Limited Benefits Halt Enrollment in Hematopoietic Stem Cell Transplantation Trial for Stiff-Person Syndrome: Should There Be More to Come?

Successful Autologous Hematopoietic Stem Cell Transplant in Glycine Receptor Antibody-Positive Stiff Person Syndrome: A Case Report

BACKGROUND AND OBJECTIVES

To describe a case of glycine receptor (GlyR) antibody-positive stiff person syndrome (SPS) treated with autologous hematopoietic stem cell transplant (aHSCT).

METHODS

This was a multicenter collaboration for the treatment of a single patient who underwent aHSCT as part of a clinical trial (NCT00716066). To objectively assess the response to transplantation, several clinical outcome measures were evaluated pretransplant and up to 18 months post-transplant, including modified Rankin Score (mRS), stiffness index, Hauser Ambulation Score (HAS), hypersensitivity index, timed 25-foot walk, and Montreal Cognitive Assessment.

RESULTS

After transplant, the patient achieved sustained clinical improvement evidenced across various clinical scales, including mRS, stiffness index, HAS, and 25-foot walk time.

DISCUSSION

aHSCT represents a promising treatment option for SPS, including for GlyR-positive patients. In addition, this case represents the need to validate and standardize best clinical outcome measures for patients with SPS.

CLASSIFICATION OF EVIDENCE

Class IV; this is a single observational study without controls.

Overview of treatment strategies in paraneoplastic neurological syndromes

Treatment strategies in paraneoplastic neurological syndromes rely on the three pillars of tumor treatment, immunotherapy, and symptomatic treatment, the first one being by far the most important in the majority of patients and syndromes. Classically, antibodies against extracellular antigens are directly pathogenic, and patients with these syndromes are more responsive to immunomodulatory or immunosuppressive treatments than the ones with antibodies against intracellular targets. This chapter first discusses some general principles of tumor treatment and immunotherapy, followed by a closer look at specific treatment options for different clinical syndromes, focusing on symptomatic treatments.

Stiff Person Spectrum Disorders-An Update and Outlook on Clinical, Pathophysiological and Treatment Perspectives

Stiff person spectrum disorders (SPSD) are paradigm autoimmune movement disorders characterized by stiffness, spasms and hyperekplexia. Though rare, SPSD represent a not-to-miss diagnosis because of the associated disease burden and treatment implications. After decades as an enigmatic orphan disease, major advances in our understanding of the evolving spectrum of diseases have been made along with the identification of multiple associated autoantibodies. However, the most important recent developments relate to the recognition of a wider affection, beyond the classic core motor symptoms, and to further insights into immunomodulatory and symptomatic therapies. In this review, we summarize the recent literature on the clinical and paraclinical spectrum, current pathophysiological understanding, as well as current and possibly future therapeutic strategies.

Hematopoietic Stem Cell Transplantation for the Treatment of Autoimmune Neurological Diseases: An Update

Over the last two decades, haematopoietic stem cell transplantation (HSCT) has been explored as a potential therapeutic strategy for autoimmune diseases refractory to conventional treatments, including neurological disorders. Although both autologous (AHSCT) and allogeneic HSCT (allo-HSCT) were investigated, AHSCT was preferentially developed due to a more favourable safety profile compared to allo-HSCT. Multiple sclerosis (MS) represents the most frequent neurological indication for AHSCT, but increasing evidence on the potential effectiveness of transplant in other autoimmune neurological diseases is emerging, although with a risk-benefit ratio overall more uncertain than in MS. In the present work, the rationale for the use of HSCT in neurological diseases and the experimental models that prompted its clinical application will be briefly covered. Case series and prospective studies exploring the use of HSCT in autoimmune diseases other than MS will be discussed, covering both frequent and rare neurological disorders such as myasthenia gravis, myopathies, and stiff-person syndrome. Finally, an updated summary of ongoing and future studies focusing on this issue will be provided.

Long-term Effectiveness of IVIg Maintenance Therapy in 36 Patients With GAD Antibody–Positive Stiff-Person Syndrome

Background and Objectives

IVIg has been the preferred immunotherapy in stiff-person syndrome (SPS) based on a 3-month controlled trial, but whether it is also effective in inducing long-term benefits or arresting disease progression is unknown. The information is needed because SPS is a progressively disabling disease and IVIg is liberally used as chronic therapy without efficacy data. The present study explores the long-term effects of IVIg in the largest cohort of well-characterized patients with SPS followed by the same clinicians over 10 years.

