Tumefactive multiple sclerosis; Dizziness; slurred speech; impaired coordination; changes in mental status; abulia; generalized weakness; dysmetria; shuffling gait; weakness more prominent in the right extremities; space-occupying lesions/lesions in the bilateral cerebral and left cerebellar hemispheres; The lesions showed mild surrounding edema; being able to get out of bed; being able to feed herself; This case was reported in a literature article and described the occurrence of tumefactive multiple sclerosis in a 29-year-old female patient who received HBV (Engerix B) for prophylaxis.    The patient's past medical history included hepatitis c. Previously administered products included Influenza vaccine with an associated reaction of no adverse event (had multiple shots of the influenza vaccine in the past without any complications). Concurrent medical conditions included bipolar disorder (not on medication) and substance use disorder (with a recent injection of suboxone pills). Concomitant products included INFLUENZA VACCINE and buprenorphine hydrochloride + naloxone hydrochloride (Suboxone).   On an unknown date, the patient received Engerix B. On an unknown date, 1 day after receiving Engerix B and an unknown time after receiving INFLUENZA VACCINE, the patient experienced tumefactive multiple sclerosis (serious criteria hospitalization, GSK medically significant and clinically significant/intervention required), dizziness (serious criteria hospitalization), slurred speech (serious criteria hospitalization), coordination impaired (serious criteria hospitalization), mental status changes (serious criteria hospitalization), abulia (serious criteria hospitalization), weakness generalized (serious criteria hospitalization), dysmetria (serious criteria hospitalization and GSK medically significant), gait shuffling (serious criteria hospitalization), weakness in extremity (serious criteria hospitalization), brain lesion (serious criteria hospitalization and clinically significant/intervention required), brain edema (serious criteria hospitalization, GSK medically significant and clinically significant/intervention required), bedridden (serious criteria hospitalization) and activities of daily living impaired (serious criteria hospitalization). The patient was treated with dexamethasone, vancomycin, meropenem, methylprednisolone, prednisone and operations and procedures (Plasmapheresis (Nos)). On an unknown date, the outcome of the tumefactive multiple sclerosis, dizziness, slurred speech, coordination impaired, mental status changes, abulia, weakness generalized, dysmetria, gait shuffling, weakness in extremity and brain edema were recovering/resolving and the outcome of the brain lesion, bedridden and activities of daily living impaired were recovered/resolved.   The reporter considered the tumefactive multiple sclerosis, dizziness, slurred speech, coordination impaired, mental status changes, abulia, weakness generalized, dysmetria, gait shuffling, weakness in extremity, brain lesion, brain edema, bedridden and activities of daily living impaired to be related to Engerix B.     Additional Information: GSK Receipt Date: 11-Nov-2022 Author's comment:  The patient's medical history was significant for bipolar disorder not on medication, hepatitis C, and substance use disorder with a recent injection of suboxone pills. The patient presented to the emergency department with dizziness, slurred speech, and impaired coordination for six days. The patient reported that her symptoms began one day after receiving the hepatitis B and flu vaccine. Her condition gradually worsened with changes in mental status, abulia and generalized weakness. On examination, the patient was afebrile with a heart rate of 55 beats/minute, blood pressure of 122/72 mmHg, respiratory rate of 13 breaths/minute and oxygen saturation of 100%. Cardiovascular, respiratory, and abdominal examinations were unremarkable. Neurologic examination was pertinent for slurred speech, dysmetria, shuffling gait, and weakness more prominent in the right extremities. On further neurologic examination, the patient had intact gross sensations and cranial nerve functions, deep tendon reflexes were normal, her neck was supple, and no signs of meningeal irritation were noted. Lab results on admission were unremarkable. A computed tomography (CT) scan of the head without contrast revealed multifocal underlying space-occupying lesions. Magnetic resonance imaging (MRI) of the brain with and without contrast revealed multiple rim-enhancing lesions of varying sizes in the bilateral cerebral and left cerebellar hemispheres. The lesions showed mild surrounding edema. Transverse sections of T2-weighted brain magnetic resonance imaging showing enhancing lesions in the right cerebral, left cerebellar, and left cerebral hemispheres. Other imaging modalities were unremarkable, including CT scans of the chest, abdomen, pelvis, and transthoracic and transesophageal echo. The infectious workup was normal, including blood cultures, human immunodeficiency virus, syphilis serology, toxoplasma serology, and Lyme serology. Hepatitis C RNA was undetectable. Because of the imaging results and recent intravenous drug use, the patient was started on dexamethasone, vancomycin, and meropenem for 12 days. Following no improvement, the patient underwent a stereotactic burr hole biopsy/drainage of left frontal and left cerebellar lesions. The frozen section was significant for hypercellular glial tissue, and cultures showed no growth. Tissue histology revealed macrophages and lymphocyte infiltrates, with myelin loss and gliosis suggestive of a malignant/tumefactive form of Multiple Sclerosis (MS). The patient was switched to methylprednisolone for seven days and then tapered on oral prednisone. Subsequently, the patient was treated with plasmapheresis; with the plasmapheresis, the patient saw an immediate improvement in her symptoms including being able to get out of bed and being able to feed herself. The patient received a total of six rounds of plasmapheresis. However, over the course of two years, the patient did not develop any further neurological attacks, and her repeat brain MRI one year and two years later did not show any new interval lesion development. The patient needs to be continually monitored for any further neurological symptoms and new lesions on brain MRI for a confirmed diagnosis of MS. However, on initial presentation, it seemed like the patient had tumefactive MS.  "This patient developed neurological symptoms one day after receiving the hepatitis B and influenza vaccine. She has had multiple shots of the influenza vaccine in the past without any complications, but this was her first exposure to the hepatitis B vaccine. The safety and efficacy of vaccines are well documented in the literature. Still, there is an established association between vaccines and neurologic demyelinating syndromes, particularly Guillain-Barré syndrome with the influenza vaccine and MS with the yellow fever vaccine The hepatitis B vaccine received scrutiny due to a surge in MS cases following mass immunization in France. Since then, several studies have been conducted to assess possible correlations. It is also interesting to note that the patient in this case report received the ENGERIX-B/RECOMBIVAX HB hepatitis B vaccine, and one case-control study involving children based in France reported that although the hepatitis B vaccine did not increase the risk of MS in general, "the Engerix B vaccine appeared to increase the risk, specifically for confirmed MS, in the longer term." The study mentioned that their results required confirmation in future studies. "The immune response in MS can be triggered by various environmental factors, one of which may be vaccines. It is critical for healthcare providers to be aware of the different side effects of vaccines and consider vaccines as the potential cause of the abnormality. In this case, the temporal relationship between receiving the hepatitis B vaccine, and the onset of symptoms makes us wonder whether there could be a causal relationship between the two. However, further studies are needed to assess the association between the hepatitis B vaccine and MS. Meanwhile, we would like to emphasize that clinicians should also suspect MS in patients presenting with neurologic symptoms days to weeks following hepatitis B vaccination." Additional supportive information: The article corresponding to this case is not available for regulatory submission due to copyright restriction.