Recurrent optic neuritis as the first presentation of monoclonal gammopathy of undetermined significance: a case report

BACKGROUND: Monoclonal gammopathy of undetermined significance (MGUS), which can be asymptomatic, is a premalignant proliferative disorder of plasma cells. The peripheral nervous system may be involved in MGUS, causing a monoclonal gammopathy associated peripheral neuropathy. However, involvement of the central nervous system (CNS) in MGUS was rarely reported. CASE PRESENTATION: Here we report a rare case of recurrent optic neuritis, as the first clinical presentation of MGUS, in an otherwise healthy 54-year-old Iranian male patient. He was treated with intravenous high-dose methylprednisolone for acute attacks and rituximab as maintenance therapy. The patient's vision recovered, and he did not experience any other attack in 2 years of follow-up. CONCLUSION: This case demonstrates that MGUS should be considered in the differential diagnosis of recurrent optic neuritis, expanding the spectrum of CNS involvement associated with this condition. The favorable response to immunotherapy suggests a possible immune-mediated mechanism.