Neuromyelitis optica spectrum disorder; Condition aggravated; numbness and paresthesia in the posterior neck and right upper back; paresthesia in the posterior neck and right upper back; right-sided weakness; decreased sensation in the right V3 distribution of the face; bicep weakness/right extensor hallucis longus weakness graded at 3/5; right foot drop; 3 plus asymmetric hyperreflexia in the right bicep and right patellar tendon; acute enhancing lesion extending from C1 to C4; This case was reported in a literature article and described the occurrence of neuromyelitis optica spectrum disorder in a 31-year-old female patient who received Flu Seasonal QIV Dresden (Influenza vaccine Quadrivalent unspecified season) for prophylaxis.   The patient's past medical history included multiple sclerosis, no light perception (in the left eye experienced in 2011), neurological disorder nos (in 2011), leukopenia and hypocomplementemia. Previously administered products included steroids (high dose), interferon- beta and Influenza vaccine (since 2015, received yearly vaccinations without issue). Concurrent medical conditions included neuromyelitis optica spectrum disorder (disease was in remission by 2011), systemic lupus erythematosus (diagnosed in 2017 and was in remission by 2018), alopecia and inflammatory arthritis. Concomitant products included hydroxychloroquine.   On an unknown date, the patient received Influenza vaccine Quadrivalent unspecified season. On an unknown date, 1 month after receiving Influenza vaccine Quadrivalent unspecified season, the patient experienced neuromyelitis optica spectrum disorder (serious criteria hospitalization and GSK medically significant), condition aggravated (serious criteria hospitalization), numbness (serious criteria hospitalization), paresthesia (serious criteria hospitalization), weakness left or right side (serious criteria hospitalization and GSK medically significant), sensory disturbance (serious criteria hospitalization), muscle weakness (serious criteria hospitalization), foot drop (serious criteria hospitalization), hyperreflexia (serious criteria hospitalization) and vertebral lesion (serious criteria hospitalization). The patient was treated with methylprednisolone and rituximab. On an unknown date, the outcome of the neuromyelitis optica spectrum disorder, condition aggravated, numbness, paresthesia, weakness left or right side, sensory disturbance, muscle weakness, foot drop, hyperreflexia and vertebral lesion were recovered/resolved.   It was unknown if the reporter considered the neuromyelitis optica spectrum disorder, condition aggravated, numbness, paresthesia, weakness left or right side, sensory disturbance, muscle weakness, foot drop, hyperreflexia and vertebral lesion to be related to Influenza vaccine Quadrivalent unspecified season.  Additional details were provided as follows: This case was reported in a literature article and described the occurrence of Neuromyelitis optica spectrum disorder (NMOSD) Flare, in a 31-year-old female patient, who was vaccinated with unspecified Influenza vaccine (manufacturer unknown) for prophylaxis.   The patient was a woman. In 1999, the patient was diagnosed with multiple sclerosis (MS) on the basis of central nervous system (CNS) imaging and cerebrospinal fluid studies. During a period of sixteen years, the patient was treated with high-dose steroids and interferon- beta. The patient's diagnosis was later revised to NMOSD when the patient tested positive for AQP4-IgG in 2007. The patient disease was in remission by 2011, with residual neurologic deficits of no light perception in the left eye. Magnetic resonance imaging (MRI) of the brain and total spine in 2015. In 2017, the patient was diagnosed with SLE on the basis of positive anti-nuclear, anti-double stranded deoxyribonucleic acid, anti-Smith, and anti-ribonucleoprotein antibodies, leukopenia, hypocomplementemia, alopecia, and inflammatory arthritis. The patient was started on hydroxychloroquine for improvement in inflammatory arthritis, white blood cell counts, and complement levels. In 2018, the MRI the brain and total spine showed stable C6 hyperintense lesion extending to T8 myelomalacia with no active inflammation, which was unchanged from a prior spine MRI of the patient. SLE was in remission by 2018. No information on patient family history was reported.  