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Sjögren's syndrome (SS) is an autoimmune disease that affects exocrine glands, manifesting with keratoconjunctivitis and xerostomia. Kidney involvement can also be present in up to 33% of patients as renal tubular acidosis, nephrocalcinosis, and electrolyte disturbances. Being tubulointerstitial nephritis the most common histopathological finding in kidney biopsy.
A 29-years Guatemalan female with no past medical history, consulted to the emergency room with 2-years history of generalized weakness and weight loss. During interrogation the patient disclosed polyuria, polydipsia, xerophthalmia and xerostomia. Laboratory examination revealed glucose >800 mg/dl, potassium 3.8 mEq/L, sodium 131 mEq/L. calcium 8.5 mEq/L, phosphorus 1.6 mg/dl, chloride 101 mOsm/lt and magnesium in 2.46 mg/dl. Urine showed hematuria (10 cells/hpf), and renal blood tests had a creatinine value of 1.68mg/dl, (eGFR 42 ml/min/1.73m2 by MDR/CKR-EPI) associated with proteinuria 290 mg/day and urinary anion gap 4.8. Venous blood gas analysis reported metabolic acidosis with normal anion gap (15). With the suspicion of an autoimmune disease, we ran a Schirmmer test, Anti-Ro, Anti-La antibodies and C3-C4, being all positive except for C3-C4. Bilateral Renal USG reported normal size kidneys with bilateral medullary nephrocalcinosis. Considering AKI, proteinuria, and hematuria a kidney biopsy was performed and reported: 28 glomeruli, 9 with global sclerosis, mesangial expansion, lymphoplasmacytic infiltrate in the tubule-interstitium associated with tubular atrophy in 15-20%, with no endocapillary or extra capillary hypercellularity. Medulla with amorphous intratubular calcium deposits and negative immunofluorescence for IgG, IgA, IgM, C1q, Kappa, Lambda. It was determined the patient debuted with tubular acidosis secondary to Sjogren’s Syndrome. The patient was medicated with prednisone (1mg/kg/day), azathioprine 50 mg qday, and sodium bicarbonate 1gr TID. One week later, microproteinuria showed a 20% decrease (232 mg/day), metabolic acidosis ameliorated, and symptoms improved significantly. One month later the metabolic acidosis continued (HCO3std 14mmol/l), the patient was titrated up of oral sodium bicarbonate dose with improvement.
Kidney involvement in Sjögren's syndrome occurs in 33% of cases as renal tubular acidosis. electrolyte abnormalities, AKI, nephrocalcinosis and tubulointerstitial nephritis as the main histopathological finding. 1-2 The finding of nephrocalcinosis and acute kidney injury is associated with poor prognosis. Treatment for kidney manifestations of SS consists in immunosuppressants for control of the underlying autoimmune disease but further investigation is needed to understand the best treatment.