We report the case of a woman with multiple sclerosis who developed a severe neurological condition following natalizumab (NZB) withdrawal and soon after fingolimod (FTY) initiation. FTY was started 3.5 months after a two-year NZB treatment. Fifteen days later, she suffered partial repetitive seizures followed by a tonicoclonic seizure. This was associated with attention difficulties and an increased asthenia. Brain MRI follow-up disclosed large demyelinating active lesions in favour of disease reactivation. This case suggests that FTY introduction may occur less than three months after NZB withdrawal.
