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Sjogren Renal Disease — SCE Rheumatology MCQ

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HardConnective Tissue DiseaseSjogren Renal DiseaseSCE Rheumatology

A 48-year-old woman with primary Sjögren disease has hypokalaemia, hyperchloraemic normal-anion-gap metabolic acidosis and preserved glomerular filtration. Her urine pH remains 6.3 during systemic acidosis, and renal ultrasonography shows nephrocalcinosis. Which pathophysiological mechanism best explains this renal tubular defect?

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Correct answer: E — Autoimmune loss of distal H+-ATPase expression, often with tubulointerstitial nephritis

This is type 1 distal renal tubular acidosis: hypokalaemic normal-anion-gap acidosis with an inappropriately alkaline urine and nephrocalcinosis despite preserved glomerular filtration. In Sjögren disease, autoimmune injury causes dysfunction or loss of acidification transporters in distal-nephron alpha-intercalated cells, particularly vacuolar H+-ATPase; AE1 and other transporters may also be affected. This commonly accompanies lymphocytic tubulointerstitial nephritis, although transporter loss and distal RTA can precede overt histological inflammation. Urate deposition causes obstruction, while amyloidosis and immune-complex glomerulonephritis primarily produce glomerular findings such as proteinuria or haematuria. Proximal tubular toxicity causes type 2 RTA, in which urine can become appropriately acidic after serum bicarbonate has fallen.

Reference: Ungureanu O, Ismail G. Distal Renal Tubular Acidosis in Patients with Autoimmune Diseases—An Update on Pathogenesis, Clinical Presentation and Therapeutic Strategies. Biomedicines. 2022;10:2131. https://pubmed.ncbi.nlm.nih.gov/36140232/