Tuberculous meningitis: does lowering the treatment threshold result in many more treated patients?

To determine how many more patients would be treated when lowering the treatment threshold for tuberculous meningitis.

From 1989 to 2004 findings of patients with symptoms lasting more than 1 week and inflammatory changes of cerebrospinal fluid (CSF) were collected. Several models of latent class analysis were tested. Cumulative numbers of cases were plotted against different cut-offs for post-test probability.

In a cohort of 232 patients the prevalence of tuberculous meningitis (TBM) was estimated at 79.8% (95% CI. 67,0-88,1); probabilities above 80% were reached in 73% of patients. Lowering this threshold from 80% to 20% would add 14% more patients to be treated, for a total of 87%. A further lowering of the threshold to 5% would imply 5% more patients to be treated, bringing the cumulative number to 92%. The difference of lowering the threshold from 80% to 5% was 19%.

In this setting, at least 75% of patients showing suggestive symptoms for more than a week and CSF changes very probably had TBM. The number of patients that should be treated does not increase linearly when lowering the threshold.