Wednesday, January 5, 2011

What's the Differential Diagnosis of Polydipsia and Polyuria in Dogs and Cats?

There are many potential causes of polyuria and polydipsia.  Primary disorders of water balance (i.e. central diabetes insipidus, primary nephrogenic diabetes insipidus and primary polydipsia) although uncommon, should always be considered in the differential diagnosis of polyuria and polydipsia. In general, animals with these disorders have only one laboratory abnormality; a low urine specific gravity (SG) or osmolality.

In most instances the more common causes of polyuria and polydipsia (e.g. hyperadrenocorticism, chronic renal failure, pyelonephritis and pyometra) have other specific and obvious abnormalities on screening laboratory tests (complete blood cell count, serum biochemical profile and urinalysis). In some cases, however, a low urine SG is the only abnormality found in animals with these latter disorders.

The work-up for polyuria and polydipsia can be tedious, time-consuming, expensive, confusing and not without significant patient morbidity, especially in those dogs and cats with normal or near-normal screening test results. This chapter focuses on the diagnostic approach, especially the problems associated with testing, and the treatment of dogs and cats with disorders of water balance.

Differential diagnosis
The causes of polyuria and polydipsia can be divided into those that cause primary polydipsia (with secondary polyuria) and those that cause primary polyuria (with compensatory polydipsia). These are listed in the table below.

The major cause of primary polydipsia in dogs is psychogenic polydipsia. In contrast, the causes of primary polyuria are much more numerous and can be subdivided into the categories of: central diabetes insipidus; primary nephrogenic diabetes insipidus; secondary nephrogenic diabetes insipidus; and osmotic diuresis.


1. Primary polydipsia

  • Psychogenic polydipsia (compulsive water drinking)
  • Dipsogenic diabetes insipidus (thirst centre abnormality)
  • Metabolic disorders (e.g. hyperthyroidism, hepatic failure)

2. Primary polyuria

Central diabetes insipidus (neurogenic, cranial, ADH-responsive)

  • Idiopathic
  • Trauma-induced
  • Neoplastic
  • Post-hypophysectomy

Primary nephrogenic diabetes insipidus (congenital or familial)

Secondary nephrogenic diabetes insipidus (acquired)

  • Acromegaly
  • Chronic renal disease
  • Drug administration
  • Liver disease
  • Hyperadrenocorticism
  • Hypercalcaemia
  • Hyperthyroidism
  • Hypoadrenocorticism
  • Hypokalaemia
  • Leptospirosis
  • Postobstructive diuresis
  • Pyelonephritis
  • Pyometra

Osmotic diuresis (increased renal tubular solute load)
  • Diabetes mellitus
  • Primary renal glycosuria (e.g. Fanconi’s syndrome)
  • Postobstructive diuresis
  • Renal failure
  • Leptospirosis

In our next blog post, I will talk about my approach to working up the dog or cat with polyuria or polydipsia.


jyotsna said...

Thank you Sir,
you have given very detailed causes of polydipsia and polyuria in dogs .It would be great if you please highlight on the treatment part of that as well.

Dr. Mark E. Peterson said...

See these posts:

Since there are so many causes of polyruria, it would be impossible to discuss treatment of all of the causes in 1 blog post.

EJ said...

In an Eleven y/o female black Lab, that has been healthy, except for an eyelid neoplasm, removed 1 yr ago. She has had 20lbs wt gain over the past 2 yrs since being rescued, and has a couple subcutaneous palpable nodules. What is the likely DDX, and most prudent recommendation regarding workup, i.e., what should I do on a limited budget, in this older dog, at this point? What should I watch for that would be a worrisome or diagnostically important change or finding? Thank You , Edward J, MD

Dr. Mark E. Peterson said...

If I had the solution to why dogs (and people) gained weight, I'd be famous! Most diseases that cause weight gain will lead to other signs, including an increase in thirst and urination or hair loss.

In any 11-year old dog, screening with a complete blood count, serum chemistry panel, and urinalysis is a must, even without the weight gain. That would be the first step in determining if anything else is wrong.

Is her activity level decreased? If so, your vet should certainly check for arthritis, which is also common in older dogs.

Dr. Mark E. Peterson said...

Yes see your vet.