Idiopathic Hypokalemia in Lupus Nephritis: A Newly Recognized Entity

Abstract

Background:Various causes of hypokalemia from renal potassium wasting, including distal renal tubular acidosis, have been described in lupus nephritis (LN). We report a phenomenon of otherwise unexplained hypokalemia among a population with LN. Methods:From our population of 403 patients with LN, we identified a cohort of 20 patients with idiopathic hypokalemia (HK), defined by serum potassium < 3.5 mmol/L without any apparent explanation. This cohort is compared to 90 LN controls (CON) and 10 LN patients with distal renal tubular acidosis (RTA) from the same population. Results:The HK cases had lower median serum potassium compared to CON and RTA subjects (3.26 vs 4.00 vs 3.75 mmol/L, respectively; p < 0.001). The median serum bicarbonate was normal in HK and CON but low in RTA (26.0 vs 25.0 vs 19.4 mmol/L; p < 0.001). The median urine pH was abnormally high only in the RTA group (6.00 vs 6.25 vs 6.67; p = 0.012). The median serum magnesium was modestly lower in HK compared to the CON and RTA groups (1.73 vs 2.00 vs 1.85 mg/dL; p = 0.002). While both HK and RTA showed a higher rate of seropositivity than CON for anti-Ro/SSA (79% and 80% vs 37%, respectively; p < 0.001), only HK revealed a higher rate of seropositivity than CON for anti-RNP (84% vs 42%; p = 0.003) and only RTA showed a higher rate of seropositivity than CON for anti-La/SSB (40% vs 12%; p = 0.046). Conclusions:A syndrome of idiopathic hypokalemia was revealed in 20/403 (5%) of patients within our LN population and proved to be distinct from the renal tubular acidosis that occurs in LN. Furthermore, it was associated with a distinct pattern of autoantibodies. We speculate that idiopathic hypokalemia is the result of a novel target of autoimmunity in LN affecting renal tubular potassium transport.

Still Learning from Our Patients: Hypokalemia in Patients with Lupus Nephritis

“…Since inception, the clinic has cared for 435 patients with lupus nephritis, and an additional 464 patients with other glomerular diseases (K. Sambandam, personal communication). In this issue of Kidney360 , Adomako and colleagues (1) draw on their clinical experience caring for this large population of patients to describe a new entity, idiopathic hypokalemia in lupus nephritis. They identify 20 patients with this disorder, who do not have evidence of other suspected or known causes of hypokalemia, for a prevalence of 5%.…”