Pigmentation of renal cortical tubules in horses.

The research study examines an uncommon case of pigmentation in the renal cortical tubules of a horse, which appeared similar to pigmentary nephrosis found frequently in cattle and goats but was distinctive in composition and causes.

Case Overview

• An adult male horse demonstrated a rare form of pigmentation in the kidney cortex, which did not resemble any recorded antecedents.
• Postmortem and histological examination revealed granular brown pigmentation and abnormal thickening in the epithelium of the convoluted part of the proximal tubules.

Microscope Analysis

• Under optical and electron microscope, not only were pigmented tubular cells visible but also the surrounding thickened basement membrane.
• The membrane, when left unstained, appeared brown which is an unusual observation.

Histochemical Identification

• Using histochemical methods, it was determined that the pigmentation didn’t contain melanin.
• The thickened membrane was determined to contain lipofuscin, a kind of pigment.
• The granules within the epithelium contained lipofuscin which also included iron (liposiderin).

Electron Microscopy Observation

• On viewing the thickened and pigmented membrane under electron microscopy, it exhibited a moderately thickened basement membrane from the inside and a stratum of irregular thickness from the outside.
• The external layer appeared to be composed of moderately electron-dense granules seeming to contain residues of degenerating cytoplasmic structures, possibly originating from fibroblasts.
• The ultrastructure of the granules showed no resemblance to melanin or hemosiderin but were similar to the granules observed in the residual bodies of cells which is akin to lipofuscin.

Conclusion

• The peculiar pigmentation of the basement membrane bears a close resemblance to that of the “cloisonne kidney” found in goats.
• However, the absence of ferritin in the basement membrane rules out the pathogenic explanation typically given in those cases, which involves pigment deposition on basement membranes due to tubular hemosiderosis after hemolysis.
• The study concludes that the changes in tubular epithelial cells and basement membrane along with the distinctive pigmentation of the kidney points towards findings characteristic of lipofuscinosis.