False positivity of anti aquaporin-4 antibodies in natalizumab-treated patients

Background: Neuromyelitis optica spectrum disorders (NMOSD) represent a differential diagnosis of multiple sclerosis (MS). Detection of anti-aquaporin-4 antibodies (AQP4-Ab) is the strongest argument to confirm NMOSD. Diagnosing NMOSD is a major concern because specific MS disease modifying drugs can lead to neurological worsening. Objective: To report the case of two natalizumab (NTZ) treated patients who presented a false positive result for AQP4-Ab. Methods: A retrospective analysis of NTZ-treated patients who were tested positive for AQP4-Ab in our MS center. Results: Two patients treated by NTZ presented a false positive result. Conclusions: Clinicians should be aware of potential technical issues in detecting AQP4-Ab in NTZ-treated patients leading to false positive results.