CRP-58

CRP-58

Clinical History

The patient is a 77-year-old female with nephrotic syndrome. Negative complements and anti-double stranded DNA. BUN 35, creatine 1.5, urinary protein > 3 g/day.

Gross Description

Received in transport media are two cores measuring 5 and 7 mm in length and 1 mm in diameter. Two 1-mm pieces are taken for EM, and the remainder is bisected and equally divided for light and immunofluorescence microscopy.

Pathology

Case CRP-058 Silver

Microscopic Description, Immunofluorescence, and Electron Microscopy

Microscopic Description

Light Microscopy

The specimen consists of a fragment of renal cortex with twenty-seven glomeruli in the three levels. Four of these are obsolete. The remainder show striking lobulation and marked increase in mesangial matrix and cells. Although the nodules are somewhat similar to Kimmelstiel-Wilson nodules, there is much more hypercellularity, and the pattern of lobulation is diffuse rather than segmental. The silver stain shows numerous examples of double contours and mesangial interposition. There also appear to be a number of peripheral capillary loops with subendothelial deposits. No spike formation is identified along the epithelial surfaces. The trichrome and PASH stains show mild focal interstitial fibrosis and chronic tubular atrophy with basement membrane thickening. There are occasional inflammatory cells in the interstitium, but no tubulitis is identified. The arterioles and smaller arteries show mild intimal thickening but otherwise unremarkable.

Immunofluorescence

There are six glomeruli in these sections. These also demonstrate striking nodularity. There is segmental staining there is graded 3 for IgG and kappa light chain; 2+ for IgM and C3; trace for Clq. The staining is both mesangial and along the capillary basement membranes. However, the most intense staining is at the periphery of the large mesangial nodules. There is no glomerular staining for IgA or lambda light chain. There is no staining of the tubular basement membranes or vessels. Tubular epithelium contains numerous albumin droplets.

Electron Microscopy

Two thick sections containing a total of two glomeruli are available. These are similar and exhibit marked nodularity. Ultrastructural examination confirms the marked increase in mesangial matrix and cells. Most of the capillary lumina are obliterated. Numerous microtubular arrays are identified in the mesangium. These tubules form parallel arrays, straight or curved, although they are primarily curved. The capillary basement membranes are thickened, and numerous examples of new basement deposition are noted. Numerous large subendothelial deposits of these filaments are also identified. In contrast to the mesangial deposits, most of these are straight rather than curved. No intramembranous or subepithelial deposits are noted. No deposits are identified in the tubular basement membranes.

Diagnosis and Comments

Kidney, needle biopsy -lmmunotactoid glomerulopathy.

These findings are most consistent with immunotactoid glomerulopathy. Although some authors consider this entity to be one of the variations of fibrillary glomerulonephritis, most separate it on the basis of the larger diameter of the fibrils. This is an extremely rare lesion. It is sometimes with lymphoplasmacytic disorders, and since this biopsy demonstrates monotypical kappa light chain staining, I think a lymphoplasmacytic neoplasm should be ruled out. The immunofluorescence and electron microscopic findings do not support a diagnosis of light chain nephropathy or cryoglobulinemia.

Blood urea nitrogen (BUN) is used as a measure of the glomerular filtration rate and is increased in renal failure.