Immunosuppressive agents or intravenous immunoglobulin in addition to glucocorticoids in the treatment of Susac syndrome: a French national cohort study.

Background: Susac syndrome is a rare disease affecting mainly young women and is characterised by an occlusive microvessel disease limited to the brain, retina, and inner ear. No randomised controlled trial has been published or declared as ongoing to investigate treatments for Susac syndrome. We aimed to compare the effect of glucocorticoids given alone or in combination with immunosuppressive agents or intravenous immunoglobulin for the prevention of relapse in patients with Susac syndrome.

Methods: The Phenotypic and Etiological Characterization of Susac Syndrome-National Clinical Research Hospital Program study is a prospective national cohort study that started enrolling on Nov 29, 2011, and included all consecutive patients aged 18 years or older with Susac syndrome who were referred to the French reference centre (Department of Internal Medicine, Bichat-Claude Bernard Hospital, Paris). Susac syndrome was defined by either the triad of encephalopathy with typical brain MRI abnormalities, cochleo-vestibular damage, and multiple occlusions of retinal central artery branches, or at least two of the three criteria without any alternative diagnosis. Collected data included fundoscopy, retinal angiography, audiometry, cerebrospinal fluid, brain MRI, and treatment received at diagnosis; months 1, 3, 6, and 12 after diagnosis; and then annually for 5 years or in the case of a relapse. The primary outcome was defined as the first relapse occurring within a 36-month follow-up period from the first day of treatment, characterised by new clinical symptoms or signs, and new abnormalities observed on retinal angiography, audiometry, or brain MRI, necessitating treatment intensification. There was no involvement of people with lived experience at any stage. The study is registered at ClinicalTrials.gov, NCT01481662.

Findings: Between Nov 29, 2011, and Dec 2, 2022, 64 patients were included in the study, with a mean age at diagnosis of 35 years (SD 11); 41 (64%) were women and 23 (36%) were men. At diagnosis, 60 patients received glucocorticoids; 40 (63%) of 64 patients received glucocorticoids alone as a first-line therapy while 20 (31%) received glucocorticoids in combination with immunosuppressive agents or intravenous immunoglobulin. Overall, 46 (72%) of 64 patients had a first relapse with a median relapse-free survival time of 3·96 months (95% CI 2·24-16·07). Comparison of relapse-free survival showed no significant difference between the two treatment strategies (hazard ratio [HR] 1·11 [95% CI 0·56-2·17], p=0·76), compared with glucocorticoids alone as the reference group. In patients who first relapsed while treated with glucocorticoids alone, there was no significant difference in second relapse-free survival between those who did or did not receive immunosuppressive agents or intravenous immunoglobulin as a second-line therapy (HR 2·66 [95% CI 0·63-11·18], p=0·18).

Interpretation: The combination of glucocorticoids with immunosuppressive agents or intravenous immunoglobulin did not appear to reduce the risk of Susac syndrome relapse compared with glucocorticoids alone. Our findings did not support the systematic use of immunosuppressive agents in Susac syndrome.

Funding: French Ministry of Health.