Renal medullary crest necrosis associated with phenylbutazone therapy in horses

Area of Science:

• Veterinary Pathology
• Equine Medicine
• Toxicology

Background:

• Analgesic nephropathy, characterized by renal papillary necrosis, is well-documented in humans and rats.
• Phenylbutazone is widely used for pain management in horses, often at maintenance dosages.
• Equine renal pathology can present unique morphological features distinct from other species.

Purpose of the Study:

• To report and characterize renal medullary crest necrosis in horses receiving phenylbutazone.
• To compare the equine condition with human and rat analgesic nephropathy.
• To propose appropriate terminology for this specific equine renal lesion.

Main Methods:

• Histopathological examination of 35 equine cases with renal lesions.
• Morphological comparison with documented cases of renal papillary necrosis.
• Etiological investigation considering drug dosage and potential contributing factors.

Main Results:

• Thirty-five horses exhibited renal medullary crest necrosis, morphologically similar to analgesic nephropathy.
• The primary lesion was focal medullary necrosis with sequestration of renal crest fragments.
• Secondary cortical lesions included tubular dilatation, filtrate retention, and interstitial edema, suggesting ischemia as a contributing factor.

Conclusions:

• Renal medullary crest necrosis is a distinct pathological entity in horses associated with phenylbutazone administration.
• The term 'renal medullary crest necrosis' is proposed as more accurate for this equine condition than 'renal papillary necrosis'.
• Ischemia in conjunction with phenylbutazone is the suggested etiology for this equine kidney lesion.