Serum sodium and osmolal changes in tuberculous meningitis.

Twenty children from 2 months to 7 years (mean age 2.74 years +/- 1.62) diagnosed to have tuberculous meningitis (TBM) were evaluated for serial serum sodium levels and osmolality of cerebrospinal fluid (CSF), serum and urine on admission and the results compared with 20 age and nutritionally matched controls, and these investigations repeated on day 3 and day 10. Mean serum sodium levels (130.7 +/- 6.26 mEq/L), and osmolality of CSF (272.0 +/- 7.0 mOsm/kg) and serum (275.5 +/- 6.09 mOsm/kg) were significantly lower (p < 0.001) than in controls. Hyponatremia was detected in 65% of cases on admission, 47% on day 3 and in 30.8% on day 10. All the patients with hyponatremia had biochemical evidence of syndrome of inappropriate secretion of antidiuretic hormone (SIADH) on admission. Incidence of SIADH gradually decreased to 41.2% on day 3 and 15.4% on day 10. In some of the cases serum sodium levels and osmolality of serum and CSF took about 3 weeks to return to normal. CSF osmolality was lower than concomitant serum osmolality in patients as well as in controls. In patients with SIADH, CSF osmolality followed the same trend as serum values and returned to normal in 2-3 weeks. Overall mortality was 25%. Two out of 3 patients who expired during first 3 days had SIADH but in those cases who survived there was no correlation with degree of meningeal inflammatory changes or ultimate outcome. SIADH is commonly associated with TBM and should be diagnosed early in order to modify the fluid therapy in these cases.(ABSTRACT TRUNCATED AT 250 WORDS)