Nephrogenic Diabetes Insipidus Health Article

Signs and symptoms

The primary symptoms for all types of NDI are generally the same: polyuria (excreting large amounts of dilute urine), and polydipsia, drinking excessive amounts of water, from 3–10 gal (12–38 L) per day. In infants born with NDI, symptoms begin to occur within a few days after birth. But since a child cannot verbally communicate its need for larger than normal amounts of water, parents, physicians, and other caregivers must be alert to other signs of the disorder. Overt signs include fever, irritability, and constipation, all of which may indicate dehydration. The child may also vomit often, be anorexic, and prefer water to milk. Other signs include rapid and severe dehydration if fluids are restricted or withheld, high levels of sodium and chloride in the blood, and urine that does not have a high specific gravity.

Elderly people, usually those with acquired NDI, may need close monitoring for symptoms especially if they are unable to communicate their need for lots of water, such as patients with Alzheimer disease or other mental deterioration. Also, elderly persons may be less sensitive to their need for water. Because of this, elderly persons with NDI can be more prone to dehydration, leading to such problems as infection, kidney failure, confusion, lethargy, and constipation.

For acquired NDI, close medical monitoring should be done for people at high risk for the disorder. These include people undergoing long-term treatment with lithium, and people with sickle cell anemia, chronic kidney failure, other kidney problems, very low blood levels of potassium and protein, and high blood levels of calcium.

Diagnosis

NDI is one of four types of diabetes insipidus (DI). In all four types, the basic symptoms are extreme thirst and excessive urination. Depending on other symptoms and conditions present in the patient, it can often be easy for a physician to suspect NDI. But additional tests are required to confirm it. These include a test of urine concentration to measure the ratio of osmotically active particles (such as sodium) to body water, a blood test to determine plasma concentrations, measuring urine volume, and a test to determine the level of the antidiuretic hormone AVP in blood plasma.

Sometimes physicians will have the patient take a water deprivation test to help determine the type of NDI present. In this test, the patient goes without water or other liquids for up to six hours. The blood plasma concentrations and urine volume are then measured. Even though a patient with NDI will become dehydrated during this test, the doctor monitors the patient's body weight and blood plasma osmolarity levels to insure they remain within safe parameters. At the end of the test, the patient is generally diagnosed with NDI if he or she has high levels of osmotically active particles in the blood and low levels of osmotically active particles in the urine.

The patient is also given desmopressin acetate (DDAVP), a synthetic version of AVP, to determine if the patient has a different form of DI called pituitary diabetes insipidus, also known as central diabetes insipidus. In addition, the physician measures heart rate and diastolic blood pressure to help determine whether the NDI is caused by defective AVPR2 genes or defective AQP2 genes.

Treatment and management

Although there is no cure for NDI, all forms of the disorder are treatable. Drinking plenty of water is the first and foremost treatment. Regardless of age of the patient, water must be available at all times. However, it is important for a child to maintain control of their NDI with medication so that they can eat, drink, and grow normally.

Medications used to treat NDI include one or a combination of indomethacin (Indocin), amiloride (Midamor), the thiazide diuretics hydrochlorothiazide (Hydrodiuril) or Chlorothiazide (Diuril), and occasionally desmopressin.

Management of NDI is also accomplished through restricting the intake of sodium and sometimes protein. Thiazide diuretics can reduce a patient's urine output, but they may also cause potassium depletion. Potassium supplements may be required. NDI that occurs during pregnancy usually goes away after delivery of the child. NDI caused by diet abnormalities are usually reversible once the diet becomes balanced. Acquired NDI caused by electrolyte imbalances such as low levels of calcium in the blood plasma or high levels of potassium in the blood plasma can be reversed once the imbalance is corrected.

In patients with lithium-induced NDI, thiazide diuretics are used cautiously since they reduce the kidneys' ability to excrete lithium. In many, but not all cases, people with lithium-induced NDI can improve when the dosage is decreased or stopped. In some cases, the lithium-induced NDI is irreversible.