Nephrogenic diabetes insipidus in a 14-year-old gelding.

The research article discusses a complex case of a 14-year-old horse diagnosed with nephrogenic diabetes insipidus, a rare condition characterized by excessive thirst and urination. Despite thorough examination and testing, the cause of the horse’s urinary incontinence remains unknown.

Background of the Case

• The research revolves around a 14-year-old Cleveland Bay cross gelding horse that had been diagnosed with severe urinary incontinence (uncontrolled urination) that had persisted for a year, along with chronic polydipsia (excessive thirst) and polyuria (excessive urination) for over four years. The horse’s water intake was extraordinarily high, consuming as much as 240 liters within 24 hours.

Clinical Assessment and Findings

• Upon examination, the horse showed evident signs of urinary incontinence, polydipsia, and polyuria. Urinalysis was conducted, which showed hyposthenuria, a condition where urine is more dilute than usual. However, there was no indication of any other abnormality in the urine.
• To check for other potential health issues, the research team carried out neurological assessments, hematological and serum biochemical examinations. However, all results were within regular parameters. Further specific checks, using ultrasound and endoscopy to probe the urinary tract, also found no abnormalities.

Treatment Trial and Result

• The horse was subjected to a modified water deprivation test to see if the body could concentrate its urine. The expectation was that in a healthy horse, less water intake would make urine more concentrated. However, the horse continued to pass highly dilute urine even after five days of water deprivation.
• To further understand the horse’s condition, they administered 1-desamino-8-d-arginine vasopressin (DDAVP), a synthetic replacement for the hormone that helps regulate the body’s water balance. Again, the horse’s urine remained dilute, indicating an insensitivity to the hormone.

Conclusion

• The researchers concluded their investigations by diagnosing the horse with nephrogenic diabetes insipidus, a rare condition that causes an increase in the volume of urine and, consequently, increased thirst. The cause of urinary incontinence in this case remained elusive, although overflow incontinence — where the bladder is always so full that it continuously leaks urine — was suggested to be a possibility.
• The authors note the rarity of this condition in horses and suggest that this form of diabetes insipidus should be included in the differential diagnosis when excessive thirst and urination are observed in mature horses.