Distal Renal Tubular Acidosis Associated with Autoimmune Diseases: Reports of 3 Cases and Review of Mechanisms.

BACKGROUND Distal renal tubular acidosis (dRTA) is a defect in the urinary acidification process that limits the elimination of protons [H+] by alpha intercalated cells in the collecting tubules, with consequent metabolic acidosis with a normal plasma anion gap. The relationship between this tubulopathy and immune-mediated diseases like Sjögren syndrome, rheumatoid arthritis, autoimmune hepatitis, primary biliary cirrhosis, systemic lupus erythematosus, and thyroiditis is well known. Further, the pathophysiological mechanisms are diverse, but, unfortunately, many are not yet fully understood. We report 3 cases of dRTA in patients with different autoimmune diseases and review the pathophysiological mechanisms already described. CASE REPORT The first case involved a 29-year-old woman with autoimmune hepatitis. She had metabolic acidosis with persistent hypokalemia, and a kidney stone was also identified. The second case involved a 67-year-old woman diagnosed with rheumatoid arthritis. She had metabolic acidosis with hypokalemia. The third case involved a 30-year-old woman with Sjögren syndrome and persistent metabolic acidosis. In addition to the presence of metabolic acidosis with a normal plasma anion gap, all 3 patients exhibited urine with a supraphysiologic pH (above 5.3). CONCLUSIONS Autoimmune diseases may be associated with deficits in urinary acidification with consequent metabolic acidosis and, therefore, systemic repercussions. This association must be remembered and researched because correct diagnosis and treatment will serve to reduce complications.