water channels, and channel-complex proteins) may act as pathogenic effectors and often imply immunotherapy responsiveness. Magnetic resonance imaging, electrophysiologic studies, functional imaging, and neuropsychologic evaluations provide objective evidence of neurologic dysfunction by which the success of immunotherapy may be measured.

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

Autoantibodies to glutamic acid decarboxylase (Gad-Abs) are implicated in various neurological syndromes. The present study aims to identify intrathecal-specific GAD-Abs and to determine clinical manifestations and treatment outcomes. Nineteen patients had GAD-Abs in cerebrospinal fluid but not in paired serum samples. Neurological syndromes included limbic encephalitis, temporal lobe epilepsy, cerebellar ataxia, autonomic dysfunction, and stiff-person syndrome. Immunotherapy had beneficial effects in 57.1% of patients, and the patients with limbic encephalitis responded especially well to immunotherapy. Intrathecal-specific antibodies to GAD at low titers may appear as nonspecific markers of immune activation within the central nervous system rather than pathogenic antibodies causing neuronal dysfunction.

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.

Paraneoplastic Neurological Syndromes and Glutamic Acid Decarboxylase Antibodies

IMPORTANCE

Little is known of glutamic acid decarboxylase antibodies (GAD-abs) in the paraneoplastic context. Clinical recognition of such cases will lead to prompt tumor diagnosis and appropriate treatment.

OBJECTIVE

To report the clinical and immunological features of patients with paraneoplastic neurological syndromes (PNS) and GAD-abs.

DESIGN, SETTING, AND PARTICIPANTS

Retrospective case series study and immunological investigations conducted in February 2014 in a center for autoimmune neurological disorders. Fifteen cases with GAD65-abs evaluated between 1995 and 2013 who fulfilled criteria of definite or possible PNS without concomitant onconeural antibodies were included in this study.

MAIN OUTCOMES AND MEASURES

Analysis of the clinical records of 15 patients and review of 19 previously reported cases. Indirect immunofluorescence with rat hippocampal neuronal cultures and cell-based assays with known neuronal cell-surface antigens were used. One hundred six patients with GAD65-abs and no cancer served as control individuals.

RESULTS

Eight of the 15 patients with cancer presented as classic paraneoplastic syndromes (5 limbic encephalitis, 1 paraneoplastic encephalomyelitis, 1 paraneoplastic cerebellar degeneration, and 1 opsoclonus-myoclonus syndrome). When compared with the 106 non-PNS cases, those with PNS were older (median age, 60 years vs 48 years; P = .03), more frequently male (60% vs 13%; P < .001), and had more often coexisting neuronal cell-surface antibodies, mainly against γ-aminobutyric acid receptors (53% vs 11%; P < .001). The tumors more frequently involved were lung (n = 6) and thymic neoplasms (n = 4). The risk for an underlying tumor was higher if the presentation was a classic PNS, if it was different from stiff-person syndrome or cerebellar ataxia (odds ratio, 10.5; 95% CI, 3.2-34.5), or if the patient had coexisting neuronal cell-surface antibodies (odds ratio, 6.8; 95% CI, 1.1-40.5). Compared with the current series, the 19 previously reported cases had more frequent stiff-person syndrome (74% vs 13%; P = .001) and better responses to treatment (79% vs 27%; P = .005). Predictors of improvement in the 34 patients (current and previously reported) included presentation with stiff-person syndrome and the presence of a thymic tumor.

CONCLUSIONS AND RELEVANCE

Patients with GAD-abs must be screened for an underlying cancer if they have clinical presentations different from those typically associated with this autoimmunity or develop classic PNS. The risk for cancer increases with age, male sex, and the presence of coexisting neuronal cell-surface antibodies.

Long latency between GAD-antibody detection and development of limbic encephalitis--a case report

BACKGROUND

In the pathogenesis of limbic encephalitis other promoting factors besides the pure existence of autoantibodies are increasingly discussed to play a significant role. This is to our knowledge the first described patient in whom the presence of autoantibodies precedes the manifestation of limbic encephalitis for many years.

