The primary objective is to determine whether Leukotriene A4 hydrolase (LTA4H) genotype, defined at randomisation, determines dexamethasone's clinical effectiveness when added to the first 6-8 weeks of anti-tuberculosis treatment of TBM. The investigators will conduct a LTA4H genotype stratified, parallel group, randomised, double blind, placebo-controlled multi-centre Phase III non-inferiority trial evaluating dexamethasone versus placebo for 6-8 weeks in addition to standard anti-tuberculosis drugs.