Renal tubular acidosis without interstitial nephritis in Sjögren's syndrome: a case report and review of the literature

Abstract

Background: Renal tubular acidosis is the principal clinical feature associated with tubulointerstitial nephritis in patients with primary Sjögren's syndrome. Renal tubular dysfunction due to interstitial nephritis has been considered the underlying pathophysiology connecting renal tubular acidosis and primary Sjögren's syndrome. However, the detailed mechanisms underlying the pathophysiology of renal tubular acidosis in primary Sjögren's syndrome is not fully understood.

Case presentation: A 30-year-old woman was admitted with complaints of weakness in the extremities. The patient was hospitalized thirteen years earlier for similar issues and was diagnosed with hypokalemic paralysis due to distal renal tubular acidosis with primary Sjögren's syndrome. This diagnosis was based on a positive Schirmer's test. Besides, anti-Sjögren's syndrome-related antigen A was also detected. Laboratory tests indicated distal RTA; however, a renal biopsy showed no obvious interstitial nephritis. Laboratory tests conducted during the second admission indicated distal renal tubular acidosis. Therefore, a renal biopsy was performed again, which revealed interstitial nephritis. Histological analysis of acid-base transporters revealed the absence of vacuolar type H⁺-ATPases in the collecting duct. The vacuolar type H⁺-ATPase was also absent in the past renal biopsy, suggesting that the alteration in acid-base transporters is independent of interstitial nephritis.

Conclusions: This case study demonstrates that vacuolar-type H⁺-ATPases are associated with distal renal tubular acidosis, and distal renal tubular acidosis precedes interstitial nephritis in patients with primary Sjögren's syndrome.

Keywords: H+-ATPase; Hypokalemia; Interstitial nephritis; Renal tubular acidosis; SJÖGREN’S syndrome.

Fig. 1

Histological findings of kidney biopsies. Periodic acid-Schiff (PAS) staining of the kidney obtained at initial (A) and the present hospitalization (B). Interstitial infiltration of lymphocytes was not observed at the initial time whereas it was evident in the biopsied kidney taken during the present hospitalization

Fig. 2

Patient’s clinical course. U.β2MG, urinary β2-microglobulin; KCl iv, intravenous potassium chloride

Fig. 3

Immunofluorescent staining for vacuolar type H⁺-ATPase. Immunofluorescent staining of the kidney sections obtained from the patient at first (A to D) and the second (E to H) biopsy. Kidney sections from a control subject were also showed (I to L). The vacuolar type H⁺-ATPase signals are absent in the apical membrane of the collecting duct in the present case (A, E, and I), which is indicated by positive phosphorylated aquaporin-2 signals (B, F and J). (D), (H), and (L) represent the merged images. Arrows indicate collecting duct