Subcutaneous immunoglobulin for maintenance therapy in stiff-person syndrome: One-year follow-up in two patients

Stiff Person Syndrome and GAD Antibody-Spectrum Disorders

OBJECTIVE

Antibodies against glutamic acid decarboxylase (GAD), originally associated with stiff person syndrome (SPS), define the GAD antibody-spectrum disorders that also include cerebellar ataxia, autoimmune epilepsy, limbic encephalitis, progressive encephalomyelitis with rigidity and myoclonus (PERM), and eye movement disorders, all of which are characterized by autoimmune neuronal excitability. This article elaborates on the diagnostic criteria for SPS and SPS spectrum disorders, highlights disease mimics and misdiagnoses, describes the electrophysiologic mechanisms and underlying autoimmunity of stiffness and spasms, and provides a step-by-step therapeutic scheme.

LATEST DEVELOPMENTS

Very-high serum GAD antibody titers are diagnostic for GAD antibody-spectrum disorders and also predict the presence of GAD antibodies in the CSF, increased intrathecal synthesis, and reduced CSF γ-aminobutyric acid (GABA) levels. Low serum GAD antibody titers or the absence of antibodies generates diagnostic challenges that require careful distinction in patients with a variety of painful spasms and stiffness, including functional neurologic disorders. Antibodies against glycine receptors, first found in patients with PERM, are seen in 13% to 15% of patients with SPS, whereas amphiphysin and gephyrin antibodies, seen in 5% of patients with SPS spectrum disorders, predict a paraneoplastic association. GAD-IgG from different SPS spectrum disorders recognizes the same dominant GAD intracellular epitope and, although the pathogenicity is unclear, is an excellent diagnostic marker. The biological basis of muscle stiffness and spasms is related to autoimmune neuronal hyperexcitability caused by impaired reciprocal γ-aminobutyric acid-mediated (GABA-ergic) inhibition, which explains the therapeutic response to GABA-enhancing agents and immunotherapies.

ESSENTIAL POINTS

It is essential to distinguish SPS spectrum disorders from disease mimics to avoid both overdiagnoses and misdiagnoses, considering that SPS is treatable if managed correctly from the outset to prevent disease progression. A step-by-step, combination therapy of GABA-enhancing medications along with immunotherapies ensures prolonged clinical benefits.

Expanding clinical profiles and prognostic markers in stiff person syndrome spectrum disorders

OBJECTIVE

To describe the clinical features of a cohort of individuals with stiff person syndrome spectrum disorders (SPSD) and identify potential early predictors of future disability.

BACKGROUND

There is a need to better understand the full spectrum of clinical and paraclinical features and long-term impact of SPSD.

DESIGN/METHODS

Observational study from 1997 to 2022 at Johns Hopkins. Clinical phenotypes included classic SPS, partial SPS (limb or trunk limited), SPS-plus (classic features plus cerebellar/brainstem involvement), and progressive encephalomyelitis with rigidity and myoclonus (PERM). Outcome measures were modified Rankin scale (mRS) and use of assistive device for ambulation. Multivariate logistic regression was used to assess significant predictors of outcomes.

RESULTS

Cohort included 227 individuals with SPSD with mean follow-up of 10 years; 154 classic, 48 SPS-plus, 16 PERM, and 9 partial. Mean age at symptom onset was 42.9 ± 14.1 years, majority were white (69.2%) and female (75.8%). Median time to diagnosis was 36.2 months (longest for SPS-plus and PERM) and 61.2% were initially misdiagnosed. Most had systemic co-morbidities and required assistive devices for ambulation. Female sex (OR 2.08; CI 1.06-4.11) and initial brainstem/cerebellar involvement (OR 4.41; CI 1.63-14.33) predicted worse outcome by mRS. Older age at symptom onset (OR 1.04; CI 1.01-1.06), female sex (OR 1.99; CI 1.01-4.01), Black race (OR 4.14; CI 1.79-10.63), and initial brainstem/cerebellar involvement (OR 2.44; CI 1.04-7.19) predicted worse outcome by use of assistive device. Early implementation of immunotherapy was associated with better outcomes by either mRS (OR 0.45; CI 0.22-0.92) or use of assistive device (OR 0.79; CI 0.66-0.94).

CONCLUSIONS

We present the expanding phenotypic variability of this rare spectrum of disorders and highlight potential predictors of future disability.

Efgartigimod beyond myasthenia gravis: the role of FcRn-targeting therapies in stiff-person syndrome

Stiff-person syndrome (SPS) is a rare autoimmune neurological disorder characterized by high titers of antibodies against glutamic acid decarboxylase (GAD) causing impaired GABAergic inhibitory neurotransmission. To date, there is not a defined therapy for such condition, but immunomodulating therapies, such as plasma exchange, intravenous immunoglobulins, and rituximab, have been widely used in clinical practice. However, the efficacy and tolerability of these treatments is not well established. Efgartigimod, a new neonatal Fc receptor (FcRn) blocker, is a human IgG1 antibody Fc fragment engineered with increased affinity for FcRn binding, leading to a reduction in IgGs levels, including pathogenic IgG autoantibody showing promising results in neurological autoimmune disorders and has been approved for the treatment of AChR-seropositive generalized myasthenia gravis (MG). In this study, we report and describe the first data on treatment with efgartigimod in three patients affected by both AChR-seropositive generalized MG and anti-GAD-seropositive SPS. Patients were followed since the start of efgartigimod and for the whole treatment period (12 weeks). MG symptoms were assessed with the "MG activity of daily living score" and the Quantitative Myasthenia Gravis score, while SPS ones were assessed with the "SPS activity of daily living score"; muscle strength was assessed with the Medical Research Council Sum score; the overall disability from MG and SPS was assessed by the modified Rankin Scale. All patients showed an improvement in symptoms of both SPS and MG after 2 cycles of treatment. Our data suggest that efgartigimod may be considered as a candidate drug for SPS and other autoantibody-mediated neurological disorders.

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.

Subcutaneous Immunoglobulin Therapy with IgPro20 in Patients with Stiff Person Syndrome and Primary Immunodeficiency Disease

Stiff Person Syndrome (SPS), a rare autoimmune neurologic disorder characterized by fluctuating muscle spasms and rigidity, is mediated by autoantibodies to glutamic acid decarboxylase (GAD) antibodies. Symptoms of SPS have been shown to improve after administration of intravenous immunoglobulin (IVIG) however, there is a paucity of information regarding use of SCIg in SPS. Four patients with Stiff Person Syndrome were treated with SCIgPro20 for a period between 31 to 101 months. Most reactions were local and mild. All patients reported improvement in spasticity, and 2 patients reported improvement in seizure frequency. SCIgPro20 was well tolerated in patients with SPS and was associated with improvement in symptoms.