Cholesterol crystals tubulointerstitial injury during nephrotic syndrome; can be classified as tubular crystallopathy?

Introduction: Cholesterol crystals and granulomas in tubular lumen and interstitium of the kidney are infrequent findings during nephrotic syndrome (NS) and are poorly described. We attempt to discuss cholesterol crystals in NS as a form of crystallopathy. Case Presentation: Three cases of 207 (1.5%) performed kidney biopsies, between 2001 and 2019, in patients with NS, showed cholesterol crystals deposition in tubules, interstitium and even cholesterol granulomas with some degree of interstitial mononuclear inflammation with giant cells, interstitial fibrosis and variable tubular atrophy. Oil Red O staining revealed lipid laden macrophages in interstitium and lipid droplets in tubular epithelium. Two patients had membranous glomerulonephritis (MGN) and one membranoproliferative glomerulonephritis (MPGN). The proteinuria ranged from 6.08 to 12.57 g/24 hours, lasting from 1 to 22 months. All had hypertension, high values of serum cholesterol and triglycerides. Conclusion: Clinically significant deposition of cholesterol crystals in kidney is mainly in atheroembolic renal disease, however deposition of cholesterol crystals during NS is rare and it is not considered a form of crystallopathy. Cholesterol crystals do not seem to be correlated with degree of proteinuria, persistence of NS or type of glomerulonephritis, but it is correlated with amount of serum cholesterol which is strongly associated with the severity of NS. Therefore we propose it as tubular crystallopathy, in the setting of NS associated hypercholesterolemia which may cause chronic kidney disease (CKD).