Hyperkalemia in type 4 renal tubular acidosis associated with systemic lupus erythematosus

Renal tubular acidosis (RTA) is a normal anion gap metabolic acidosis that manifests with insufficiency of hydrogen ion excretion or bicarbonate (HCO₃) reuptake as a result of renal tubular dysfunction independent of glomerular filtration rate. Hypokalemic RTA subtypes co-existing with autoimmune diseases particularly appear in Sjogren's syndrome, but rarely in systemic lupus erythematosus (SLE). Type 4 RTA associated with hyperkalemia is very rare during the course of SLE and hence has been scarcely reported in the literature. Here, we report a 42-year-old patient for whom regular follow-up was ongoing due to class IV lupus nephritis when she developed hyperkalemia. The patient had normal anion gap hyperkalemic metabolic acidosis and her urine pH was 5.5. Type 4 RTA was considered and, therefore, tests for renin and aldosterone levels were requested, which revealed that renin was suppressed and aldosterone was decreased. Upon diagnosis of SLE-associated type 4 RTA, short-term oral HCO₃ and fludrocortisone were initiated. Potassium (K) and HCO₃ levels improved at day 15 of therapy. In this review, we analyzed our case along with five other reports (a total of seven cases) of SLE-associated type 4 RTA we identified through a literature search. We wanted to highlight RTA for differential diagnosis of hyperkalemia emerging during SLE/lupus nephritis and we also discussed possible underlying mechanisms.