JCN Open Access LETTER TO THE EDITOR pISSN 1738-6586 / eISSN 2005-5013 / J Clin Neurol 2021;17(4):573-575 / https://doi.org/10.3988/jcn.2021.17.4.573 Cerebral Venous Sinus Thrombosis After Pfizer-BioNTech COVID-19 (BNT162b2) Vaccination Newman Cheng Dear Editor, Department of Neurology, National Neuroscience Institute - Singapore General Hospital, Singapore While there have been reported cases of cerebral venous sinus thrombosis (CVST) related to the ChAdOx1 nCoV-19 and Ad26.COV2.S vaccines,1,2 we are not aware of any previous lo- cal report of a case of CVST that is temporally associated with the Pfizer-BioNTech COVID-19 (BNT162b2) vaccine in Singapore. With 35 possible comparative cases3 among 54 million re- cipients of the BNT162b2 vaccine reported to the European Medicines Agency, the present case had a similar clinical presentation with no other known risk factors for CVST, to which standard treatment4 of anticoagulation and seizure management was applied. A 61-year-old Chinese male with diabetes mellitus had received his first dose of the BNT162b2 vaccine on March 19, 2021. He reported soreness at the local injection site lasting for a few days, but did not experience fever, headache, or flu-like symptoms. He was asymptomatic before re- ceiving his second dose of the BNT162b2 vaccine on April 10, 2021. Five days thereafter he complained of worsening generalized headache associated with persistent vomiting over the following 2 days, leading to his hospital presentation. He did not notice any double vision, fa- cial droop, slurring of speech, focal limb weakness, or numbness, and there was no history of recent trauma, infection, dehydration, or constitutional symptoms. He was a nonsmoker and denied taking any other drugs apart from his diabetic medications. There was no family or personal history of prior venous thromboembolic disease. On clinical examination, he had a normal body mass index and was alert and rational. Cranial nerves, limb reflexes, and mo- tor and sensory testing were unremarkable. There was a left extensor Babinski response. A computed tomography (CT) scan of the brain on admission revealed acute subarachnoid hem- orrhage (SAH) along the left frontal lobe sulci (Fig. 1A). On the following day, the patient was witnessed to have a focal-onset motor seizure involv- ing left head version and left upper limb tonic-clonic jerking lasting for 5 minutes. Repeat brain CT revealed several new acute intraparenchymal hematomas in the right frontal lobe with overlying hyperdense cortical draining veins (Fig. 1B and C). Brain magnetic resonance imaging with venography subsequently showed thrombosis of the entire superior sagittal sinus extending to the medial portion of the right transverse sinus (Fig. 1D). Additional findings included bilateral frontal lobe cortical vein thrombosis, partial thrombosis of bilateral sigmoid sinuses, right frontal lobe intraparenchymal hemorrhage with edema that was consistent with a venous infarct, and bilateral frontal and parietal convexity SAH. The blood platelet count was normal at 333,000/μL, and there was no evidence of dissemi- nated intravascular coagulopathy. A further prothrombotic workup including lupus antico- agulant, anticardiolipins, homocysteine, protein C, protein S, antithrombin III, and thyroid func- tion produced unremarkable findings. CT of the thorax, abdomen, and pelvis did not reveal any malignancy or occult vessel thrombosis. An RT-PCR for SARS-CoV-2 was negative. The patient was commenced on low-molecular-weight heparin at 1 mg/kg bid and convert- cc This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Com- mercial License (https://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Copyright © 2021 Korean Neurological Association 573 Received May 14, 2021 Revised Accepted July 7, 2021 July 8, 2021 Correspondence Newman Cheng, MBBS (Singapore), MRCP (UK), MMed (IM), MRCP (Neurology) Department of Neurology, National Neuroscience Institute - Singapore General Hospital, 20 College Road, Singapore 169856 Tel +65-6326-4509 Fax +65-6326-5003 E-mail newman.cheng@gmail.com A B C Fig. 1. Neuroimaging showing intracerebral hemorrhages and cerebral venous sinus thrombosis. A: Axial and coronal brain CT on admission showing hyperdensities along the left frontal lobe sulci suggestive of SAH. B and C: Axial and coronal brain CT repeated 1 day later showing sever- al new acute intraparenchymal hematomas in the right frontal lobe with sizes up to 1.3 cm. There were also hyperdense cortical draining veins over the right frontal lobe (green arrows). The left frontal lobe sulci SAH was stable. D: Sagittal brain T1-weighted MRI (left image) showing T1- weighted hyperintensity over the entire SSS (blue arrow) extending to the right transverse sinus, compatible with thrombus. The MRI venogram (right image) reveals that flow was absent in the SSS (red arrow). SAH, subarachnoid hemorrhage; SSS, superior sagittal sinus. D ed to oral warfarin (international normalized ratio=2–3) since he remained neurologically stable. He was also started on le- vetiracetam at 500 mg bid with no recurrence of seizures. To date, more than 4 million doses of the BNT162b2 vaccine have been administered in Singapore. The present case report is the first of a local case of CVST that is temporally associated with the vaccine. There is still insufficient evidence that the rate of CVST associated with COVID-19 vaccines is higher than the background CVST incidence of 1.32–1.57/100,000/year.5,6 As the world continues its vaccination efforts, the occurrence of CVST should be kept in mind as a possible significant side effect. However, in line with recommendations7,8 from various major committees, its rarity suggests that the benefits of CO- VID-19 vaccines still outweigh their risks. Worldwide moni- toring and data collection would be highly prudent as we con- tinue to administer mRNA and other vaccines in efforts to end the pandemic. Ethics Statement Informed consent was obtained from the patient. Availability of Data and Material Data sharing not applicable to this article as no datasets were generated or analyzed during the study. ORCID iD Newman Cheng https://orcid.org/0000-0003-1692-5326 574 J Clin Neurol 2021;17(4):573-575 Conflicts of Interest The author has no potential conflicts of interest to disclose. Funding Statement None REFERENCES 1. Schultz NH, Sørvoll IH, Michelsen AE, Munthe LA, Lund-Johansen F, Ahlen MT, et al. Thrombosis and thrombocytopenia after ChAdOx1 nCoV-19 vaccination. N Engl J Med 2021;384:2124-2130. 2. See I, Su JR, Lale A, Woo EJ, Guh AY, Shimabukuro TT, et al. US case reports of cerebral venous sinus thrombosis with thrombocytopenia after Ad26.COV2.S vaccination, March 2 to April 21, 2021. JAMA 2021;325:2448-2456. 3. Cines DB, Bussel JB. SARS-CoV-2 vaccine-induced immune throm- botic thrombocytopenia. N Engl J Med 2021;384:2254-2256. 4. Idiculla PS, Gurala D, Palanisamy M, Vijayakumar R, Dhandapani S, Nagarajan E. 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