CRP-47

CRP-47

Clinical History

The patient is a 63 year old woman. History of E. coli sepsis with positive blood and urine cultures. BUN 124, creatinine 4.4. Treated initially with gentamicin, but subsequently switched to different antibiotics.

Gross Description

Received in Zeus fixative are three cores measuring 6, 8 and 12 mm in length and 1 mm in diameter. A 1-mm piece is taken for EM, and the remainder is submitted for immunofluorescence. Received in Carson's fixative is one core measuring 8 mm in length and 1 mm in diameter. A 1-mm piece is taken for EM, and the remaining tissue is submitted for light microscopy.

Pathology

Case CRP-047 PASH

Microscopic Description, Immunofluorescence, and Electron Microscopy

Microscopic Description

Light Microscopy

The specimen consists of a single fragment of renal cortex that contains fifteen glomeruli in the three levels. All of these are normal except for mild mesangial expansion. There is no segmental proliferation or necrosis, and no crescents are present. The capillary basement membranes are unremarkable with the silver and PASH stains. There is mild interstitial fibrosis with mild focal tubular atrophy. However, there is severe interstitial edema, and the interstitium is expanded by numerous white blood cells. This is primarily a mixture of lymphocytes and polymorphonuclear leukocytes, although there are also occasional plasma cells and a few eosinophils. Numerous examples of tubulitis are identified. Many of the tubules contain white blood cell casts. A number of arterioles are present in the biopsy. These show mild intimal thickening, but they are otherwise unremarkable. A gram stain on this tissue is negative with an adequate control.

Immunofluorescence

There are six glomeruli in the sections. All of these show normal morphology. There is 1+ diffuse granular C3 staining in the mesangium. Stains for IgG, IgM, IgA, Clq and light chains are negative in the glomeruli. There is no staining of the vessels or tubular basement membranes.

Electron Microscopy

Two thick sections containing a total of three glomeruli are available. These are similar to those described above and show essentially normal morphology. Ultrastructural examination reveals mild increase in mesangial matrix. The capillary basement membranes show no significant thickening, and the epithelial cell foot processes are generally well preserved, although there is focal fusion. No deposits are identified in the glomeruli. Many of the tubules show focal epithelial cell degeneration and necrosis. Occasional myelin figures are noted in the proximal tubular epithelium.

Diagnosis and Comments

Kidney, needle biopsy - Acute pyelonephritis.

These findings are most consistent with acute pyelonephritis. However, the history of gentamicin administration complicates the interpretation somewhat. Gentamicin toxicity .generally causes acute tubular necrosis similar to that caused by ischemia, and there is usually no significant interstitial inflammation associated with gentamicin toxicity. Therefore, the typical changes associated with gentamicin toxicity could easily be masked by the presence of acute pyelonephritis. The finding of myelin bodies in the proximal tubular epithelium is interesting. These structures are not specific for gentamicin administration, but they are considered to be markers of gentamicin and other aminoglycosides. However, their presence does not necessarily indicate clinical toxicity. In summary, although there may be a component of gentamicin toxicity, I think that all of the tubulointerstitial changes in this biopsy can be ascribed to acute pyelonephritis.

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