CASE PRESENTATION

At the age of 38 years, in the serum of a patient with polyendocrine autoimmunity high titers of cytoplasmic islet cell antibodies and of anti-glutamate decarboxylase (GAD) 65 antibodies were observed as an incidential finding, GAD67 antibodies were negative at that time. After a latency of 18 years, she manifested with refractory temporal lobe epilepsy most likely due to autoimmune limbic encephalitis. After epilepsy onset, the patient underwent magnetic resonance imaging (MRI), electroencephalography, cerebrospinal fluid (CSF), serum and neuropsychological investigations during a follow-up period of 8 years. A pharmacoresistent epilepsy with seizure onset from the right temporal lobe and declarative memory deficits were observed affecting primarily the recall of verbal informations. MRI showed a slightly increased signal in the right amygdala without progression. GAD antibodies could be detected in serum (titre 1: 1000) and CSF (titre 1:1) by immunofluorescence. Both, GAD65 and GAD67 antibodies were observed in cell-based assays.

CONCLUSIONS

It can be assumed that in addition to a pre-existing systemic T-cell response associated with the longstanding polyendocrine autoimmunity, a delayed intrathecal autoimmunity developed leading to limbic encephalitis. This change might be reflected by the development of GAD67 antibodies in our patient. Besides the contribution of this case report to a better understandig of the pathomechanisms for the development of central nervous system (CNS) autoimmunity, it also has a clinical impact as early treatment of GAD antibody-associated CNS disorders has a better prognosis. Therefore, vigilance for symptoms indicating GAD antibody-associated CNS autoimmunity is mandatory in patients with GAD antibody-associated endocrine dysfunction.

Multiple system atrophy-mimicking conditions: Diagnostic challenges

Multiple system atrophy (MSA) is a relentless progressive disorder without effective treatment. Its accurate diagnosis is important for the management of individual patients and for the development of new therapeutic strategies. However, there are many disorders which can mimic MSA (so-called 'MSA look-alikes'), and the true rate for over- or under-diagnoses of MSA is not known, especially during the early course of disease when the disease is not fully developed yet. Herein, the authors review the neurodegenerative, genetic, and immunologic conditions that can mimic MSA and thus be part of the differential diagnosis of MSA. Clinicians should be aware of these conditions and be able to differentiate them by clinical features and laboratory findings.

Primary and secondary ataxias

PURPOSE OF REVIEW

This article discusses recent advances in the understanding of clinical and genetic aspects of primary ataxias, including congenital, autosomal recessive, autosomal dominant, episodic, X-linked, and mitochondrial ataxias, as well as idiopathic degenerative and secondary ataxias.

RECENT FINDINGS

Many important observations have been published in recent years in connection with primary ataxias, particularly new loci and genes. The most commonly inherited ataxias may present with typical and atypical phenotypes. In the group of idiopathic degenerative ataxias, genes have been found in patients with multiple system atrophy type C. Secondary ataxias represent an important group of sporadic, cerebellar, and afferent/sensory ataxias.

SUMMARY

Knowledge of primary ataxias has been growing rapidly in recent years. Here we review different forms of primary ataxia, including inherited forms, which are subdivided into congenital, autosomal recessive cerebellar ataxias, autosomal dominant cerebellar ataxias, episodic ataxias, X-linked ataxias, and mitochondrial ataxias, as well as sporadic ataxias and idiopathic degenerative ataxias. Secondary or acquired ataxias are also reviewed and the most common causes are discussed.

Treatment of immune-mediated temporal lobe epilepsy with GAD antibodies

PURPOSE

Temporal lobe epilepsy with antibodies (abs) against the glutamic acid decarboxylase 65 isoform (GAD-TLE) is known as an immune-mediated neurological syndrome. Here we evaluate the therapy response to various immunotherapies and epilepsy surgery in this syndrome.

METHOD

All patients with GAD-TLE and follow-up data and stored serum and CSF samples, identified and treated at the Bonn centre from 2002 to 2010, were studied retrospectively. Seizure freedom for ≥1 year and reduction of ≥50%, i.e. therapy response, were assessed. GAD-ab titres and neuropsychological performances were documented prior and after individual interventions.

