Central Diabetes Insipidus

33 Central Diabetes Insipidus



David L. Panciera



1. What are the causes of central diabetes insipidus?

Central diabetes insipidus is a deficiency of antidiuretic hormone (ADH) secretion by the pars intermedia of the pituitary gland or a deficiency of ADH production by the hypothalamus. The reported causes of deficiency in dogs include neoplasia, trauma, and congenital abnormalities.


2. What clinical signs are caused by diabetes insipidus?

The primary and only clinical signs of diabetes insipidus in most cases are polyuria and polydipsia (PU/PD), which typically are severe. Urinary incontinence is another common complaint and is the result of the marked polyuria induced by diabetes insipidus. Dogs with neoplasia or trauma may have clinical signs related to damage of surrounding structures in the brain. Progression of neurologic abnormalities often occurs in dogs with pituitary neoplasia.


3. How is a diagnosis of diabetes insipidus established?

It is important to thoroughly evaluate a dog with suspected diabetes insipidus for other diseases that could cause PU/PD. Persistent isosthenuria or hyposthenuria confirms the presence of polyuria, while finding a urine specific gravity above 1.030 rules out persistent PU/PD. Hyposthenuria is most frequently found in dogs with central or nephrogenic diabetes insipidus, primary polydipsia, and hyperadrenocorticism. With the possible exception of evidence of dehydration, the complete blood count (CBC) and serum chemistry values of dogs with diabetes insipidus should be normal.


A water deprivation test may be performed for confirmation of the diagnosis.


4. What is the protocol for performing a water deprivation test?

For the results of a water deprivation test to be valid, causes of PU/PD other than central diabetes insipidus, nephrogenic diabetes insipidus, and primary (psychogenic) polydipsia should already have been eliminated. The water deprivation test is contraindicated if the animal is dehydrated, azotemic, or hypercalcemic.


Water can be gradually restricted for 3 days before the water deprivation test to reestablish the renal medullary concentration gradient.


After the dog has fasted for 12 hours, the urinary bladder is emptied by catheterization and urine specific gravity, body weight, and blood urea nitrogen (BUN) are measured. Water continues to be withheld and the above measurements are repeated every 1 to 2 hours until one of the following occurs: urine specific gravity becomes greater than 1.030; weight decreases by 5% or more; azotemia develops; or the dog shows signs of depression, disorientation, or vomiting. The water deprivation test must be terminated if the animal loses more than 5% of its body weight, develops azotemia, or becomes ill; failure to terminate the test when these signs occur may result in life-threatening dehydration and circulatory collapse. Dogs with diabetes insipidus may become dehydrated rapidly.


After completion of the water deprivation test, the dog should be given desmopressin (DDAVP) (5 μg for dogs <15 kg and 10 μg for dogs >15 kg) intravenously (IV) or subcutaneously (SQ). The urine specific gravity should be measured 30, 60, 90, and 120 minutes after DDAVP administration or until the urine specific gravity is above 1.030. At the end of the test, do not allow the dog to drink a large amount of water immediately, because this could result in water intoxication and cerebral edema.


The dog with complete diabetes insipidus will have minimal increase in urine specific gravity (≤1.012) after 5% dehydration. Dogs with partial diabetes insipidus may have a urine specific gravity up to 1.018, but rarely higher. Following administration of DDAVP after 5% dehydration on the water deprivation test, the urine specific gravity typically increases to between 1.018 and 1.030. Renal medullary washout usually prevents further urine concentration.

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Jul 31, 2016 | Posted by in INTERNAL MEDICINE | Comments Off on Central Diabetes Insipidus

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