Abstract
We report a rare case of recrudescence of natalizumab-induced pneumonitis and peripheral hypereosinophilia, hence uniquely satisfying the re-exposure principle outlined by the Naranjo Adverse Drug Reaction Probability Scale. A 57-year-old female with relapsing-remitting multiple sclerosis presented with acute respiratory symptoms, eosinophilia of 2.08 × 10(9)/L, and chest computed tomography showing consolidation of the right upper and lower lobes. Her septic and autoimmune work-up was negative. She did not improve with broad-spectrum antibiotics. Bronchoalveolar lavage revealed 75% lymphocytes. Upon discussion at a multi-disciplinary meeting, her antibiotics were discontinued and she was commenced on prednisolone, which resulted in immediate improvement. She experienced two further recurrences of pneumonitis during her prednisolone tapering. After a two-year remission, she was re-started on natalizumab due to adverse events related to alternative biologic agents. Her pneumonitis and peripheral hypereosinophilia recurred. She responded well to another course of prednisolone, and subsequent follow-up revealed complete recovery off natalizumab.