Background and Purpose: Steroid-responsive encephalopathy associated with autoimmune thyroiditis (SREAT) is a rare condition defined by encephalopathy with acute or subacute onset, the presence of serum anti-thyroid antibodies, and reasonable exclusion of alternative causes. Despite having strong response towards corticosteroid treatment, some patients exhibit a chronic-relapsing course and require long-term immunosuppression. Markers for early identification of those patients are still absent. Thus, we aimed to characterise clinical as well as laboratory parameters of our local SREAT cohort., Methods: We retrospectively evaluated a cohort of 22 SREAT patients treated in our hospital from January 2014., Results: A total of 14 patients with a monophasic disease course and eight patients with multiple relapses were identified. Neither baseline characteristics nor routine cerebrospinal fluid (CSF) parameters were able to distinguish between those patient groups. Flow cytometry following initial relapse therapy showed treatment-resistant sequestration of activated CD4+ T cells in patients with a relapsing disease course, whereas other lymphocyte subsets showed uniform changes. Such changes were also present in long-term follow-up CSF examination., Conclusion: Our findings indicate a potential biomarker for risk stratification in patients with SREAT. Currently, it remains unclear whether the observed two phenotypes are different spectra of SREAT or represent separate diseases in terms of pathophysiology., (© 2020 The Authors. European Journal of Neurology published by John Wiley & Sons Ltd on behalf of European Academy of Neurology.)