Definition

Diabetes insipidus (DI) is a disorder of water metabolism characterized by polyuria, urine of low specific gravity or osmolality (so-called insipid, or tasteless, urine), and polydipsia.

Pathophysiology

• Central DI-deficiency in the secretion of ADH
• Nephrogenic DI-renal insensitivity to ADH

Systems Affected

• Endocrine/Metabolic
• Renal/Urologic

Genetics

N/A

Incidence/Prevalence

• Central DI-rare
• Nephrogenic-rare

Geographic Distribution

N/A

Signalment

Signs

• Polyuria
• Polydipsia
• Incontinence-occasional

Causes

Risk Factors

N/A

Differential Diagnosis

CBC/Biochemistry/Urinalysis

• Usually normal, hypernatremia in some patients
• Urinary specific gravity low (usually <1.012, often <1.008)

Other Laboratory Tests

Plasma ADH

Imaging

MRI or CT scan if a pituitary tumor is suspected

Diagnostic Procedures

• Modified water deprivation test (see Appendix II-A for protocol)
• ADH supplementation trial-therapeutic trial with synthetic ADH (DDAVP); a positive response (water intake decreases by 50% in 3–5 days)
• Rule out all other causes of PU/PD before conducting an ADH trial.

Pathologic Findings

Degeneration and death of neurosecretory neurons in the neurohypophysis (CDI)

Appropriate Health Care

Patients should be hospitalized for the modified water deprivation test; the ADH trial is often performed as an outpatient procedure.

Activity

Not restricted

Diet

Normal, with free access to water

Client Education

• Review dosage of DDAVP and administration technique
• Importance of having water available at all times

Surgical Considerations

N/A

Drug(s) Of Choice

• CDI-DDAVP (1–2 drops of the intranasal preparation in the conjunctival sac q12–24h to control PU/PD); alternatively, the intranasal preparation may be given SC (2–5 µg q12–24h). An oral preparation of DDAVP is available in 0.1–0.2 mg tablets with each 0.1 mg comparable to 1 large drop of the intranasal preparation
• NDI-hydrochlorothiazide (2–4 mg/kg PO q12h)

Contraindications

None

Precautions

Overdose of DDAVP can cause water intoxication.

Patient Monitoring

• Adjust treatment according to the patient's signs; the ideal dosage and frequency of DDAVP administration is based on water intake.
• Laboratory tests such as PCV, total solids, and serum sodium concentration to detect dehydration (inadequate DDAVP replacement)-usually not necessary

Prevention/Avoidance

Circumstances that might markedly increase water loss

Possible Complications

Anticipate complications of primary disease (pituitary tumor).

Expected Course and Prognosis

• The condition is usually permanent, except in rare patients in which the condition was trauma induced.
• Prognosis is generally good, depending on the underlying disorder.
• Without treatment, dehydration can lead to stupor, coma, and death.

Associated Conditions

N/A

Age-Related Factors

• Congenital CDI and NDI usually manifest before 6 months of age
• CDI related to pituitary tumors is usually seen in dogs >5 years old

Pregnancy/Fertility/Breeding

N/A

Synonyms

• Central diabetes insipidus
• Cranial diabetes insipidus
• ADH-responsive diabetes insipidus
• Nephrogenic diabetes insipidus

See Also

Hyposthenuria

Abbreviations

• ADH = antidiuretic hormone
• CDI = central diabetes insipidus
• DDAVP = brand name of desmopressin
• DI = diabetes insipidus
• MRI = magnetic resonance imaging
• NDI = nephrogenic diabetes insipidus
• PCV = packed cell volume
• PU/PD = polyuria/polydipsia

Client Education Handout Available Online