Probable flu vaccine- induced NMOSD relapse; This literature case from was received on 14-Mar-2023, reported by other healthcare professional and concerned an adult patient in late 30s, of an unreported gender.  This study objective was to evaluate the prevalence and clinical characteristics of iatrogenic central nervous system (CNS) inflammation in a tertiary neuroimmunology clinic since various vaccines, tumor-necrosis-factor-alpha inhibitors (TNFAIs), immune-checkpoint inhibitors (ICIs), and other immunomodulators had been linked to inflammatory CNS events. However, the prevalence of iatrogenic events in the neuroimmunology clinic is unknown.  The patient's concurrent conditions included systemic lupus erythematosus (SLE) and leukaemia. The patient's concomitant medications were not reported.  On an unspecified date, the patient was vaccinated with influenza vaccine (brand not specified; dose, route of administration, anatomical location and indication: not reported). The batch number was not reported.  On an unspecified date, 14 days after receiving influenza vaccine, the patient experienced spinal motor attack, possible flu vaccine induced neuromyelitis optica spectrum disorder (NMOSD) relapse. The diagnosis of NMOSD was established with anti-aquaporin-4 immunoglobulin G (AQP4- IgG). The patient was treated with methylprednisolone, reported as 'IVMP'.  At the time of initial reporting, the patient was recovering from the event. As reported, the patient had full response to corticosteroid therapy.  The reporter assessed the event to be probably related to influenza vaccine. As reported, the patient had probable flu vaccine induced NMOSD relapse.  The event of 'neuromyelitis optica spectrum disorder' was considered to be medically significant by a Physician within Seqirus's Pharmacovigilance and Risk Management Department.    This case is linked with cases 202301976, 202301977 and 202301986 (the same literature article).  Company comment: This study objective was to evaluate the prevalence and clinical characteristics of iatrogenic central nervous system (CNS) inflammation in a tertiary neuroimmunology clinic since various vaccines, tumor-necrosis-factor-alpha inhibitors (TNFAIs), immune-checkpoint inhibitors (ICIs), and other immunomodulators had been linked to inflammatory CNS events. An adult patient in late 30s was vaccinated with influenza vaccine. On an unspecified date, 14 days after receiving influenza vaccine, the patient experienced spinal motor attack, possible flu vaccine induced neuromyelitis optica spectrum disorder (NMOSD) relapse. The diagnosis of NMOSD was established with anti-aquaporin-4 immunoglobulin G (AQP4- IgG). The patient was treated with intravenous methylprednisolone, reported as 'IVMP'. Causal role of the vaccine is assessed as possibly related, due to plausible temporal relationship with the vaccine.; Reporter's Comments: As reported, the patient had probable flu vaccine induced NMOSD relapse.; Sender's Comments: This study objective was to evaluate the prevalence and clinical characteristics of iatrogenic central nervous system (CNS) inflammation in a tertiary neuroimmunology clinic since various vaccines, tumor-necrosis-factor-alpha inhibitors (TNFAIs), immune-checkpoint inhibitors (ICIs), and other immunomodulators had been linked to inflammatory CNS events. An adult patient in late 30s was vaccinated with influenza vaccine. On an unspecified date, 14 days after receiving influenza vaccine, the patient experienced spinal motor attack, possible flu vaccine induced neuromyelitis optica spectrum disorder (NMOSD) relapse. The diagnosis of NMOSD was established with anti-aquaporin-4 immunoglobulin G (AQP4- IgG). The patient was treated with intravenous methylprednisolone, reported as 'IVMP'. Causal role of the vaccine is assessed as possibly related, due to plausible temporal relationship with the vaccine.