Renal tubular acidosis type IV as a complication of lupus nephritis.

Renal tubular acidosis (RTA) is a rare complication of renal involvement of systemic lupus erythematosus (SLE). We describe a 24-year-old male with type IV lupus nephropathy as a presenting manifestation of SLE. He presented with improvement of renal function following induction therapy with three pulses of methylprednisolone and 500 mg biweekly pulses of cyclophosphamide. However, a week after the first pulse of cyclophosphamide, the patient presented with a significant increase in legs edema and severe hyperkalemia. Type IV RTA associated with hyporeninemic hypoaldosteronism was suspected in the presence of metabolic acidosis with a normal anion gap, severe hyperkalemia without worsening renal function, and urinary pH of 5. RTA was confirmed with a transtubular potassium concentration gradient of 2 and low levels of plasma aldosterone, renin, angiotensin II, and cortisol. Intravenous bicarbonate, high-dose furosemide, and fludrocortisone were administered with normalization of potassium levels and renal function.