To investigate the presence of autoantibodies and their correlation to associated diseases in patients with anti-glutamic acid decarboxylase (antiGAD65-ab)-related Stiff Person Syndrome (SPS).

SPS is a rare disorder that can present with a variety of comorbid autoimmune conditions, the most recognized being type 1 diabetes mellitus and thyroiditis. Due to its rarity, there is lack of knowledge regarding the presence of coexisting autoantibodies and their related comorbid conditions in SPS.

One-hundred and twenty-five antiGAD65-ab positive SPS patients were identified through retrospective review of medical records at Johns Hopkins Hospital from 1997 to 2018. Systemic autoantibodies included anti-thyroid, -gastric parietal cell, -nuclear antibodies, -dsDNA, -Ro, -La, amongst others. Patients without serum testing for systemic autoantibodies were excluded. Also, patients who received IVIG within 12 months of testing for serum autoantibodies were excluded.

Thirty-nine patients were eligible for this study. Average age of the cohort was 54 years and majority were female (29). Mean serum anti-GAD65 level was 56,647 IU/mL. Thirty-five patients had at least one elevated systemic autoantibody. Most commonly elevated autoantibodies were gastric parietal cell (12 of 19 patients that were tested), anti-nuclear (15 of 38: titer range; 1:80 to ≥1:640), Thyroperoxidase (12 of 25), and Thyroglobulin (9 of 35) antibodies. The most commonly comorbid autoimmune conditions were: Autoimmune thyroiditis (n=9), Type 1 Diabetes (n=5), Pernicious anemia (n=4), and Sjogren’s syndrome (n=3). One patient had systemic lupus erythematosus.

This study characterizes the presence of pertinent systemic autoantibodies and related comorbid conditions in a large cohort of individuals with SPS. These findings further support the need to assess for co-existing autoimmune conditions in SPS and helps promote awareness on what autoantibodies may be relevant to check in this patient population.