Elsberg syndrome following acute immunosuppressive treatment for multiple sclerosis relapse.

First described more than 80 years ago, Elsberg Syndrome (ES) continues to be an under-recognized cause of cauda equina syndrome (CES). ES is an infectious disorder that presents with lower thoracic and/or lumbosacral myelitis in conjunction with CES, and most often occurs in the setting of herpes simplex virus 2 (HSV-2) reactivation (Savoldi et al., 2017; Eberhardt et al., 2004; Whalen et al., 2019). Comorbid neurologic diseases like multiple sclerosis (MS) can become a detrimental confounding factor leading to delayed diagnosis and management of ES due to pre-existing diagnostic bias. We present a case of relapsing-remitting MS (RRMS) complicated by ES, likely due to reactivation of a latent HSV infection following high immunosuppression for presumed refractory MS relapses.