Uremic Encephalopathy in Horses

Abstract

Background: Uremic encephalopathy refers to neurological manifestations resulting from renal failure. There are reports of this condition in several animal species. Regardless of the species, it may occur in association with acute or chronic cases of renal failure. There are almost no reports or studies in the literature on horses. Specific publications are limited to individual reports and a survey of 5 cases over a 20-year period, in addition to citations in books and reviews on renal alterations in this species. The objective of this study is to report 6 cases of uremic encephalopathy in horses, relating the manifestations to the underlying condition, laboratory results and outcome of the case.
Cases: Six cases of uremic encephalopathy were identified, representing 0.1% of the total number of equine cases treated between 2008 and 2023 (6,200) at the Veterinary Hospital of FMVZ-USP, of different breeds and ages, related to both acute and chronic cases of renal failure, with a predominance of acute cases. The clinical manifestations, primary conditions, laboratory values of urea and creatinine close to neurological manifestations, and case outcome are described. Regarding the underlying causes, in our cases, we found an association with acute renal failure during the course of colic syndrome in 3 animals (1 due to excess non-steroidal anti-inflammatory drug for 14 days), 1 related to a case of rhabdomyolysis and 1 with chronic renal failure. In the others and also in the previous ones, several factors contributed to the renal injury, such as excessive use of non-steroidal anti-inflammatory drugs and/or in combination with dehydration. The 6 cases presented the same set of manifestations reported for humans and animals, with a predominance of mental state alterations, which appeared in 5 of the 6 horses. Treatment was based mainly on fluid therapy, correction of electrolyte imbalances and use of anticonvulsants when necessary. Five cases died and 1 was discharged from hospital, unrelated to the degree of azotemia, but with milder manifestations. Excluding the animal that was discharged from hospital, histopathology of the brain was performed in only 2 of the 5 animals that died, with findings compatible with those of other species, but without the findings in astrocytes reported for other cases in horses.

Discussion: The cases presented a pattern similar to that described in the literature for horses and other species, both in relation to the findings and the historical information. Our cases presented variation in urea and creatinine values, but all were quite high and without significant improvement with fluid therapy, indicating the presence of intrinsic renal injury. It is important to remember that in addition to the initial condition and the possibility of previous renal disease without manifestations, the abusive use of medications that are harmful to the kidney and failure to deal with dehydration may contribute to the occurrence of renal injury or worsening of preexisting conditions, and may favor the occurrence of neu-
rological manifestations associated with renal failure. It is concluded that uremic encephalopathy in horses is rare, with no predisposition to breed, sex or age, and may be associated with acute and chronic cases of renal failure of various origins, with no direct relation to the severity of azotemia, with a poor prognosis. Therefore, it is necessary for veterinarians to be aware of the possibility of this condition for prompt diagnosis and differentiation with other situations that can cause similar manifestations and concomitant with renal failure.
Keywords: azotemia, fluid therapy, kidney disease, renal, uremia.