Blood-brain barrier permeability in survivors of immune-mediated thrombotic thrombocytopenic purpura: a pilot study.

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a rare, life-threatening disorder of systemic microthrombosis and organ ischemia. The etiology of chronic cerebrovascular outcomes in iTTP survivors is largely unknown. In this pilot study, we measured blood-brain barrier (BBB) permeability in iTTP patients at the start of remission and 6 months later. This prospective pilot study included 7 adult patients with incident iTTP. Eligibility criteria included ADAMTS13 activity <10% and detectable inhibitor at diagnosis. Patients were recruited from London Health Sciences Centre in Canada (2017-2019) within 3 days of hospital admission and followed for 6 months after remission (defined as normalization of platelet count and lactate dehydrogenase with no clinical signs or symptoms of microvascular injury for more than 30 days after the last plasma exchange). All patients had cerebral CT perfusion scans with BBB permeability surface product measurements. Patients (5 women, 2 men) had a mean age of 48 years (range 21-77). At diagnosis, patients had a mean platelet count of 22 (standard deviation [SD] 25) x109/L. At the start of remission, mean BBB permeability surface product was 0.91 (0.30) mL/min/100g. Six months later, the mean permeability surface product was 0.56 (0.22) mL/min/100g, with mean difference: -0.312 mL/min/100g (95% confidence interval: -0.4729 to -0.1510; p=0.0032). In this pilot study of iTTP patients, pathologically increased BBB permeability was evident and, though there was some improvement, this persisted 6 months after remission. Future work will explore the chronicity of these findings and their clinical implications.