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250 Diabetes Insipidus

Diabetes Insipidus Client Education
Sheet
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may also result in reduced ADH secretion.
BASIC INFORMATION
q 2h (q 4h during the night) for 24
Animals without a discernible underlying ○ The owner should collect urine samples
Definition cause are classified as having idiopathic CDI. hours. If Uosm in one of these samples
Inadequate urine-concentrating ability due to • In NDI, the kidneys are unable to con- is > 1000 mOsm/kg (USG > 1.030),
insufficient antidiuretic hormone (ADH; i.e., centrate urine despite adequate circulating primary PD is diagnosed. If all samples
vasopressin) secretion (central diabetes insipi- levels of ADH. Frequently, the cause of have Uosm < 1000 mOsm/kg (USG <
dus [CDI]) or action (nephrogenic diabetes inadequate ADH action remains unknown 1.030), a vasopressin analog (desmopressin
insipidus [NDI]) (i.e., idiopathic NDI). NDI may also be a acetate [DDAVP]) is administered for 5
consequence of other disorders (i.e., second- days: one drop of an intranasal solution
Epidemiology ary NDI). (100 mcg/mL) is administered by the
SPECIES, AGE, SEX ○ Escherichia coli endotoxins (e.g., pyometra, owner in the conjunctival sac q 8h. During
• Affects dogs and cats pyelonephritis) and hypercalcemia may the last day of DDAVP administration,
• No breed, sex, or age predisposition interfere with the renal action of ADH. the owner should collect another series of
○ In dogs, glucocorticoids (endogenous urine samples as before. If Uosm remains
Clinical Presentation hypercortisolism or therapeutic admin- < 1000 mOsm/kg in these samples, CDI is
DISEASE FORMS/SUBTYPES istration) and mineralocorticoids (hyper- very unlikely, and the patient has primary
• CDI: hypothalamic/pituitary gland disorder aldosteronism) interfere with the renal PD or NDI instead.
• NDI: disorder at the renal level action of ADH. • Water deprivation test
• Congenital NDI and congenital CDI are ○ Used for differentiating NDI from
HISTORY, CHIEF COMPLAINT rare. primary PD (i.e., after CDI has been
• The major manifestations are polyuria (PU) excluded)
and polydipsia (PD). The PU may result in DIAGNOSIS ○ Should not be performed if azotemia or
hypovolemia. dehydration is present
• Stupor, disorientation, ataxia, and seizures Diagnostic Overview ○ The patient must be monitored throughout
possible when a large neoplasm in the area The diagnostic approach to diabetes insipidus the test.
of the pituitary is the underlying cause or is directed at ruling out metabolic, endocrine, ○ Procedure
when insufficient drinking has resulted in or other causes of PU/PD by using a CBC, ■ Fast the patient for 12 hours before
(life-threatening) hypertonic encephalopathy. routine biochemistry profile (including plasma the test.
osmolality), urinalysis, urine culture, and test(s) ■ At the start of water deprivation, empty
PHYSICAL EXAM FINDINGS for adrenal gland disorders. After other dif- the patient’s bladder, and determine
• Usually normal ferential diagnoses are excluded, differentiation the patient’s body weight, plasma
• Dehydration may be noted if the animal has of CDI from NDI or primary PD requires serial osmolality, and USG or preferably
not had free access to water. measurements of urine osmolality (Uosm), a Uosm.
• Neurologic abnormalities (e.g., stupor, trial therapy with exogenous ADH, and eventu- ■ Withhold water and monitor clinical
disorientation, ataxia) possible with ally, a water deprivation test. demeanor, body weight (after emptying
severe hypernatremia or with CDI due to bladder), and USG (or Uosm) q 2h.
hypothalamic/pituitary mass lesion Differential Diagnosis After a urine sample has been collected,
Other causes of PU/PD (pp. 812, 1271, and the bladder must be emptied.
Etiology and Pathophysiology 1442) ■ The test is stopped when 5% of body
• Normal daily water consumption < 100 mL/ weight has been lost, USG increases to
kg/d for dogs and < 250 mL/d for cats Initial Database > 1.030 or Uosm to > 1000 mOsm/kg,
• ADH is released by the neurohypophysis (i.e., • CBC: usually normal; mild hemoconcentra- USG or Uosm do not increase for >
posterior pituitary) in response to increased tion may be seen if the animal is dehydrated 6 hours, or the pet becomes clinically
plasma osmolality and, to a lesser degree, to • Serum biochemical profile: usually no dehydrated or depressed.
reduced blood volume. abnormalities except for slight hypernatremia ■ Slowly reintroduce water when the test
• ADH binds to vasopressin-2 receptors and elevated plasma osmolality in cases of is completed.
in the renal distal tubules and collecting inadequate replenishment of excreted water ○ Interpretation
ducts. Activation of these receptors results • Urinalysis: usually hyposthenuria to isosthe- ■ USG or Uosm in patients with primary
in insertion of water channels (aquaporins) nuria (urine specific gravity [USG] < 1.013, PD should slowly increase to > 1.030
in the luminal membrane of the tubular often < 1.008) but may be higher in cases or > 1000 mOsm/kg, respectively.
cells, leading to increased water absorp- of partial CDI or NDI ■ Patients with NDI will show little or
tion from the lumen of the ducts into • Other tests to rule out causes of secondary no increase in USG or Uosm.
the renal interstitium. The end result is NDI include urine culture, Leptospira serol- ○ Possible complications of the test:
concentrated urine. Water resorption also ogy, abdominal ultrasonography, and testing hypernatremia/hypertonic dehydration
depends on the osmotic gradient of the renal for hyperadrenocorticism (p. 485). (irritability, weakness, ataxia, stupor,
interstitium. coma)
• CDI results from a lack of hypothalamic Advanced or Confirmatory Testing • CT or MRI (p. 1132) of the hypothalamic/
production or release of ADH secondary • Random plasma osmolality: a large overlap pituitary area can be used to determine
to immune-mediated destruction of ADH- exists among CDI, NDI, and primary PD. whether a cranial mass is the cause of CDI.
producing neurons, cerebral trauma (head Plasma osmolality < 280 mOsm/kg suggests • Endogenous creatinine or iohexol clearance
injury), intracranial neoplasia (often a pitu- primary PD. testing or nuclear scintigraphy to estimate
itary tumor), or other hypothalamic/pituitary • Serial measurements of urine osmolality and glomerular filtration rate may be used to
lesions. In dogs, hyperadrenocorticism trial therapy with exogenous ADH rule out renal insufficiency.

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