(See also Central Diabetes Insipidus Central Diabetes Insipidus Diabetes insipidus results from a deficiency of vasopressin (antidiuretic hormone [ADH]) due to a hypothalamic-pituitary disorder (central diabetes insipidus) or from resistance of the kidneys... read more .)
NDI is characterized by inability to concentrate urine in response to vasopressin. Central diabetes insipidus is characterized by lack of vasopressin. Either type of diabetes insipidus may be complete or partial.
Etiology of NDI
NDI can be
The most common inherited NDI is an X-linked trait with variable penetrance in heterozygous females that affects the arginine vasopressin (AVP) receptor 2 gene. Heterozygous females may have no symptoms or a variable degree of polyuria and polydipsia, or they may be as severely affected as males.
In rare cases, NDI is caused by an autosomal recessive or autosomal dominant mutation that affects the aquaporin-2 gene and can affect both males and females.
Acquired NDI can occur when disorders (many of which are tubulointerstitial diseases Overview of Tubulointerstitial Diseases Tubulointerstitial diseases are clinically heterogeneous disorders that share similar features of tubular and interstitial injury. In severe and prolonged cases, the entire kidney may become... read more ) or drugs disrupt the medulla or distal nephrons and impair urine concentrating ability, making the kidneys appear insensitive to vasopressin. These disorders include the following:
Autosomal dominant polycystic kidney disease Autosomal Dominant Polycystic Kidney Disease (ADPKD) Polycystic kidney disease (PKD) is a hereditary disorder of renal cyst formation causing gradual enlargement of both kidneys, sometimes with progression to renal failure. Almost all forms are... read more
Nephronophthisis Nephronophthisis and Autosomal Dominant Tubulointerstitial Kidney Disease (ADTKD) Nephronophthisis and autosomal dominant tubulointerstitial kidney disease (ADTKD) are inherited disorders that cause cysts restricted to the renal medulla or corticomedullary border and, eventually... read more and medullary cystic kidney disease complex
Sickle cell nephropathy
Release of obstructing periureteral fibrosis
Many drugs, especially lithium, but also others (eg, demeclocycline, amphotericin B, dexamethasone, dopamine, ifosfamide, ofloxacin, orlistat)
Possibly chronic hypokalemic nephropathy
Acquired NDI can also be idiopathic. A mild form of acquired NDI can occur in any patient who is older or sick or who has acute or chronic renal insufficiency.
In addition, certain clinical syndromes can resemble NDI:
The placenta can secrete vasopressinase during the 2nd half of pregnancy (a syndrome called gestational diabetes insipidus).
After pituitary surgery, some patients secrete an ineffective ADH precursor rather than vasopressin.
Symptoms and Signs of NDI
Generation of large amounts of dilute urine (3 to 20 L/day) is the hallmark. Patients typically have a good thirst response, and serum sodium remains near normal. However, patients who do not have good access to water or who cannot communicate thirst (eg, infants, older patients with dementia) typically develop hypernatremia Hypernatremia Hypernatremia is a serum sodium concentration > 145 mEq/L (> 145 mmol/L). It implies a deficit of total body water relative to total body sodium caused by water intake being less than water... read more due to extreme dehydration. Hypernatremia may cause neurologic symptoms, such as neuromuscular excitability, confusion, seizures, or coma. Ureteral dilation is rare but can occur in severe cases with high urine volumes.
Diagnosis of NDI
24-hour urine volume and osmolality
Water deprivation test
NDI is suspected in any patient with polyuria Polyuria Polyuria is urine output of > 3 L/day; it must be distinguished from urinary frequency, which is the need to urinate many times during the day or night but in normal or less-than-normal volumes... read more . In infants, polyuria may be noticed by the caregivers; if not, the first manifestation may be dehydration.
Initial testing includes 24-hour urine collection (without fluid restriction) for volume and osmolality, and serum electrolytes.
Patients with NDI excrete > 50 mL/kg of urine/day (polyuria). If urine osmolality is < 300 mOsm/kg (300 mmol/L; known as water diuresis), central diabetes insipidus Central Diabetes Insipidus Diabetes insipidus results from a deficiency of vasopressin (antidiuretic hormone [ADH]) due to a hypothalamic-pituitary disorder (central diabetes insipidus) or from resistance of the kidneys... read more or NDI is likely. With NDI, urine osmolality is typically < 200 mOsm/kg (200 mmol/L) despite clinical signs of hypovolemia (normally, urine osmolality is high in patients with hypovolemia). If osmolality is > 300 mOsm/kg (300 mmol/L), solute diuresis is likely. Glucosuria and other causes of solute diuresis must be excluded.
Serum sodium is mildly elevated (142 to 145 mEq/L, or 142 to 145 mmol/L) in patients with adequate free water intake but can be dramatically elevated in patients who do not have adequate access to free water.
Water deprivation test
The diagnosis is confirmed by a water deprivation test, which assesses the maximum urine concentrating ability and response to exogenous vasopressin.
During the test, urine volume and osmolality are measured hourly and serum osmolality is measured every 2 hours. After 3 to 6 hours of water deprivation, the maximal osmolality of urine in patients with NDI is abnormally low (< 300 mOsm/kg, or 300 mmol/L). NDI can be distinguished from central diabetes insipidus (lack of vasopressin) by administering exogenous vasopressin (aqueous vasopressin 5 units subcutaneously or desmopressin 10 mcg intranasally) and measuring urine osmolality. In patients with central diabetes insipidus Central Diabetes Insipidus Diabetes insipidus results from a deficiency of vasopressin (antidiuretic hormone [ADH]) due to a hypothalamic-pituitary disorder (central diabetes insipidus) or from resistance of the kidneys... read more , urine osmolality increases 50 to 100% over the 2 hours after administration of exogenous vasopressin (15 to 45% in partial central diabetes insipidus). Patients with NDI usually have only a minimal rise in urine osmolality (< 50 mOsm/kg [50 mmol/L]; up to 45% in partial NDI).
Prognosis for NDI
Infants with inherited NDI may develop brain damage with permanent intellectual disability if treatment is not started early. Even with treatment, physical growth is often delayed in affected children presumably because of frequent dehydration. All complications of NDI except for ureteral dilation are preventable with adequate water intake.
Treatment of NDI
Adequate free water intake
Restriction of dietary salt and protein
Correction of the cause
Sometimes a thiazide diuretic, a nonsteroidal anti-inflammatory drug (NSAID), or amiloride
Treatment consists of ensuring adequate free water intake; providing a low-salt, low-protein diet; and correcting the cause or stopping any likely nephrotoxin. Serious sequelae are rare if patients can drink at will.
If symptoms persist despite these measures, drugs can be given to lower urine output. Thiazide diuretics (eg, hydrochlorothiazide 25 mg orally once or twice/day) can paradoxically reduce urine output by diminishing water delivery to vasopressin-sensitive sites in the collecting tubules. NSAIDs (eg, indomethacin) or amiloride can also help.
Patients with NDI are unable to concentrate urine due to impaired renal tubule response to vasopressin.
They typically pass large volumes of dilute urine, are appropriately thirsty and have near-normal serum sodium levels.
Minimize preventable neurologic sequelae by considering inherited NDI in infants with polyuria or affected family members.
Measure 24-hour urine volume and osmolality and serum electrolytes.
Confirm the diagnosis with a water deprivation test.
Ensure adequate free water intake, restrict dietary salt and protein, and use a thiazide diuretic or amiloride as needed.