Clinical Reasoning: A 30-Year-Old Female Patient With Multiple Sclerosis Presenting With Rapidly Progressive Cranial Neuropathies, Weakness, and Ataxia.

A 30-year-old woman with relapsing-remitting multiple sclerosis on ocrelizumab presented with subacute diplopia, dysarthria, spastic upper extremity diplegia, nausea, and vomiting. She was 4 months postpartum at the time of presentation and had resumed ocrelizumab infusions within 1 month after delivery. MRI demonstrated T2 hyperintensities involving the bilateral anterior medulla, substantia nigra, superior dorsal aspect of the pons, and right midbrain, with nonenhancing demyelinating lesions in the cervical and thoracic spinal cord. Extensive diagnostic testing was conducted, including evaluation of infectious, autoimmune, and paraneoplastic encephalitis causes. This case presentation discusses the causes and management of infectious rhombencephalitis, particularly in the setting of immunomodulatory therapy, and the nuance of infectious disease test result interpretation.