In the linked study (doi:10.1136/bmj.c4451), Vinnard and colleagues assess whether initial resistance to isoniazid is associated with death during the treatment of tuberculous meningitis.1 Central nervous system tuberculosis accounts for about 1% of the estimated 9.4 million annual cases of tuberculosis worldwide.2 Tuberculous meningitis is a medical emergency and in the past was usually lethal, although better chemotherapy, starting with streptomycin in 1947, has improved survival dramatically.3 Nonetheless, even with modern treatment almost a third of patients die, and case fatality rate approaches two thirds in patients with HIV.4 Half of those who survive have neurological sequelae.5

Because delayed treatment increases case fatality rate,6 it is unfortunate that tuberculous meningitis is so difficult to diagnose. In high income countries, patients may die because of the delay in diagnosis—culture of Mycobacterium tuberculosis requires special medium and takes many weeks. In developing countries, clinicians make a presumptive diagnosis by combining clinical data and simple laboratory results,7 but they struggle to confirm the diagnosis …