High-Risk PML Patients Switching from Natalizumab to Alemtuzumab: an Observational Study.

INTRODUCTION: The choice of therapy in patients withdrawing from natalizumab treatment is still an open question and neurologists need strategies to manage this group of patients. The aim of this study is to evaluate if alemtuzumab is able to control the disease when used in patient who have stopped natalizumab.

METHODS: 16 patients stopped natalizumab treatment after a median number of 20 infusions (range 12-114); all the patients were responders to natalizumab (neither clinical nor radiological activity during natalizumab therapy) and the reason for stopping was the risk of PML for all of them. Patients were switched to alemtuzumab after a median wash-out period of 70 days (range 41-99 days); patients underwent brain MRI every three months during natalizumab treatment and then just before starting alemtuzumab in order to exclude signs suggestive of PML; then, contrast-enhanced brain MRI was planned 6 and 12 months after alemtuzumab infusion.

RESULTS: At present, 8 out of 16 patients have a follow-up >6 months and 2 out of 8 reached 1-year follow-up; 5 have a follow-up of 3-6 months and 3 have a follow-up <3 months. Brain MRI at 6 months after alemtuzumab is available for 8 out of 16 patients and in all of them, neither signs of disease activity nor new lesions are present; in 2 out of 8 patients, brain MRI at 12 months is also available, showing no sign of disease activity. Clinical evaluation performed at 6 and at 12 months (when available) showed stability, in particular neither relapses nor increase in EDSS were observed.

CONCLUSIONS: Alemtuzumab was able to control the disease course in patients who stopped natalizumab; of course, as this is a single-centre study and the number of patients is small, these findings are very preliminary and need further confirmation.