Equis ISSN 2398-2977

Polydipsia / polyuria

Contributor(s): Rachael Conwell, Graham Munroe, Prof Jonathon Naylor, Carla Sommardahl, Han van der Kolk

Introduction

  • Polydipsia (increased thirst, considered >100 ml/kg BW/day in adult horses) and polyuria (increased urine production, considered >50 ml/kg BW/day in adult horses). Foals have greater urine output for body size due to milk diet and low renal solute load; urine production of up to 148 ml/kg BW/day is considered normal.
  • Cause: there are many different potential causes. Primary polydipsia with secondary polyuria is mainly due to hot environmental conditions, psychogenic disorders or thirst disorders; polyuria with secondary polydipsia includes conditions caused by solute diuresis, water diuresis and iatrogenic interventions.
  • Signs: vary with each individual disease entity.
  • Diagnosis: careful history taking to determine the amount of urine production and water consumption, measurement of urine production/water consumption is essential, urinalysis, measurement of renal function, water deprivation test.
  • Treatment: depends on the individual disease entity.
  • Prognosis: depends on the individual disease entity.

Pathogenesis

Etiology

Primary polydipsia
  • Excessive water intake which secondarily   →   a water diuresis and polyuria.
  • Environmental conditions, ie hot, humid climates, eg southern USA; physiological demands, such as lactation.
  • Apparent psychogenic polydipsia due to boredom in stabled horses (can be extreme).
  • Primary disorders of thirst which are poorly understood.

Polyuria with secondary polydipsia

  • Solute diuresis:
  • Water diuresis:
    • Decreased water resorption in the collecting tubules of the kidney or inappropriately large voluntary water intake   →   urine osmolality less than plasma osmolality.
    • Insufficient antidiuretic hormone, ADH (also called Arginine Vasopressin (AVP)), neurogenic (central) diabetes insipidus, PPID   Pituitary: adenoma  , encephalitis, pituitary abscess, pituitary neoplasia, aberrant parasite migration, head trauma   CNS: brain trauma  .
  • Insensitivity of receptors of distal collecting duct and collecting tubules in kidney to ADH:
  • Renal medullary wash-out (loss of medullary Na, Cl and urea):
    • Chronic diuresis of any cause.
    • Inappropriate renal tubular sodium handling.
    • Apparent psychogenic polydipsia.
  • Iatrogenic:

Predisposing factors

General
  • Varies according to each different disease process.

Specific

  • Varies according to each specific disease.

Pathophysiology

  • Conservation of body water relies upon:
    • Production and release of ADH in response to appropriate stimulation.
    • Sensitivity of nephrons to ADH.
    • Minimum of 1/3 functioning nephrons.
    • Hypertonic renal medullary interstitium.
  • Polyuria/polydipsia occurs when one or more of these steps is not functioning.
  • Polydipsia - increased thirst.
  • Polyuria - increased urine production.
  • Primary polydipsia   →   secondary polyuria can be caused by hot environmental conditions, apparent psychogenic disorders or poorly understood disorders of thirst.
  • Polyuria   →   secondary polydipsia is more common and includes conditions caused by solute diuresis, water diuresis and iatrogenic interventions.

Timecourse

  • Varies according to disease process.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Moses M E et al (2013) Antidiuretic response of a horse affected with pituitary pars intermedia dysfunction to desmopressin acetate. Equine Vet Educ 25 (3), 111-115 VetMedResource.
  • Schott H C (2011) Water homeostasis and diabetes insipidus in horses. Vet Clin North Am Equine Pract 27 (1), 175-195 PubMed.
  • Durham A E et al (2009) Type 2 diabetes mellitus with pancreatic ² cell dysfunction in 3 horses. Equine Vet J 41 (9), 924-929 PubMed.
  • McKenzie E C (2007) Polyuria and polydipsia in horses. Vet Clin North Am Equine Pract 23 (3), 641-653 PubMed.
  • Schott H C (2007) Chronic renal failure in horses. Vet Clin N Am Equine Pract 23 (3), 593-612 PubMed.
  • Brashier M (2006) Polydipsia and polyuria in a weanling colt caused by nephrogenic diabetes insipidus. Vet Clin N Am Equine Pract 22 (1), 219-227 PubMed.
  • Abutarbush S M (2005) Diagnosis of urinary tract disease in the horse. Large Anim Vet Rounds (2), 1-6 VetMedResource.

Other sources of information

  • Kohn C W & Hansen B (1998) Polyuria and Polydipsia. In: Equine Internal Medicine. Eds: Reed S M & Bayley W M. W B Saunders & Co, USA..
  • Roussel A J & Carter G K (1989) Polyuria and Polydipsia. In: Problems in Equine Medicine. Ed: Brown C M. Lea & Febiger, USA. pp 150-160.


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