Incidence of thrombocytopenia-associated cerebral venous sinus thrombosis: a population-based study.

Objectives: The identification of SARS-CoV-2 vaccine-induced immune thrombotic thrombocytopenia (VITT) followed the recognition of a hitherto uncommon clinical syndrome frequently associated with cerebral venous sinus thrombosis (CVST), termed 'thrombosis with thrombocytopenia' syndrome (TTS). While anecdotally recognised as rare, the background incidence of TTS is unknown. We therefore aimed to investigate the background incidence of CVST with TTS in a large, well-defined population-based CVST cohort. Methods: We performed an analysis of our previously obtained retrospective population-based cohort of patients with CVST from Adelaide, Australia (2005-2011, comprising an adult population of 953 390) to identify the background incidence of CVST associated with TTS. Results: Among 105 people with CVST, the background population-based incidence of TTS-associated CVST was 1.2 per million per year (95% CI 0.5 to 2.4). A single case of a severe CVST VITT-like syndrome with multiorgan thrombosis was identified, occurring 3 weeks postrotavirus infection. Conclusions: In our population-based study, the background incidence of CVST with associated TTS was very low, and the sole clinically severe case with multiorgan thrombosis occurred following a rotaviral precipitant. Our study establishes a benchmark against which to measure future potential 'TTS' clusters and suggests that viruses other than adenovirus may trigger this syndrome.