Psychomotor Deficits Associated With Hyponatremia: A Retrospective Analysis

Abstract

Hyponatremia (serum sodium concentration [Na+] < 136 mEq/L) is a potentially life-threatening condition. Recent evidence (Renneboog, Musch, Vandemergel, Manto, & Decaux, 2006) shows that even mild hyponatremia is associated with disorders of balance/gait. This retrospective analysis explored the influence of serum [Na+] on neuropsychological (NP) measurements at baseline from 44 patients with chronic hyponatremia who participated in an efficacy and safety study of an experimental compound over a decade ago. Group mean serum [Na+] was 124.8 ± 4.9 mEq/L. Age-adjusted partial correlations were computed between serum [Na+] and NP measurements, 39% of which were statistically significant--all involving psychomotor functioning. These findings replicate and extend previous observations that psychomotor deficits are, at least in part, associated with hyponatremia in these patients. While chronic hyponatremia is known to have deleterious effects on quality of life, motor and gait disturbances represent manifestations of mild hyponatremia that have until now gone unrecognized. A new class of medication, vasopressin antagonists, has been shown to correct hyponatremia. It will be important to explore the effects of correcting hyponatremia on psychomotor functioning in individuals with hyponatremia.

Motor Deficits Associated With Mild, Chronic Hyponatremia: A Factor Analytic Study

“…Only the FT (dominant hand) and SRT tasks test-independently of other abilities-"pure" motor ability (i.e., the FT task is a measure of self-directed motor speed and records the amount of finger taps per minute, not directed by computer-generated tones, or fixed intertone intervals; the SRT task records the speed of reaction by pressing a button in response to a computergenerated stimulus). As previously stated, though motor and psychomotor impairment was mentioned in Josiassen et al (2012), it was unclear what specific variables were the primary contributors to the association with serum [Na+]. To our knowledge, this is the first study to address specific impairment distinguishing between motor and psychomotor deficits.…”

“…The battery included a variety of motor, psychomotor, cognitive, and intelligence tests and was administered by a trained psychometrist at each site. The entire battery took approximately 2.5 hr to administer (for a full description of the neuropsychological battery, see Josiassen et al 2012). Ultimately, 41 of the original 44 subjects were included in the present analysis of baseline data (see Table 1 for subject demographics and clinical characteristics).…”

“…Though within the motor realm, these tasks interweave motor and psychomotor components and cannot be unambiguously identified or interpreted without further analysis. Only Josiassen et al (2012) reported deficits in "pure" motor functioning (simple reaction time) to be associated with CHN. However, due to the amount of significant associations between serum [Na+] and individual neuropsychological raw scores produced from their analyses (7 of 18 correlation coefficients achieved statistical significance), the authors did not isolate "pure" motor deficits from psychomotor or other cognitive deficits.…”

“…Thus the purpose of the present study was to expand on the work of Josiassen et al (2012) using factor analytic procedures to disentangle the putative orthogonal factors present in the previously reported neuropsychological data. It was anticipated that a more "pure" motor function factor would be identified.…”

American Society of Nephrology Quiz and Questionnaire 2015

“…More recently, however, chronic hyponatremia has been associated in observational studies with both an increased incidence of falls (approximately four-fold higher than in a control population) as well as a higher bone fracture rate (approximately three-fold higher than in a control population) and higher incidence of osteoporosis (32,33). The explanations for these findings are: (1): hyponatremia is associated with significant gait and psychomotor abnormalities leading to unsteadiness (32,34), and (2) hyponatremia, through unclear mechanisms, has effects on both osteoclasts and osteoblasts, which decrease bone integrity and strength (35,36). Thus, the combination of an unsteady gait and osteoporosis explains the augmented risk of both falls and fractures in patients with chronic hyponatremia.…”