Methods

Data of 36 patients (32 glutamic acid decarboxylase [GAD] positive), diagnosed and treated with monthly maintenance IVIg by the same neurologists, were analyzed. Response was assessed by physician-observed changes, patients' reports of symptom improvement, modified Rankin Scale (mRS) scores, and dependency trials evaluating symptom recurrence after stopping IVIg, prolonging infusion frequency, decreasing monthly dose, or wearing-off effects in between doses. Clinically meaningful long-term response was defined by improved mRS scores, improvement in physician-assessed stiffness, balance and gait, and functional decline with dependency trials.

Results

Twenty-four of 36 (67%) patients had clinically meaningful response over a median 40-month period. Patients with improved mRS scores by 1–2 points manifested improved gait, posture, balance and decreased stiffness, spasms, and startle response; some patients using a wheelchair and those ambulating with devices walked unassisted. In 25% of responders, treatment benefit was sustained for a 40-month median period, but in 29.1%, it declined over a 39-month period; 12.5% exhibited a conditioning effect. Three of 5 patients with cerebellar GAD-SPS variant also improved over time. The 12 patients who did not respond the first 3 months remained unresponsive even if IVIg continued for several months.

Discussion

This is a large study in 36 patients with SPS demonstrating that monthly maintenance IVIg therapy offers long-term benefits in 67% of patients for a median 3.3-year period. Because 29.1% experienced diminishing benefit over time due to disease progression, the study highlights the need for more effective therapies.

Stiff-person Syndrome and GAD Antibody-spectrum Disorders: GABAergic Neuronal Excitability, Immunopathogenesis and Update on Antibody Therapies

Although antibodies against Glutamic Acid Decarboxylase (GAD) were originally associated with Stiff Person Syndrome (SPS), they now denote the "GAD antibody-spectrum disorders (GAD-SD)" that include Cerebellar Ataxia, Autoimmune Epilepsy, Limbic Encephalitis, PERM and eye movement disorder. In spite of the unique clinical phenotype that each of these disorders has, there is significant overlapping symptomatology characterized by autoimmune neuronal excitability. In addition to GAD, three other autoantibodies, against glycine receptors, amphiphysin and gephyrin, are less frequently or rarely associated with SPS-SD. Very high serum anti-GAD antibody titers are a key diagnostic feature for all GAD-SD, commonly associated with the presence of GAD antibodies in the CSF, a reduced CSF GABA level and increased anti-GAD-specific IgG intrathecal synthesis denoting stimulation of B-cell clones in the CNS. Because anti-GAD antibodies from the various hyperexcitability syndromes recognize the same dominant GAD epitope, the clinical heterogeneity among GAD-SD patients remains unexplained. The paper highlights the biologic basis of autoimmune hyperexcitability connected with the phenomenon of reciprocal inhibition as the fundamental mechanism of the patients' muscle stiffness and spasms; addresses the importance of high-GAD antibody titers in diagnosis, pinpointing the diagnostic challenges in patients with low-GAD titers or their distinction from functional disorders; and discusses whether high GAD-antibodies are disease markers or pathogenic in the context of their association with reduced GABA level in the brain and CSF. Finally, it focuses on therapies providing details on symptomatic GABA-enhancing drugs and the currently available immunotherapies in a step-by-step approach. The prospects of future immunotherapeutic options with antibody therapies are also summarized.

GAD antibody-spectrum disorders: progress in clinical phenotypes, immunopathogenesis and therapeutic interventions

Antibodies against glutamic acid decarboxylase (GAD), originally linked to stiff person syndrome (SPS), now denote the "GAD antibody-spectrum disorders" (GAD-SD) that also include autoimmune epilepsy, limbic encephalitis, cerebellar ataxia and nystagmus with overlapping symptomatology highlighting autoimmune neuronal excitability disorders. The reasons for the clinical heterogeneity among GAD-antibody associated syndromes remain still unsettled, implicating variable susceptibility of GABAergic neurons to anti-GAD or other still unidentified autoantibodies. Although anti-GAD antibody titers do not correlate with clinical severity, very high serum titers, often associated with intrathecal synthesis of anti-GAD-specific IgG, point to in-situ effects of GAD or related autoantibodies within the central nervous system. It remains, however, uncertain what drives these antibodies, why they persist and whether they are disease markers or have pathogenic potential. The review, focused on these concerns, describes the widened clinical manifestations and overlapping features of all GAD-SD; addresses the importance of GAD antibody titers and potential significance of GAD epitopes; summarizes the biologic basis of autoimmune hyperexcitability; highlights the electrophysiological basis of reciprocal inhibition in muscle stiffness; and provides practical guidelines on symptomatic therapies with gamma-aminobutyric acid-enhancing drugs or various immunotherapies.