1422 High-Dose Rivastigmine in REM Behavior Disorder - A Therapeutic Coincidence or Stroke of Luck?

Abstract Introduction Stiff Person Syndrome (SPS) is an autoimmune neurological disorder associated with anti-GAD65 antibodies where stiffness and spasms of axial and limb muscles are the common manifestations. Other atypical features now being recognized are cranial neuropathies, sensory ataxia, and REM sleep behavior disorder (RBD). Report of case A 62-year-old woman with seronegative rheumatoid arthritis and positive GAD65 antibody presented with gait instability in 2015 and was given the diagnosis of SPS. Her diseased progressed to include cranial neuropathies (dysarthria, dysphagia, diplopia), sensory ataxia, torso stiffness, autonomic instability (syncope, nausea, sweating), and REM sleep behavior disorder. Immunosuppressive treatments rituximab, methotrexate and hydroxychloroquine showed some improvement in symptoms. Rituximab was stopped in 2020 because of the pandemic and regarding immune suppression. Her stiffness, and RBD worsened. In 2024 the patient received IVIG therapy every 3 weeks and noticed improvement in some symptoms but continued to have bothersome RBD. However, the RBD improved after being placed on rivastigmine. This case demonstrates how SPS with atypical multi-system symptoms can be difficult to manage. Cranial neuropathies, RBD, autonomic symptoms and sensory ataxia are not common but have been described more frequently in SPS and might be associated with neuroinflammation. IVIG was effective in reducing muscle spasticity and, improving the quality of sleep and minimizing the number of medications currently being administered. Its action might be explained by the regulation of neuroinflammation and the immune response. However, cranial neuropathies, autonomic symptoms and RBD remained challenging the patient, suggesting the non-reversible damage which is not uncommon with autonomic dysfunction. Conclusion This case shows the complexity of treating symptoms associated with SPS. Further studies are required to determine the treatment’s effectiveness overall and to define its role in the management of cranial and autonomic symptoms. Multiple disciplines must be involved in managing SPS patients with atypical features to ensure the best outcome. Support (if any)