Clinical Characterization and Prognostic Risk Factors of Susac Syndrome: A Retrospective Multicenter Study

Abstract

Background and objectives: Susac syndrome (SuS) is a rare disorder characterized by encephalopathy, branch retinal artery occlusion, and sensorineural hearing loss, often accompanied by vertigo. Recent updates to diagnostic criteria and treatment guidelines have been made. This study examines clinical manifestations; disease activity; and risk factors of disability, dependency, and return to work in patients with SuS.

Methods: A retrospective multicenter study was conducted on 20 consecutive patients with SuS with at least 2 years of follow-up. Clinical and paraclinical activities were assessed and rated according to the severity at onset and the end of follow-up. Cognitive function was assessed using the Montreal Cognitive Assessment while disability and dependence in daily activities were measured using the modified Rankin Scale. Employment status was graded.

Results: The mean age at onset was 38.9 years, with a mean follow-up of 55.9 months. The female-to-male ratio was 1.86, and 45% of patients had the complete clinical triad. Severe cerebral involvement at onset was associated with a higher risk of cerebral exacerbations within the first year and with an increased long-term disability and dependency. Cognitive function improved in 75% of patients during follow-up. At disease onset, hearing loss excluding low frequencies occurred in 46.7%. Relapse of hearing loss was associated with greater impairment in daily activities. Male sex and elevated CSF protein levels were linked to poorer prognosis. Cerebral and inner ear exacerbations were most common in the first year while retinal exacerbations occurred more frequently, mainly within the first 2 years. Approximately 50% of patients resumed employment while 25% did not return to work.

Discussion: Current treatment strategies for SuS do not fully prevent relapses. Severe brain manifestation at onset, male sex, and high CSF protein levels are risk factors of a worse prognosis of disability and dependence, indicating the need for intensive treatment. High-frequency hearing loss does not exclude SuS diagnosis.

Figure 1. Change in the MoCA Test Score During the Follow-Up Period

Twelve patients with cerebral involvement at SuS onset were assessed with MoCA at disease onset and follow-up, showing a significant improvement in scores over time. MoCA = Montreal Cognitive Assessment.

Figure 2. Correlation Between Cerebral Manifestation Severity at SuS Onset and Disability and Dependency Prognosis

A significant positive correlation was found between the severity of cerebral manifestations at SuS onset and disability and dependency at follow-up, as measured using the modified Rankin Scale. SuS = Susac syndrome.

Figure 3. Correlation Between CSF Total Protein Concentration and Disability and Dependency Prognosis

A significant positive correlation was found between CSF total protein levels at diagnosis and disability and dependency at the end of the follow-up, as measured using the modified Rankin Scale.