ADA and lymphoma: Although most recent studies have focused on distinguishing between TBM and meningitis of other bacterial or infectious origins, an early 1990s study already reported that the concentration of CSF-ADA could be elevated in patients with lymphoma (5 patients, range, 4–25 IU/L) like in TBM (3 patients, range, 20–23 IU/L) (Pettersson et al., 1991).