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To distinguish between partial DI and dipsogenic DI

There are two ways to distinguish partial pituitary DI from dipsogenic DI. The best way is to measure vasopressin during a fluid-deprivation hypertonic saline infusion test. The other is a brain MRI to determine if the posterior pituitary bright spot is present or absent.

Treatment for dipsogenic DI?

There is no completely satisfactory treatment for dipsogenic DI. If nocturia (the need o get up at night to urinate) is a problem it sometimes can be relieved by taking a small dose of DDAVP at bedtime. If DDAVP is taken during the day, it will reduce the thirst and urination but is also likely to produce water intoxication.

Partial pituitary DI is often difficult to distinguish from dipsogenic DI and it is much easier to treat. Therefore, you and your physician should be sure that you really have dipsogenic DI and not partial pituitary DI. There are several ways to do this. One is to measure the antidiuretic hormone during an osmotic stimulation test. A second is to do an MRI of the poster pituitary to see if the bright spot is present. The third is to try treatment with DDAVP to see how you respond. If you try the latter without first establishing the diagnosis by either of the first two methods, you should be watched closely, preferably in a hospital, in case you develop water intoxication.

It may get worse or it may get better as you get older. It is difficult to predict and will depend on what is causing it. Usually, however, the cause cannot be found on the MRI. In that case (called idiopathic), the DI usually does not get worse and often gets better with age.

Sodium imbalance’ seizures, means a low serum sodium concentration. This abnormality is usually referred to as ‘hyponatremia.’ When it develops in a patient taking DDAVP for DI, it usually indicates that the DI is due to abnormal thirst, an entity that we call ‘dipsogenic DI.’ Dipsogenic DI occurs in some patients with multiple sclerosis and is often confused with pituitary DI which is due to a deficiency of the antidiuretic hormone, vasopressin, and not to a thirst abnormality (although occasionally the two disorder occur together). These two types of DI¾ dipsogenic and pituitary¾ can be distinguished with certainty only by measuring antidiuretic hormone during a suitable stimulus such as a fluid deprivation test (although sometimes an MRI of the brain is also helpful)..

Two types of DI (pituitary and dipsogenic) can occur together but it is uncommon for them to do so. If you have ordinary uncomplicated pituitary DI, than DDAVP in doses sufficient to reduce your urine output completely to normal should also eliminate your thirst completely without producing symptoms or signs of water intoxication (low serum sodium). If you cannot take enough DDAVP to completely eliminate your excessive thirst without producing water intoxication, you probably have a form of primary polydipsia that is due to an abnormality in your thirst mechanism (dipsogenic DI).

When a patient with pituitary DI stops DDAVP, it is normal for polyuria (increased urination) to recur 2 to 3 hours before the thirst and polydipsia (increased drinking).If your are drinking excessively either because you have abnormal thirst or for some other reason. If the problem persists, you may want to switch from DDAVP to chlorpropamide since the later is less likely to induce hyponatremia. It is not clear why your dose requirements for DDAVP have decreased. It could be because you have developed hypothyroidism or hypoadrenalism. Therefore, you should have your plasma cortisol and thyroid hormone measured. If your MRI is really completely normal (i.e., the posterior pituitary bright spot is present), you cannot have pituitary DI and must have dipsogenic DI. The latter would be consistent with developing hyponatremia on DDAVP. Therefore, it is very important to determine if the posterior pituitary bright spot was seen. The other way to determine if you have dipsogenic or pituitary DI is measure plasma vasopressin during a fluid deprivation/hypertonic saline infusion test.

Source : Last Modified : 5/11/2002.
Compiled and edited by Editorial Team and approved by Expert Panel of DiabetoValens.com
In this Topic
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