Clinical research study
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Mild Chronic Hyponatremia Is Associated With Falls, Unsteadiness, and Attention Deficits

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Abstract

Objective

The study objective was to determine the eventual consequences (falls, unsteadiness, and cognitive impairment) of mild chronic hyponatremia, which is generally considered as asymptomatic.

Methods

In a case-control study, we focused on the incidence of falls among 122 patients (mean age 72 ± 13 years) with asymptomatic chronic hyponatremia (mean serum sodium concentration [SNa] 126 ± 5 mEq/L), who were admitted to the medical emergency department, compared with 244 matched controls. To explore the mechanisms of the excess of falls, we prospectively asked 16 comparable patients (mean age 63 ± 15 years; SNa ± 2 mEq/L) to perform 8 attention tests and a gait test consisting of 3 steps “in tandem,” in which we measured the “total traveled way” by the center of pressure or total traveled way. Thereafter, the patients were treated and tested again (50% of the patients were tested first with normal SNa to avoid learning biases).

Results

Epidemiology of falls: Twenty-six patients (21.3%) of 122 were admitted for falls, compared with only 5.3% of the control patients (adjusted odds ratio: 67; 95% confidence: 7.5-607; P <.001). The frequency of falls was the same regardless of the level of hyponatremia. Gait: The total traveled way by the center of pressure significantly increased in hyponatremia (1336 ± 320 mm vs 1047 ± 172 mm with normal SNa; P = .003). Attention tests: The mean response time was 673 ± 182 milliseconds in hyponatremia and 615 ± 184 milliseconds in patients with normal SNa (difference: 58 milliseconds, P <.001). The total error number in hyponatremia increased 1.2-fold (P = .001). These modifications were comparable to those observed after alcohol intake in 10 volunteers.

Conclusions

Mild chronic hyponatremia induces a high incidence of falls possibly as the result of marked gait and attention impairments. Treating these patients might prevent a considerable number of hospitalizations.

Section snippets

Subjects and methods

We reviewed the occurrence of falls in 151 consecutive hyponatremic patients without peripheral edema or ascites who arrived at the medical emergency department and were admitted to the medical ward of a general hospital in Brussels during a period of 3 years. Only patients with SNa between 115 and 132 mEq/L were included. We excluded patients with a history of cardiac failure, cirrhosis, or nephrotic syndrome. No patient presented with any acute organic brain disease. Patients with suspected

Evaluation of gait

Tandem gait parameters were acquired and analyzed with a pressure-sensitive calibrated platform (Footscan, RSScan International, Olen, Belgium), which evaluates the patient’s balance performance6, 7 on the basis of the recorded displacement of the center of pressure (ie, the projection of the center of gravity on the ground) (Figure 1). We asked patients to perform 3 stereotyped steps on the platform, “in tandem,” with eyes open. TTW was obtained in triplicate (TTW being the “total traveled

Attention tests

Among a battery of attentional tests, we chose very simple tests. The tasks consisted of easily distinguishable stimuli that the patients react to by a simple motor response. Eight different visual and auditory tests were performed with computerized standardized attentional tasks (Test for Attentional Performance).8, 9, 10 Subjects were isolated in a quiet room and seated in front of a 14-inch computer screen at a viewing distance of 40 to 50 cm. We made sure that the patients had as much

Statistical analysis

Comparisons between the 122 hyponatremic patients and 244 control subjects were made with the Fisher 2-tailed exact test. Adjusted odds ratios were obtained with the use of a conditional logistic-regression model to determine independent associations between the presence of falls and hyponatremia after controlling for covariates. Covariates were identified if the P value was less than .05 on the basis of the univariate analyses. Age and sex were also included in the multivariable conditional

Results

The 151 consecutive hyponatremic patients without edema (84 females and 67 males; mean age: 70 ± 14 years; mean plasma sodium: 125 ± 5 mEq/L) were classified in different etiologic groups according to their response to the infusion of 2 L of isotonic saline over 24 hours 11 as follows: 58 patients with the SIADH, 30 patients with diuretic-induced hyponatremia, 26 patients with salt depletion, 25 patients with polydipsia-hyponatremia syndrome, and 12 patients with miscellaneous causes of

Gait tests

In the tandem eyes open test (Figure 1), TTW was studied. The center of pressure (TTW) of the patients changed 1336 ± 320 mm in hyponatremia versus 1047 ± 172 mm (P = .003; Table 3). There was no statistical difference between the values observed in our patients (after correction of SNa) compared with the control group.

Alcohol tests

The mean blood alcohol content was estimated as 0.6 ± 0.2 g/L. The TTW did not statistically increase after acute alcohol intake (from 1028 mm to 1095 mm, P = .06, (Table 3).

Attention tests

Sixteen patients were recruited for the attention tests. Their mean age was 63 ± 15 years and did not differ significantly from the large group of 122 patients. The mean level of hyponatremia was 128 ± 3 mEq/L. The median response time for each test (Table 4) was determined in hyponatremia and with normal SNa. All tests tended to reveal greater latencies in hyponatremia. Most alterations appeared in the following tests: Phasic Alert (which is one of the strongest markers of general attention

Discussion

The study of falls is intriguing and has great potential clinical significance for all hyponatremic patients. We found that patients with moderate chronic hyponatremia fall dramatically more frequently than controls. In addition, our research shows that clinically asymptomatic patients with chronic hyponatremia reveal instability in dynamic tasks and attentional impairments in sensitive tests. To our knowledge, this is the first study addressing falls, gait, and attention in this population.

Acknowledgments

We are indebted to A. Destrebecqz, P. Féry, T. Claes, J-C Bier for helpful discussions; and A. Hedeshi, A. Soupart, P. Tughendaft, F. Vandergheynst, and O. Xhaet for referring patients. We thank Professor Chr. Melot for statistical advice. We thank C. Huyssen, P. Brennan, and C. Howells for careful typographic help.

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Supported by a grant from the Fonds National de la Recherche Scientifique, convention N°3.4509.03. The authors’ work was independent of the funders.

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