Clinicopathological manifestations of biopsy-proven renal sarcoidosis: A retrospective cohort study

Background While many studies have reported renal involvement in sarcoidosis, there is limited description of the pathological manifestations of renal sarcoidosis. The relationship between clinical presentation, renal pathology, and prognosis remains unclear. The aim of this study is to examine the clinical, laboratory, and histological characteristics, as well as the prognosis of patients with renal sarcoidosis (RS). Methods We conducted a retrospective, single-center study of RS in renal biopsy cases treated in our department between January 2019 and December 2023. Results We identified 5 patients (4 men, 1 woman; median age 52 years, IQR 36–61 years). All patients had renal insufficiency with a median creatine level of 456 µmol/L (IQR 430.5-942.5µmol/L) and a median proteinuria of 0.5 g/24 h (IQR 0.2–0.73 g/24 h). Three (60%) of the five patients presented with both hypercalcemia and hypercalciuria. Histologically, two of the three patients who with hypercalcemia presented with renal calcinosis and tubulointerstitial nephritis (TIN) without granuloma. The other patient with hypercalcemia presented with renal calcinosis and acute tubular necrosis (ATN). The other two (40%) patients who with normal serum calcium presented with noncaseating granulomas interstitial nephritis (GTIN). For light microscopy, the interstitial inflammatory infiltrate also contains lymphocytes, monocytes cells, and sometimes eosinophils. By immunohistochemical stain, the infiltrating lymphocytes were CD4 + T cells that formed nodular granulomas, surrounded by CD8 + T cells. Chronic lesions such as interstitial fibrosis was mild in all five patients. A favorable response to steroid therapy was noted in all cases, and only one (case 4) had biopsy-proven recurrence of sarcoidosis granulomatous interstitial nephritis. Conclusions RS is extremely rare among kidney biopsy cases. Early and accurately diagnosis depends on renal pathology. The hallmark histological manifestation of RS is noncaseating GTIN, with CD4 + T cells primarily located in the center and CD8 + T cells primarily located in the periphery. Early diagnosis and prompt treatment with corticosteroids can improve the prognosis.