Severe Disease Activation after Fingolimod Discontinuation in a Pediatric Multiple Sclerosis Patient: A Case Report and Literature Review.

Adult reports of unexpected severe disease worsening, often termed "rebound," shortly after discontinuing fingolimod in a subset of patients with multiple sclerosis (MS), have grown over the last decade. This phenomenon, however, remains poorly described in pediatric MS patients. We present findings of a 15-year-old who experienced a debilitating relapse 4 weeks after stopping fingolimod to switch to ocrelizumab. Imaging revealed multiple large new lesions far exceeding any previously observed activity level in the patient. Despite prompt high-dose corticosteroids, plasma exchange, and prolonged rehabilitation therapy, significant residual deficits involving cognition, balance, and vision remain from the attack. This case underscores that pediatric MS patients are also at risk of severe disease deterioration after fingolimod withdrawal and require close monitoring when switching therapies.