A study of atrial and brain natriuretic peptides in tuberculous meningitis and acute encephalitis

To report atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) levels in patients with tuberculous meningitis (TBM) and acute encephalitis syndrome (AES), and evaluate their relationship with hyponatraemia.

Consecutive patients with TBM and AES were included in the study. Hyponatraemia was categorised as cerebral salt wasting (CSW), syndrome of inappropriate secretion of antidiuretic hormone (SIADH) and a miscellaneous group based on clinical and laboratory criteria. Serum ANP and BNP levels were measured upon hospital admission, at the time of diagnosis of hyponatraemia and upon correction of hyponatraemia. Outcome at 3 months was assessed using the modified Rankin scale (mRS) as good (mRS 2) and poor (mRS >2).

There were 67 patients with TBM and 77 with AES. Hyponatraemia was more common in TBM than in AES (65.7% vs. 27%, P < 0.01). Forty-one (63.1%) patients had CSW, 6 (9.2%) SIADH and 18 (27.7%) had miscellaneous causes of hyponatraemia. During hyponatraemia, ANP (180 ± 45 vs. 106 ± 32 pg/ml, P < 0.01) and BNP (263 ± 118 vs. 163 ± 91 pg/ml, P  0.01) levels were significantly increased compared with baseline, and remained high even after Na+ correction.

ANP and BNP levels were increased during hyponatraemia and remained high even after correction of hyponatraemia in TBM and AES, especially in patients with CSW. However, ANP and BNP levels could not be used to differentiate CSW from SIADH.