Vancomycin-Associated Tubular Casts and Vancomycin Nephrotoxicity

Abstract

Introduction: Vancomycin nephrotoxicity is frequent and may be due to drug-induced acute tubular necrosis (ATN) or tubulointerstitial nephritis (TIN). Vancomycin-associated tubular cast (VTC) was recently described and may represent a novel cause of vancomycin nephrotoxicity. However, much is still unknown about VTC.

Materials and methods: Thirty-seven kidney biopsy specimens from patients who were treated with vancomycin and developed acute kidney injury (AKI) were found among a total of 4673 biopsy samples between 2010 and 2019. These biopsy specimens were subjected to light microscopy, immunofluorescence, electron microscopy, and immunolocalization for vancomycin, uromodulin, myoglobin, tubular segment-specific markers, and examined for VTCs. The findings were correlated with the clinical course.

Results: VTCs displayed precipitated vancomycin casts in a background of uromodulin; the casts were limited to the distal tubules, and always associated with a background of more diffuse renal injury (ATN or TIN). The diagnosis of vancomycin nephrotoxicity was made in in 28 of 37 patients. VTC was noted in 25 of 28 biopsy samples from patients diagnosed with vancomycin nephrotoxicity and in one of nine biopsy samples from patients without this diagnosis. Vancomycin nephrotoxicity was diagnosed in 25 of 26 patients whose biopsy specimens showed VTC, but in only 3 of 11 patients without VTC in the biopsy samples.

Conclusions: VTC displays a characteristic morphologic profile amenable to ready recognition in biopsy specimens. It results from coprecipitation of vancomycin and uromodulin. It facilitates the biopsy diagnosis of vancomycin nephrotoxicity. It may have a nephrotoxic effect superimposing on and independent from the ATN or interstitial nephritis in the pathogenesis of vancomycin nephrotoxicity.

Keywords: biopsy; electron microscopy; immunostain; nephrotoxicity; vancomycin; vancomycin-associated tubular casts.

Graphical abstract

Figure 1

The background changes include acute tubulointerstitial nephritis (a), or acute tubular necrosis with a minor interstitial inflammation (b). Vancomycin-associated tubular casts (VTCs) are noted in each biopsy (hematoxylin and eosin stain; original magnification ×200 for both a and b).

Figure 2

Morphologic spectrum of vancomycin-associated tubular casts (VTCs). (a) The tubular cast is composed of variable-size granular particles. (b) It is faintly periodic acid-Schiff (PAS) positive with a “bubble” appearance. (c,d) It displays a variegated appearance. It appears in thick section as aggregated granules with focal purple glassy material consistent with uromodulin (e) and is positive for vancomycin (f). This cast is composed of polymorphous globules with focal central clearing (g). (h,i) This appearance is also noted in the thick section and vancomycin stain. (j,k) This cast is composed of vancomycin-positive solid spherical globules, associated with necrotic cells. (l) Some globules display peripheral lamellation. (Hematoxylin and eosin stain used for a, g, and j; periodic acid-Schiff stain used for b; silver stain used for c; trichrome stain used for d, toluidine blue stain used for e, h, and l; and anti-vancomycin antibody used for f,i and K. Original magnification ×400 for all panels.)

Figure 3

Morphologic spectrum of vancomycin-associated tubular casts (VTCs). This cast displays a bubble appearance with a central amorphous area (a), and is positive for vancomycin (b). This cast has an appearance suggestive of uromodulin cast (homogeneous bluish tinge by hematoxylin and eosin stain) (c); however, in thick section it displays dark granular material, representing vancomycin crystals against a background of uromodulin (d). This cast is positive for vancomycin in granular pattern (e), and positive for uromodulin in diffuse pattern (f). This cast is associated with necrotic cells (g). (Hematoxylin and eosin stain used for a, c, and g; toluidine blue stain used for d; anti-vancomycin antibody used for b and e; and anti-uromodulin antibody used for f. Original magnification ×400 for all panels.)

Figure 4

Immunolocalization of vancomycin and uromodulin. In the upper row, hematoxylin and eosin (HE) stain shows casts with necrotic cells (a). The casts are positive for vancomycin (b), but are negative for uromodulin (c). In the lower row, HE stain shows casts which have morphology of both vancomycin and uromodulin (d). The casts are positive for vancomycin (e) and uromodulin (f). (HE stain used for a and d; anti-vancomycin antibody used for b and e; and anti-uromodulin antibody used for c and f. Original magnification ×400 for all panels.)

Figure 5

Vancomycin-associated tubular casts (VTCs) in tubular segment. The cast is in a damaged tubule which is adjacent to an intact proximal tubule (a). The cast is in a damaged tubule (b) which is highlighted by kidney-specific cadherin; therefore, it is distal convoluted tubule (c). Renal cell carcinoma (RCC) is negative in the tubule which contains VTCs, but it is positive in adjacent tubules (d). In electron microscopic study, VTCs are noted in distal convoluted tubule with basolateral infolding and short villi (e). VTCs and necrotic cells are present in a damaged tubule, perhaps a collecting duct, which is adjacent to a damaged proximal tubule (f). VTCs are present in a tubule, probably thick Henle loop. (Periodic acid-Schiff stain used for a; hematoxylin and eosin stain used for b; kidney-specific cadherin for c; RCC marker used for d; and electron microscopy used for e, f, and g. Original magnification ×400 for a, b, c, and d; original magnification ×8000 for e, f, and g.)

Figure 6

Electron microscopic morphology of vancomycin-associated tubular casts (VTCs). VTCs appear as electron-dense particle clusters of variable densities, in a background of fibrillary structures typical for uromodulin (a). VTCs are composed of electron-dense aggregates with internal lamina structure (b, inset). Other components include spherules with peripheral condensation and central clearing. Transitional forms are also noted (b). VTCs appear as spherules embedded within a uromodulin background (c). (Original magnification ×28,000 for a; ×12,000 and ×28,000 (inset) for b; and ×16,000 for c.)

Figure 7

Electron microscopic morphology of vancomycin-associated tubular casts (VTCs). VTCs appear as polymorphic spherules of variable sizes, shapes, and structures, with overlapping features suggesting different phases of crystallization (a). VTCs appear as dense aggregates of spherules, enmeshing a necrotic cell (b). VTCs appear as compacted spherules associated with pale material typical for uromodulin and necrotic cells, occupying the entire tubular lumen (c). (Original magnification ×12,000 for a and c; and ×16,000 for b.)

Figure 8

Electron microscopic morphology of vancomycin-associated tubular casts (VTCs). VTCs appear as aggregated, irregularly shaped, interconnected, or single spherules with single-layered electron dense envelope (a). A single-layered electron-dense envelop with uniform granular center (b). A single-layered electron-dense envelope with a variegated center in a fibrillary background (c). A multilayered electron-dense envelope, with variegated center (d). A multilayered envelope with variable electron densities (e) which are composed of concentric laminar structures (f). Transitional forms are frequent and several forms are noted in a same biopsy or the same tubular cast. (Original magnification ×28,000 for all panels.)