Venous sinus thrombosis after the first dose of Pfizer BioNTech vaccine.

mRNA vaccines including Pfizer BioNTech and Moderna have categorically been considered safe when it comes to preventing COVID-19. However, there is still a small associated risk of thromboembolic phenomenon including venous sinus thrombosis with it and our case report highlights one.We describe a patient who developed severe progressive headache, tinnitus and visual disturbance symptoms post-Pfizer-SARS-CoV-2 vaccination. His medical history included essential tremors, hypertension, type 2 diabetes mellitus, chronic kidney disease stage 3, anxiety, depression and long-term catheterisation. Systemic examination revealed hypotonia, generalised reduced power and central diplopia along with peripheral visual field defect in the left eye. He was extensively investigated, the COVID-19 PCR test was negative and all routine blood tests were in the normal range except a marginally raised D-dimer of 779 ng/mL. CT head was unremarkable. He was also tested for myasthenia gravis; however, acetylcholine receptors antibodies were negative and nerve conduction studies were normal. Subsequent MRI of the brain with venography confirmed venous sinus thrombosis. A 24-hour Holter monitoring test did not reveal any cardiac rate or rhythm abnormality. He was treated with apixaban as per a neurologist's advice. His clinical condition started to improve and was later discharged from the hospital with an outpatient neurologist clinic follow-up.