Severe febrile neutropenia associated with satralizumab in an Argentinian neuromyelitis optica spectrum disorder patient

Background: Recently, satralizumab (interleukin-6 receptor blocker) was approved for seropositive neuromyelitis optica spectrum disorder (NMOSD) patients. In SAkuraSky trial, mild neutropenia was reported in 15% of patients under satralizumab. Most neutropenias were transient; grade 3-4 was not related to serious infections. So far, no severe neutropenia (<100 cell/mm(3)) has been reported worldwide. Methods: We present an aquaporin-4-antibody-positive NMOSD patient who developed severe febrile neutropenia 2 weeks after adding satralizumab to her azathioprine treatment. Conclusion: Analytic control for satralizumab is recommended at 4 weeks. However, we recommend this control at week 2, in order to closely monitor neutrophil count and prevent further complications.