Severe haematological complications during treatment with natalizumab.

The safety profile of natalizumab has been widely discussed due to several cases of progressive multifocal leukoencephalopathy, reported worldwide. Since the launch of natalizumab, 32 patients have been treated at our centre. In this context, we describe two cases (6.25%), one of immune-mediated acute haemolytic anaemia (IAHA) and another of immune thrombocytopenic purpura during treatment with natalizumab. The temporal relationship between drug administration and the nature of the haematological complications, confirmed with the serological findings in the case of the IAHA, suggests that natalizumab is the most probable cause for these adverse events. Although very uncommon, the haematological complications are severe enough to justify a close and careful monitoring for all patients with multiple sclerosis treated with an immunosuppressant treatment.