a) Central diabetes insipidus (CDI)
b) Nephrogenic diabetes insipidus (NDI) - which can be i) Primary (familial) or ii) Secondary (acquired)
Both result in the kidneys being unable to retain water, resulting in excessive losses of dilute urine (polyuria) and a compensatory increase in thirst (polydipsia)
a) CDI- caused by damage (eg trauma, tumours or congenital deformities) to the neurohypophyseal system, resulting in insufficient secretion of the hormone arginine vasopressin (AVP) from the suproptic and paraventricular nuclei in the hypothalamus of the brain. AVP is important in the regulation of water loss as urine and without it the animal is unable to concentrate it's urine.
b) NDI- caused by insensitivity of AVP receptors in the kidney to the presence of AVP and so the animal is unable to concentrate it's urine.
a) Centraldiabetes insipidus (CDI) can occur at any age and in any breed or sex. Onset can be any age - in dogs from 7 weeks to 14 years, in cats 8 weeks to 6 years. In one report it was suggested that it might be an inherited disorder in 2 Afghan puppies, and an affected litter has also been reported in German Shorthaired Pointers.
b) Nephrogenicdiabetes insipidus (NDI) Primary congenital NDI has been reported to occur in Huskies in which AVP receptors are present in the kidney nephrons but they do not respond properly to AVP. The most common form of DI is secondary NDI due to renal or metabolic disorders. Primary NDI has only been identified in puppies and kittens under 18 months of age.
The main clinical signs are increased thirst (polydipsia) and increased urination (polyuria) which may appear as incontinence to some owners.
Other signs may be present if the animal has secondary diabetes insipidus, for example neurological signs may be present if the animal has a brain tumour.
a) CDI:Plasma AVP concentrations are low or absent. Urine specific gravity remains very low (hyposthenuric) 1.005 or less. maximum 1.015-1.020 even when severely dehydrated.
b) NDI:. Plasma AVP concentrations are normal or high.
Diagnosis is made by a modified water deprivation test (NB Water deprivation tests are potentially dangerous because severe dehydration and ischaemic renal damage can occur and so they should only be performed when the animal is kept under direct observation):
Administration of 3-5 Units ADH intramuscularly to the animal with an empty bladder should stimulate the renal receptors in cases of CDI, and so induce the animal to produce more concentrated urine (specific gravity increased by 50% or more) within 2-3 hours. Alternative administration routes include oral (0.05 - 0.2 mg desmopressin every 8 hours, or 1-4 drops of nasal spray into the conjunctival sac every 12 hours for 5-7 days. ADH would have minimal effect in patients with RDI.
Hyperadrenocorticism can mimic CDI because there is a suppression of AVP secretion, and these patients may respond positively to ADH administration, so this diagnosis must be ruled out before the above tests are conducted.
CDI : The synthetic analog of AVP (desmopressin acetate) is the most commonly used form of treatment. 1-4 drops of the nasal spray are instilled into the conjunctival sac twice daily. It has been used orally in dogs, but it is less reliable, and the starting dose is 0.1mg 3x daily reducing to 0.1-0.2mg twice daily. By injection the dose is 0.5-2 mg subcutaneously 1-2x daily. Lypressin is an alternative but it has a shorter duration of action.
a) CDI :. Trauma such as head trauma can result in transient diabetes insipidus which may last 1-3 weeks. In other cases it may be permanent unless treated. When treated appropriately the clinical signs can disappear - often within 2 weeks. Animals with brain tumours have a poor prognosis
b) NDI :. Animals with primary NDI have a guarded prognosis, however in those with secondary NDI the condition may be reversible if the underlying cause can be treated
If treatment is not successful continuous access to water must be available, and animals can live an acceptable life.
Long term problems
For animals that are not stabilised a continuous supply of water has to be made available, and owners have to be able to put up with large volumes of urine being passed
Updated January 2016
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