A study conducted by researchers in Seoul, Korea and Geoje, Korea found that hyponatremia is reflective of disease activity in children and adults with systemic lupus erythematosus (SLE).
“The incidence and clinical significance of hyponatremia has not been studied in rheumatic diseases including SLE, and only some case reports of hyponatremia have been reported in SLE,” wrote Jae Il Shin, MD, PhD, from Yonsei University College of Medicine and Severance Children’s Hospital in Seoul, Korea and colleagues. “[There has also] been no report describing the relationship between the degree of hyponatremia and the disease activity in both childhood and adulthood SLE.”
The researchers therefore aimed to evaluate the clinical and laboratory characteristics associated with disease activity in children and adults with SLE, and to determine whether decreased serum sodium concentration could be associated with SLE disease activity.
The researchers retrospectively analyzed data from 37 children (4 boys, 33 girls) who had been diagnosed with SLE at Severance Children’s Hospital from 1991 to 2010. Laboratory exams were collected twice, first during staging of disease activity, and once at the follow-up visit 22.2 ± 28.3 months later (range 1–123 months). The patients were divided into 2 groups: group I (n = 11 samples, hyponatremia) and group II (n = 63 samples, no hyponatremia).
Out of 166 adult patients with SLE who were followed up at Ajou University, 84 whose serum sodium levels were available were also included in the study (mean age: 34.4 ± 12.1 years [range 16–69 years]; 8 men, 76 women).
The researchers demonstrated that hyponatremia was associated with decreased complement 3 (C3), increased erythrocyte sedmintation rate (ESR), and increased SLE disease activity index (SLEDAI), all of which reflect disease activity in SLE. In addition, serum sodium levels appeared to be negatively correlated with interleukin(IL)-6 levels (r = −0.317, P = .003).
“Although the exact mechanism of hyponatremia in [patients experiencing flares associated with SLE] is not established yet, we speculate that inflammation can be one of the mechanisms in the pathogenesis of hyponatremia in SLE patients,” the researchers wrote.
In this particular cohort of children with SLE, decreased serum chloride was found to be an independent risk factor for future development of hyponatremia.
“Urinary loss of sodium chloride could cause hyponatremia and hypochloremia, and it can be caused by renal tubular damage or increased renal sodium loss by a reduction in renal tubular sodium absorption in inflammatory conditions.”
Summary & Clinical Applicability
Hyponatremia in this cohort of patients was associated with decreases in complement levels and increases in ESR and SLEDAI scores, reflecting a relationship between serum sodium and SLE disease activity.
According to the researchers, “the current data are noteworthy because we … showed that hyponatremia reflected disease activity of SLE in 2 independent cohorts of children and adults with SLE.”
Further research is needed to evaluate the exact molecular mechanism of hyponatremia in SLE, and to determine whether these findings are relevant in a large cohort of SLE.
Limitations & Disclosures
The study has some limitations, including a small sample size due to the relative rarity of SLE in Korea and the retrospective study design. A follow-up study would be able to assess the relationship between serum complement and interleukin levels and other measures of SLE disease activity to determine which factors most closely associated with severity.
Shin IL, Park SJ, Suh CH, Lee GH, et al. Hyponatremia in patients with systemic lupus erythematosus. Sci Rep. 2016; doi: 10.1038/srep25566.