In a teaching case recently published in the American Journal of Kidney Diseases, Gnemmi et al report on two unusual cases of cast nephropathy associated with light chain deposition disease in patients with Waldenström’s macroglobulinemia. The mechanisms associated with intra-tubular cast formation are incompletely understood. “Cast nephropathy” results from excessive production of monoclonal immunoglobulin chains. These casts, seen most often in the setting of multiple myeloma, have a distinctive histologic appearance. Other types of casts, with varying diagnostic specificity, are more frequently present on kidney biopsy than myeloma casts. Test your knowledge by identifying the following four types of casts.

Note: the correlation between the appearance of casts in the urine and in histology sections is not always straightforward.

1. Please identify the cast. Which of the following statements is UNTRUE?

H&E and PAS stains; original magnification, x40. Images courtesy of Dr. Isaac Stillman.

A. Diagnostic of amyloid when positive for Congo Red with apple-green birefringence under polarized light.

B. Ultrastructural examination of these casts may reveal fibrils.

C. Usually positive for IgA by immunofluorescence.

D. Nidus of formation is uromodulin.

E. Can be seen in any setting of kidney disease.

2. Please identify the cast. Which of the following statements is UNTRUE?

Trichrome stain; original magnification, x40. Image courtesy of Dr. Isaac Stillman.

A. May be present along with cellular debris or calcium oxalate crystals.

B. Positive for myoglobin by immunohistochemistry.

C. May be seen in association with cirrhosis of the liver.

D. Most prominent in the renal pyramids.

E. Associated with concentrated urine and low urine sodium.

3. Please identify the cast. Which of the following statements is UNTRUE?

H&E stain; original magnification, x40. Image courtesy of Dr. Isaac Stillman.

A. These casts may be positive for hemoglobin by immunohistochemistry.

B. May be seen in association with cirrhosis of the liver.

C. Are strongly positive for IgA by immunofluorescence.

D. Presence correlates with acute kidney injury.

E. Commonly occurs with ANCA positivity.

4. Please identify the cast. Which of the following statements is UNTRUE?

Trichrome stain; original magnification, x40. Image courtesy of Dr. Isaac Stillman.

A. Often seen with a crescentic glomerulonephritis.

B. May be present in “acute tubular necrosis”.

C. When extensive and associated with micro-abscesses, is suggestive of bacterial pyelonephritis.

D. Not seen in myeloma cast nephropathy.

E. Can be associated with eosinophilia.

Post prepared by Isaac E. Stillman, MD, Beth Israel Deaconess Medical Center, Boston, MA.

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