Endocrine disorders - Pituitary Gland: Diabetes Insipidus

Diabetes Insipidus

• Total or relative lack of ADH (anti-diuretic hormone)

• Failure to concentrate urine → excessive thirst

• If the animal cannot drink or access water is restricted they will rapidly become dehydrated

ADH

Allows the insertion of aqueous channels into the collecting ducks and thereof the reabsorption of water

Without ADH

Water remains in the filtrate (urine) and is lost → dilute urine → loss of water → thirst → polydipsia

Central diabetes insipidus

Insufficient production and release of ADH by the pituitary

Nephrogenic diabetes insipidus

Inability of the renal tubules to respond to ADH

Clinical signs of Diabetes Insipidus

• Polyuria

• Polydipsia

• Urinary incontinence

• Urinating during the night

• +/- Neurological signs

Diagnosis of Diabetes Insipidus

• Clinical signs

• Urine specific gravity less than 1.008 - really dilute

• Rule out other causes of PUPD - cushings, diabetes melitus, hyperthyroidism

• Water deprivation test

• Trial treatment with DDAVP (desmopressin) - cascade (replaces the action of ADH)

Water Deprivation Test

• Water is gradually reduced for 3 days prior to test - reduces risk of medullary washout (should still remain hydrated)

• STOP is the patient becomes dull, lethargic, azotaemic or hypernatraemic

• Normal SG = DI is unlikely

• SG <1.020 = DI suspected

Water Deprivation Test - Process

1. Weight the patient, empty balder and measure baseline SG

2. Place in a kennel with without food and water

3. Monitor body weight and urine SG every hour

4. Continue until patient has lost 5% of bodyweight (due to loss of water) or SG >1.025

Water Deprivation Test - Central Diabetes Insipidus vs Nephrogenic Diabetes Insipidus

Once rehydrated, repeat water deprivation test, but challenge with desmopressin (DDAVP) - Analogue of ADH - same action as ADH

• Increase in SG = Central DI - Kidneys respond, but ADH is not being produced

• Minimal/no change in SG - Nephrogenic DI - Kidneys aren’t responding to the ADH

Treatment of Central DI

Remove underlying cause

Desmopressin DDAVP

• Injectable

• Oral

• Intranasal

• Subconjunctival sac - eyedrop, absorbed well over the mucous membrane

Treatment of Nephrogenic DI

• Treat underlying cause

• Diet and other supportive meds available

Desmopressin

Hormone analogue - replaced action of endogenous ADH

Desmopressin - pharmacology

• Used via the cascade so no licensed version for pk/pd studies in dogs

• In people bioavailability varies by route and other features (half life) will be impacted by renal function

Nursing considerations for Diabetes Insipidus

• Continuously access to water (except during water deprivation or ADH tests!)

• Measure water intake on a daily basis

• Allow patient the opportunity to frequently urinate

• Owner support

Nursing considerations for Diabetes Insipidus - Owner support

• Good prognosis (depending on underlying cause)

• Importance of access to water

• Treatment is lifelong

• Regular vet checks