Systemic Lymphoma Masquerading as Multiple Sclerosis Relapse.

Multiple sclerosis (MS) is a chronic immune-mediated central nervous system disease that can affect both the brain and spinal cord. Given that MS can occur at any location in the brain or spinal cord and can lead to a variety of symptoms, this can lead to difficulty in diagnosing MS versus other conditions mimicking MS. Here we present a case of a 69-year-old female with a history of relapsing-remitting MS diagnosed in 2002 and melanoma status post-excision who exhibited progressive neurological decline over eight weeks characterized by right internuclear ophthalmoplegia, bilateral ataxia, and left hemiparesis sparing the face. Mimics of MS can include various inflammatory, neoplastic, infectious, metabolic, and genetic disorders. The diagnosis of MS-mimicking diseases can be especially challenging for someone with a known history of MS. A biopsy should be considered for new lesions seen on imaging if acute immunotherapies have no response to the clinical patient's symptoms. Given the wide variety of symptoms that can present with MS, it is important to keep a broad range of differential diagnoses when considering MS, even in those with a known history of MS.