Diagnosing Susac Syndrome Despite Incomplete Clinical Triad: A Case Report of Convergent Atypical Neuroimaging and Inflammatory Cerebrospinal Fluid Findings: Case Report

Background Susac syndrome (SuS) is a rare autoimmune endotheliopathy involving the brain, retina, and inner ear. Because patients frequently present without the complete clinical triad of encephalopathy, branch retinal artery occlusions (BRAO), and sensorineural hearing loss (SNHL), diagnosis can be challenging. The European Susac Consortium (EuSaC) criteria classify SuS according to objective involvement of the brain, retinal, and vestibulocochlear domains; however, many patients do not fulfill criteria for probable or definite disease at initial presentation. Furthermore, neuroimaging and cerebrospinal fluid (CSF) findings may overlap with inflammatory demyelinating disorders such as multiple sclerosis (MS). We report a case where EuSaC criteria was not met, however there was strong clinical and radiographic evidence to support the diagnosis of SuS. This case brings to question whether strict fulfillment of EuSaC criteria is needed to initiate early inpatient treatment to prevent irreversible neurological deficits. Case presentation We report the case of a woman in her early forties with hypertension, hyperlipidemia, chronic kidney disease, recurrent ischemic strokes, and an unspecified hypercoagulable disorder who presented with progressive gait instability, dizziness, and bilateral lower extremity weakness. Brain magnetic resonance imaging (MRI) demonstrated characteristic central corpus callosum “snowball” lesions and cerebellar leptomeningeal enhancement. CSF analysis revealed elevated immunoglobulin G (IgG) index, elevated IgG synthesis rate, and markedly elevated myelin basic protein (MBP) in the absence of oligoclonal bands (OCB). At the time of presentation, only the brain domain of the EuSaC criteria was objectively fulfilled, and the patient therefore did not meet criteria for probable or definite SuS. Nevertheless, the characteristic neuroimaging phenotype, inflammatory CSF profile without oligoclonal bands, and absence of typical MS features strongly favored SuS and prompted treatment with high dose steroids and further diagnostic evaluation. Conclusions This case demonstrates that strict fulfillment of EuSaC criteria may not be required to recognize SuS when characteristic neuroradiographic findings and supportive clinical features are present. Recognition of central corpus callosum “snowball” lesions and cerebellar leptomeningeal enhancement may facilitate earlier diagnosis and treatment, potentially reducing irreversible neurologic, retinal, and auditory morbidity.