RESULTS

Thirteen patients with GAD-TLE were identified with the following seizure responses: corticosteroids (5 responders out of 11 treated patients); i.v. immunoglobulins (1/5), apheresis therapy (1/8); and natalizumab (1/1), selective amygdala-hippocampectomy (2/3). None of the patients achieved sustained seizure freedom apart from one patient. This patient was on antiepileptic drug treatment after discontinuation of immunotherapy.

CONCLUSION

The seizure response to immunotherapies in patients with GAD-TLE was poor. Corticosteroids were the most effective regarding seizure response. Especially the poor effects of apheresis therapies support the idea that GAD-abs are not directly pathogenic. None of three patients was seizure-free after temporal lobe surgery suggesting that GAD-TLE patients respond worse than others to this type of intervention. Our results reflect the chronic course of the disease with low likelihood for patients with GAD-TLE to attain long-term seizure freedom.

Antibodies to aquaporin 4, myelin-oligodendrocyte glycoprotein, and the glycine receptor α1 subunit in patients with isolated optic neuritis

IMPORTANCE

In patients with isolated optic neuritis (ON), the presence of antibodies to aquaporin 4 (AQP4) has diagnostic and prognostic value. In the same clinical setting, the significance of antibodies to myelin-oligodendrocyte glycoprotein (MOG) or the glycine receptor α1 subunit (GlyR) is unclear.

OBJECTIVES

To investigate the frequency of antibodies to AQP4, MOG, and GlyR in patients with unilateral or bilateral, severe, or recurrent isolated ON and to determine their clinical and prognostic correlates.

DESIGN, SETTING, AND PARTICIPANTS

Retrospective case-control study from November 1, 2005, through May 30, 2014 with the detection of autoantibodies in a neuroimmunology referral center. We included 51 patients with ON but without clinical and magnetic resonance imaging findings outside the optic nerves and 142 controls (30 healthy individuals, 48 patients with neuromyelitis optica, and 64 patients with multiple sclerosis).

MAIN OUTCOMES AND MEASURES

Clinicoimmunologic analysis. We determined the presence of antibodies to AQP4, MOG, and GlyR using cell-based assays.

RESULTS

The median age of the patients at the onset of ON symptoms was 28 (range, 5-65) years; 36 patients (71%) were female. Antibodies were identified in 23 patients (45%), including MOG in 10 patients, AQP4 in 6 patients, and GlyR in 7 patients (concurrent with MOG in 3 and concurrent with AQP4 in 1). Patients with AQP4 antibodies (median visual score, 3.5 [range, 1-9]) had a worse visual outcome than patients with MOG antibodies alone (median visual score, 0 [range, 0-5]; P = .007), patients with seronegative findings (n = 28) (median visual score, 1.0 [range, 0-14]; P = .08), and patients with GlyR antibodies alone (n = 3) (median visual score, 0 [range, 0-2]; P = .10).The median age of the 7 patients with GlyR antibodies was 27 (range, 11-38) years; 5 (71%) of these were female. Among the 3 patients with GlyR antibodies alone, 1 patient had monophasic ON, 1 had recurrent isolated ON, and 1 had conversion to multiple sclerosis. The 3 patients with GlyR antibodies concurrent with MOG antibodies had recurrent isolated ON, and the patient with concurrent AQP4 antibodies had conversion to neuromyelitis optica. Of the 48 controls with neuromyelitis optica, 37 (77%) had AQP4 antibodies, 4 (8%) had MOG antibodies, 2 (4%) had AQP4 antibodies concurrent with MOG antibodies, and 5 (10%) were seronegative. Of the 64 controls with multiple sclerosis, 5 (8%) had GlyR antibodies.

CONCLUSIONS AND RELEVANCE

Forty-five percent of patients with unilateral or bilateral, severe, or recurrent isolated ON had antibodies to MOG, AQP4, or GlyR. Patients with AQP4 antibodies had the poorest visual outcomes, whereas patients with MOG antibodies had a better outcome that was similar to that of patients with seronegative findings. The significance of GlyR antibodies in the setting of ON is unclear and deserves further study.