Since 2015, the patient had received yearly influenza vaccinations without issue. In 2019, the patient was vaccinated with unspecified Influenza vaccine (administration route and site unspecified, dosage unknown; batch number not provided).   On an unspecified date in 2019, hours after vaccination, the patient developed numbness and paresthesia in the posterior neck and right upper back. Paresthesia worsened over the following three weeks with spread to the right arm, right hand, and right leg. The patient with NMOSD and SLE in remission presented with progressive paresthesia and right-sided weakness one month after receiving an influenza vaccination. By the time the patient was evaluated in rheumatology clinic (four weeks after vaccination), her sensory symptoms had spread to include her left leg. Physical exam was notable for decreased sensation in the right V3 distribution of the face, right bicep weakness graded at 4/5, right extensor hallucis longus weakness graded at 3/5, and right foot drop. The patient also had 3 plus asymmetric hyperreflexia in the right bicep and right patellar tendon. The patient was referred to the emergency room for further evaluation. Upon arrival, MRI with contrast of the brain, cervical, and thoracic spine revealed an acute enhancing lesion extending from C1 to C4. There was a new C2-C4 longitudinal lesion noted on the C spine on T2WI with associated patchy postcontrast enhancement on T1WI an ongoing hyperintense lesion in the T spine extending to T8. The patient was admitted for management of an NMOSD relapse. The patient received methylprednisolone 1000 mg intravenous (IV) daily for a total of five doses, plasmapheresis daily for 5 exchanges, and one dose of rituximab 1000 mg IV following plasmapheresis with complete return of neurologic exam to baseline. The patient had no serologic or clinical evidence of a contemporaneous SLE flare, and thus, a single dose of rituximab for NMOSD treatment, as opposed to the 2 doses commonly used in SLE treatment, was administered. Hydroxychloroquine was continued without changes. Rituximab 1000 mg IV every 6 months was continued as maintenance therapy for NMOSD. The case was considered as serious due to hospitalization. Treatment was unknown. Outcome was not reported. The authors commented "Here, we present three cases of SLE and NMOSD that highlights the importance of timely diagnosis of these coexistent conditions in order to guide therapeutic management. In NMOSD, recent data suggest that rituximab, eculizumab, satralizumab, and inebilizumab are most effective in preventing relapse although these therapies have been mainly studied in AQP4-IgG seropositive patients. We describe a 31-year-old woman who suffered an NMOSD flare after 11 years of clinical remission in the context of receiving an influenza vaccination; her SLE remained quiescent on hydroxychloroquine.". The authors concluded "We describe three cases of coexistent SLE and NMOSD, with several differences in clinical presentation. In the first case, the patient experienced an NMOSD flare in the setting of quiescent SLE and a known NMOSD diagnosis. In the second case, the patient had an initial NMOSD flare in the setting of active SLE. In the third case, the patient had an initial NMOSD flare in the setting of well-controlled SLE. These cases illustrate that SLE and NMOSD may coexist, and this may not be uncommon. The clinical manifestations of myelitis are similar in both SLE and NMOSD, and MRI findings of longitudinal cord swelling and hyperintensity in central cord regions may be seen with both disorders. It is critical to determine which disease is clinically active in order to appropriately tailor therapy. Though both disorders share similar neurologic manifestations, antibody testing for AQP4-IgG and MOG-IgG may help identify coexisting NMOSD. Based on our experience caring for these three patients and studies to date, we recommend that clinicians consider testing for AQP4-IgG and MOG-IgG in SLE patients with neurologic signs and symptoms. In seronegative cases where NMOSD is suspected but not supported by antibody testing, we recommend that these patients still be treated for NMOSD if imaging and CSF findings meet diagnostic criteria for this entity. It is imperative to identify coexisting SLE and NMOSD as treatment differs, and inappropriate treatment can lead to irreversible and severe neurologic outcomes".