Hyponatremia in systemic lupus erythematosus patients: Relation to disease activity and fatigue

Abstract

Aim of the workTo investigate the relation of hyponatremia to disease activity and fatigue in systemic lupus erythematosus (SLE) patients. Patients and methodsThe present study included 30 SLE patients with hyponatremia and 70 with normal serum sodium (Na) level. SLE disease activity index and the Functional Assessment of Chronic Illness Therapy (FACIT)-Fatigue score were assessed. ResultsThe gender, age and disease duration of SLE patients with hyponatremia (26 females and 4 males; mean age 37.8 ± 9.3 years, 10.9 ± 5.1 years) were comparable with those without (60 females and 10 males; 36.9 ± 11.8 years, 11.1 ± 6.02; p = 0.71 and p = 0.9 respectively). SLE patients with hyponatremia showed significantly increased SLEDAI (14.2 ± 3.85 vs 3.86 ± 3.59; p < 0.001), ESR (55.2 ± 18.2 vs 14.70 ± 3.5 mm/1st h; p < 0.001) and CRP (30.97 ± 4.4 vs 5.17 ± 2.6 mg/dl; p < 0.001) and lower FACIT-Fatigue (21.99 ± 2.1 vs 35.87 ± 4.81; p < 0.001) compared to patients without. Serum Na levels significantly correlated with the FACIT-fatigue score (r = 0.99, p < 0.01), platelets (r = 0.22; p = 0.03), white blood cells count (r = 0.31, p < 0.001) and inversely with SLEDAI (r = −0.27, p = 0.01), ESR (r = −0.71; p < 0.001), CRP (r = −0.86, p < 0.001), anti-ds-DNA (r = 0.54, p < 0.001), C3 (r = −0.29, p = 0.01) and C4 (r = −0.2, p = 0.04). On regression, CRP (β = 0.3), SLEDAI (β = 0.28) and consumed C4 (β = −0.07) were significant independent risk factors for hyponatremia (p < 0.0001, p = 0.0005, p = 0.02 respectively). The optimal cut-off values to predict hyponatremia was a SLEDAI score ≥11 (90% sensitivity and 96% specificity), and ESR ≥ 17.5 mm/1st h (100% sensitivity and 80% specificity) and a CRP of ≥10.5 mg/dl (100% sensitivity and 97% specificity). ConclusionHyponatremia in SLE patients is associated with higher disease activity and more perceived fatigue. Hyponatremia could reflect severe inflammation and could be considered as one of the predisposing factors of fatigue.