Natalizumab is used as an immunomodulatory treatment in relapsing-remitting multiple sclerosis (RRMS). Blood eosinophilia as an adverse effect has been described.
We aim to describe the frequency of blood eosinophilia and associated clinical symptoms in our monocentric cohort of natalizumab treated patients with relapsing remitting Multiple Sclerosis.
In our tertiary neurological care centre in Switzerland, we retrospectively longitudinally identified 115 natalizumab-treated and 116 untreated RRMS patients with eosinophil counts since July 2016 with our pharmacovigilance system and compared eosinophil counts, clinical symptoms and patient demographics.
In total, 44/115 natalizumab-treated patients (38%) developed eosinophilia (>0.4 G/l), which occurred significantly more frequently compared to 116 untreated MS patients (n=3; 3%). Of 44 natalizumab-treated patients with eosinophilia, 43 remained asymptomatic; one patient one patient developed an eosinophilic pneumonia after 2 infusions of natalizumab, which resolved without sequelae after cessation. All untreated MS patients with eosinophilia remained asymptomatic.
Our cohort confirmed that eosinophilia is a potential side effect of natalizumab in RRMS patients and most commonly remains asymptomatic. However, in one of our natalizumab-treated patients (0.9% of all patients), an eosinophilic pneumonia occurred as a rare but severe side effect. Physicians should be vigilant for symptoms of an eosinophilic disease in natalizumab-treated patients. Further studies on drug safety in real-life settings using automated big data approaches are warranted to better describe drug-associated adverse effects.