Extensive rebound MS activity following dimethyl fumarate discontinuation in a 63 year old – A case report

Background: Dimethyl fumarate (DMF) is an oral disease modifying therapy (DMT) approved for the treatment of relapsing-remitting multiple sclerosis (RRMS). DMF is effective at reducing relapses, and decreasing disease activity. Reports of rebound activity following DMF discontinuation are rare. Case report: We report the case of a 63-year old woman with RRMS, showing an extensive radiological and clinical rebound after DMF discontinuation. She started DMF in 2014 at which time her EDSS was 1.5. She was clinically stable until 2019, when she noted the onset of progressive left leg weakness but without signs of radiological activity on brain MRI. In 2020, she experienced further worsening and MRI showed one new brain lesion. She was treated with oral steroids with partial recovery. She self-discontinued DMF in February 2021. Approximately 5 months after discontinuation she developed severe left side weakness and her brain MRI showed 34 enhancing lesions. She was treated with another course of oral steroids with clinical benefit and her DMT was switched to oral cladibrine. Conclusions: This case is unusual because MS disease rebound is uncommon after DMF discontinuation and because disease activity of this magnitude with over 30 gadolinium enhancing lesions is rare in people with MS over the age of 60. Our case stresses that a reactivation of MS activity including a large number of enhancing lesions can occur in older individuals, despite a presumably senescent immune system. Monitoring for disease activity before and after discontinuing a DMT is important, regardless of the patient's age.