Introduction: Pediatric-Onset Multiple Sclerosis (POMS) is characterized by high inflammatory disease activ-ity. Our aim was to describe the treatment sequencing and report the impact Highly Effective Disease Modifying Treatment (HET) had on disease activity. Materials and Methods: 2/5 consecutive POMS were administered HET as initial therapy after diagnosis. Data on treatment sequencing, relapses and MRIs were collected during the follow-up. Results: Our patients had an average age of 13.8 years (range 9-17) at di-agnosis and 13.4 years (range 9-16) at disease onset, 2/5 (40%) POMS were female. The pre-treatment aver-age annualized relapse rate was 1.6 (range 0.8-2.8) and the average follow-up length was 5 years (range 3-7). A total of 2/5 (40%) patients were stable on HET at initial therapy, 3/5 (60%) required an escalation to more aggressive treatment, even if two of them had been put on HET as initial treatment. Four out of five patients (80%) had No Evidence of Disease Activity-3 status (NEDA-3) at an average follow-up of 3 years (range 2-5). Conclusion: it has been observed that in a recent time period all the cases had prompt diagnosis, early HET or escalation to HET with a good outcome in 80% of the cases.

A 68-year-old man with malignant metastatic melanoma in complete remission after Pembrolizumab treatment, developed 10 months after Pembrolizumab cessation due a grade 3 diarrhea, confusion, altered mental status, progressive memory loss, gait disturbance. He was admitted to the neurologic department and comprehensive neurological workup, brain magnetic resonance imaging, cerebral fluid analysis, EEG, blood test allowed the diagnosis of autoimmune encephalitis. The patient was treated with plasmapheresis, high dose of intravenous steroids and intravenous immunoglobulins. The patient improved and he is now well with a performance status 1. This case is interesting since the AE developed approximately 10 months after the cessation of immunotherapy, the underlying cancer was in complete remission and the AE showed a good response to the treatment done.