Cerebral Hemodynamics and Stroke in HIV-associated TB Meningitis.

Abstract Tuberculous meningitis (TBM) disproportionally affects people in low- and middle-income countries and is associated with high morbidity and mortality. Stroke is a common complication in TBM and can lead to severe irreversible neurological disability. Studies on TBM-associated stroke pathology, however, have focused primarily on HIV-uninfected individuals. The overall objective of this proposal is to use transcranial doppler and brain imaging to understand changes in cerebral blood vessels and cerebral blood flow in order to determine changes in cerebrovascular responsiveness, characterize patterns of stroke, and describe long-term neurocognitive outcomes in HIV-associated TBM. The central hypothesis is that in HIV-infected individuals, TBM causes extensive cerebral vascular narrowing and impaired cerebrovascular responsiveness, decreased cerebral blood flow, and ultimately stroke. The central hypothesis will be tested by pursuing three specific aims: 1) describe changes in cerebrovascular responsiveness in HIV-associated TBM; 2) characterize the patterns of stroke in HIV-associated TBM and determine whether it is associated with vasculopathy and/or impairments in cerebrovascular responsiveness; and 3) determine if impaired cerebrovascular responsiveness predicts long- term neurological outcome in HIV-associated TBM. Under Aim 1, transcranial doppler will be used to take repeated measurements of the middle cerebral artery flow velocity and pulsatility index. A subset of study subjects will also have dynamic measurements made in response to stimuli (inhaled CO2, changes in blood pressure, and motor tasks). We will determine whether cerebrovascular responsiveness is impaired in HIV- associated TBM by comparing measurements to those of control patients with no neurological infection. Under Aim 2, all study subjects will have a brain MRI performed within the first 2-weeks of TBM treatment to identify the presence of a cerebral artery stroke and the associated cerebral artery territory. We will compare TCD readings between participants with or without stroke. Under Aim 3, we will examine how TCD measurements at study enrolment relate to the results of neurocognitive testing at month 2 and functional assessment at month 6. Ultimately, the long-term goal of the proposal is to describe how impaired cerebrovascular responsiveness in HIV-associated TBM contributes to the development of strokes and resulting neurocognitive impairment and disability. The research proposed in this application is innovative because it incorporates the use of transcranial doppler at the bedside, to be used in real time, in the care of subjects with TBM. The proposed research is significant because it is expected to provide strong scientific justification for the development of future clinical trials testing targeted interventions to improve cerebrovascular responsiveness and prevent the development of strokes in HIV-associated TBM. Ultimately, such knowledge has the potential of preventing the development of irreversible neurological injury and improving both short and long-term outcomes.