Antibodies to inhibitory synaptic proteins in neurological syndromes associated with glutamic acid decarboxylase autoimmunity

Antibodies to glutamic acid decarboxylase (GAD-ab) associate to different neurological syndromes. It is unknown if the diversity in syndrome association represents epitopes in different immunodominant domains or co-existence of antibodies to other proteins of the inhibitory synapsis. We examined the serum and CSF of 106 patients with anti-GAD related syndromes (39 cerebellar ataxia, 32 stiff-person syndrome [SPS], 18 epilepsy, and 17 limbic encephalitis [LE]). GAD65-ab titres were quantified by ELISA. Immunoblot was used to determine if the antibody-targeted epitopes of GAD65 and GAD67 were linear. A cell-based assay (CBA) with HEK293 cells expressing the GAD65 N-terminal, central catalytic domain, or C-terminal was used to investigate the immunodominant domains. Antibodies to GAD67, gamma-aminobutyric acid A receptor (GABAaR), glycine receptor (GlyR), GABAaR-associated protein (GABARAP), and gephyrin were determined with CBA. GAD-ab internalization was investigated using cultured rat hippocampal neurons. CSF GAD65-ab titres were higher in patients with cerebellar ataxia and LE compared to those with SPS (p = 0.02). GAD67-ab were identified in 81% of sera and 100% of CSF. GAD65-ab recognized linear epitopes in 98% of the patients and GAD67-ab in 42% (p<0.001). The GAD65 catalytic domain was recognized by 93% of sera, and the three domains by 22% of sera and 74% of CSF (p<0.001). Six patients had GABAaR-ab and another 6 had GlyR-ab without association to distinctive symptoms. None of the patients had gephyrin- or GABARAP-ab. GAD65-ab were not internalized by live neurons. Overall, these findings show that regardless of the neurological syndrome, the CSF immune response against GAD is more widespread than that of the serum and that there is no specific association between clinical phenotype and the presence of antibodies against other proteins of the inhibitory synapsis.

Treatable causes of cerebellar ataxia

The cerebellar ataxia syndromes are a heterogeneous group of disorders clinically characterized by the presence of cerebellar dysfunction. Initial assessment of patients with progressive cerebellar ataxia is complex because of an extensive list of potential diagnoses. A detailed history and comprehensive examination are required for an accurate diagnosis and hierarchical diagnostic investigations. Although no cure exists for most of these conditions, a small group of metabolic, hereditary, inflammatory, and immune-mediated etiologies of cerebellar ataxia are amenable to disease-modifying, targeted therapies. Over the past years, disease-specific treatments have emerged. Thus, clinicians must become familiar with these disorders because maximal therapeutic benefit is only possible when done early. In this article, we review disorders in which cerebellar ataxia is a prominent clinical feature requiring targeted treatments along with specific management recommendations.

GAD Antibody-Associated Late-Onset Cerebellar Ataxia in Two Female Siblings

Background

Anti-glutamic acid decarboxylase antibody (GAD-ab)-associated cerebellar ataxia is a rare neurological disorder characterized by cerebellar symptoms concomitant with high GAD-ab levels in serum and cerebrospinal fluid (CSF).

Case Report

We report on 2 female siblings (aged 74 and 76 years) presenting with gradual progression of rotational vertigo, gait ataxia and vertical diplopia, continuously progressing for 6 months and 6 years, respectively. Autoimmune laboratory examinations showed remarkably increased serum and CSF GAD-ab levels. Their medical histories revealed late-onset type 1 diabetes mellitus (T1DM) and other concomitant autoimmune disorders (Grave's disease, Hashimoto's thyroiditis). Cerebral MRI and laboratory examinations were unremarkable. The diagnosis of GAD-ab-associated cerebellar ataxia with particular brainstem involvement was established in both women. After the exclusion of an underlying malignancy, immunosuppressive therapy has been initiated in both patients, which resulted in stabilization in one and in clinical improvement in the other patient.

Discussion

The unique association of autoantibody-mediated cerebellar ataxia and late-onset T1DM in 2 siblings with similar clinical and paraclinical phenotypes strengthens the concept that hereditary factors might play a relevant role also in autoimmune diseases so far considered to be sporadic. Moreover, the occurrence of continuous vertical diplopia broadens the clinical spectrum of GAD-ab-associated neurological syndromes.