Ocular Motor and Vestibular Characteristics of Antiglutamic Acid Decarboxylase-Associated Neurologic Disorders

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.

An update on malignant tumor-related stiff person syndrome spectrum disorders: clinical mechanism, treatment, and outcomes

Stiff person syndrome (SPS) is a rare central nervous system disorder associated with malignancies. In this review, we retrieved information from PubMed, up until August 2023, using various search terms and their combinations, including SPS, stiff person syndrome spectrum disorders (SPSSDs), paraneoplastic, cancer, and malignant tumor. Data from peer-reviewed journals printed in English were organized to explain the possible relationships between different carcinomas and SPSSD subtypes, as well as related autoantigens. From literature searching, it was revealed that breast cancer was the most prevalent carcinoma linked to SPSSDs, followed by lung cancer and lymphoma. Furthermore, classic SPS was the most common SPSSD subtype, followed by stiff limb syndrome and progressive encephalomyelitis with rigidity and myoclonus. GAD65 was the most common autoantigen in patients with cancer and SPSSDs, followed by amphiphysin and GlyR. Patients with cancer subtypes might have multiple SPSSD subtypes, and conversely, patients with SPSSD subtypes might have multiple carcinoma subtypes. The first aim of this review was to highlight the complex nature of the relationships among cancers, autoantigens, and SPSSDs as new information in this field continues to be generated globally. The adoption of an open-minded approach to updating information on new cancer subtypes, autoantigens, and SPSSDs is recommended to renew our database. The second aim of this review was to discuss SPS animal models, which will help us to understand the mechanisms underlying the pathogenesis of SPS. In future, elucidating the relationship among cancers, autoantigens, and SPSSDs is critical for the early prediction of cancer and discovery of new therapeutic modalities.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Centripetal Nystagmus, Slow Saccades, Cerebellar Ataxia, and Parkinsonism in a Patient With Anti-GAD65-Associated Stiff Person Syndrome Spectrum Disorder

ABSTRACT

A 68-year-old woman with positional dizziness and progressive imbalance presented for vestibular evaluation. Examination was notable for spontaneous downbeat nystagmus (DBN), horizontal and vertical gaze-evoked nystagmus (GEN) with centripetal and rebound nystagmus, and positional apogeotropic nystagmus. There was also mild-moderate slowing of saccades horizontally and vertically and poor fast phases with an optokinetic stimulus. Further consultation by a movement disorder specialist uncovered asymmetric decrementing bradykinesia and rigidity, masked facies, and a wide-based stance without camptocormia. Screening serum laboratory results for metabolic, rheumatologic, infectious, heavy metal, endocrine, or vitamin abnormalities was normal. Surveillance imaging for neoplasms was unremarkable, and cerebrospinal fluid (CSF) analysis was negative for 14-3-3 and real-time quaking-induced conversion (RT-QuIC). However, her anti-glutamic acid decarboxylase-65 (GAD65) immunoglobulin G (IgG) level was markedly elevated in serum to 426,202 IU/mL (reference range 0-5 IU/mL) and in CSF to 18.1 nmol/L (reference range <0.03 nmol/L). No other autoantibodies were identified on the expanded paraneoplastic panel. The patient was referred to neuroimmunology, where torso rigidity, spasticity, and significant paravertebral muscle spasms were noted. Overall, the clinical presentation, examination findings, and extensive workup were consistent with a diagnosis of anti-GAD65-associated stiff person syndrome-plus (musculoskeletal plus cerebellar and/or brainstem involvement). She was subsequently treated with intravenous immunoglobulin (IVIg) and has been stable since commencing this therapy. In patients with centripetal nystagmus, especially in association with other cerebellar findings, an autoimmune cerebellar workup should be considered.

Stiff person syndrome spectrum disorders; more than meets the eye

Stiff person syndrome spectrum disorders (SPSD) are a group of rare neuroimmunological disorders that often include painful spasms and rigidity. However, patients have highly heterogeneous signs and symptoms which may reflect different mechanistic disease processes. Understanding subsets of patients based on clinical phenotype may be important for prognosis and guiding treatment. The goal of this review is to provide updates on SPSD and its expanding clinical spectrum, prognostic markers, and treatment considerations. Further, we describe the current understanding in immunopathogenesis and highlight gaps in our knowledge appropriate for future research directions. Examples of revised diagnostic criteria for SPSD based on phenotype are also presented.