Chronic Kidney Disease with Sjögren's Syndrome and Hyperthyroidism: Discrepant Creatinine- and Cystatin C-Based eGFR.

We report the case of a 70-year-old woman with chronic kidney disease, hyperthyroidism, and Sjögren's syndrome who exhibited a marked discrepancy between creatinine-based and cystatin C-based estimated glomerular filtration rates(eGFRs). A kidney biopsy revealed chronic tubulointerstitial nephritis with lymphoplasmacytic infiltration, and electron microscopy showed focal subendothelial widening without electron-dense deposits. Methimazole improved the thyroid function and reduced discrepancies between eGFR estimates. Proteinuria and tubular injury markers improved after corticosteroid therapy. A correction of dehydration and an improvement in the nutritional status may also have influenced the clinical outcomes. These findings highlight the need to consider thyroid dysfunction when interpreting the renal biomarker levels.