Prevalence of non-neurological autoantibodies and related comorbidities in stiff person spectrum disorders.

Background: Stiff Person Syndrome Spectrum Disorders (SPSD) are a group of rare neurological disorders that can present alongside other autoimmune conditions. However, not much is known about the breadth of non-neurological autoantibodies seen in SPSD nor the observed prevalence of co-existing autoimmune comorbidities and their impact on SPSD. Objective: This study aimed to investigate the prevalence of non-neurological autoantibodies and associated conditions in a large cohort of people with SPSD. Methods: A retrospective review of 205 patients with suspected/definitive SPSD seen at Johns Hopkins Hospital from 1997 to 2023 was performed as part of an ongoing, observational study. Relevant demographics, clinical data (e.g., SPSD phenotypes, comorbid conditions, and dates of diagnoses), and laboratory values were collected from electronic medical records. Lab values were excluded if completed within 6 months of receiving intravenous immunoglobin treatment. Summary statistics were performed and assessment for any associations between autoimmune comorbidities and disease burden (modified Rankin score [mRS] and ambulation status) was performed. Results: The majority of participants had classic SPS (66%), followed by SPS-plus (18%) and PERM (6%) with less than 5% each of the remaining phenotypes and suspected SPS. The average age at symptom onset in this cohort was 44.1 ± 14.5 years (mean ± standard deviation). The majority of the cohort was white (66%) and female patients (75%). The mean mRS was 2.5, and over 70% required assistive devices for ambulation. The most commonly identified non-neurological autoantibodies were anti-nuclear (ANA) (31%), thyroperoxidase (30%), thyroglobulin (20%), and anti-parietal cell (18%) autoantibodies. The most common comorbid autoimmune conditions were autoimmune thyroiditis (38%), insulin-dependent diabetes mellitus (26%), and pernicious anemia (10%). Having more autoimmune comorbidities was weakly associated with higher mRS and a greater need for ambulatory assistance. Conclusion: The results of this study will hopefully help promote awareness of which autoantibody and medical comorbidity clinicians should be aware of and monitor people with SPSD. Further research is needed to identify if poorly controlled non-neurological autoimmune disorders contribute to disease burden in SPSD and/or if the timing of being diagnosed with one of these conditions plays a role in future disability.