Background:  In clinical practice, hyponatraemia was frequently found in patients with hydrocephalus. We conducted this study to determine the prevalence and risk factors for hyponatraemia in patients with normal pressure hydrocephalus (NPH).

Methods:  We retrospectively reviewed all patients with NPH who were admitted to China Medical University Hospital between 1998 and 2006. Hyponatraemia was defined as a plasma sodium concentration < 135 mEq/l on admission. Possible risk factors between patients with and without hyponatraemia were analysed using Student’s t-test or χ2 test. The association between hyponatraemia and possible factors was analysed using multivariate logistic regression. The odds ratio was calculated to determine the effect of possible risk factors.

Results:  A total of 146 patients (84 men and 62 women) who had NPH with a mean age of 66.1 ± 15.9 years old were reviewed and 33 (22.6%) patients were found having hyponatraemia. Patients who developed hyponatraemia had a significantly higher prevalence of hypertension, use of nasogastric tube (NG), bed-ridden status and fever. In multivariate logistic regression, the presence of hypertension and the use of NG were two important risk factors for hyponatraemia. The odds ratio (95% CI) for hypertension and NG were 2.604 (95% CI: 1.136–5.967, p = 0.024) and 7.179 (95% CI: 2.3–22.409, p = 0.001) respectively.

Conclusion:  Hyponatraemia is not uncommon in patients with NPH. Physicians should be aware of this complication and obtain necessary laboratory examination for early detection of hyponatraemia.