Nephrogenic diabetes insipidus in a 14-year-old gelding

Polyuria and Polydipsia in Horses

Polyuria and polydipsia are rare, but significant, manifestations of several different diseases of horses. Causes can be endocrine, iatrogenic, psychogenic, infectious, or toxic in nature and can also be due to primary renal disease or diseases of other organs, such as the liver. Although numerous causes of polyuria and polydipsia in horses exist, the most common conditions include chronic kidney disease, pituitary pars intermedia dysfunction, and psychogenic polydipsia with secondary polyuria. Additional testing is dictated by history, other clinical signs, and the results of blood work and/or urinalysis. Prognosis for horses with polyuria and/or polydipsia varies significantly based on the underlying cause.

Urinary Incontinence and Urinary Tract Infections

Urinary incontinence results from disorders of the lower urinary tract or neurologic diseases either of the nerve supply to the bladder/urethra or within the central nervous system. Congenital causes include patent urachus and ectopic ureter. Coordination of lower urinary tract function involves the interaction of both the sympathetic and parasympathetic system as well as somatic branches of the central nervous system. Well-recognized causes of incontinence include equine herpes virus 1 myeloencephalopathy, polyneuritis equi (neuritis of the cauda equina), and sacral/coccygeal trauma. Idiopathic bladder paralysis is characterized by bladder paralysis and sabulous cystitis in the absence of overt neurologic deficits.

Therapeutics for Equine Endocrine Disorders

Equine endocrine disease is commonly encountered by equine practitioners. Pituitary pars intermedia dysfunction (PPID) and equine metabolic syndrome (EMS) predominate. The most logical therapeutic approach in PPID uses dopamine agonists; pergolide mesylate is the most common. Bromocryptine and cabergoline are alternative drugs with similar actions. Drugs from other classes have a poor evidence basis, although cyproheptadine and trilostane might be considered. EMS requires management changes as the primary approach; reasonable justification for use of drugs such as levothyroxine and metformin may apply. Therapeutic options exist in rare cases of diabetes mellitus, diabetes insipidus, hyperthyroidism, and critical illness-related corticosteroid insufficiency.