Diabetes insipidus (DI) is a medical condition characterized by excessive urination. It is a fluid imbalance and the urine is very dilute and the person feels extremely thirsty. It is not the same disease as diabetes mellitus (DM), the type of diabetes related to blood sugar. Both are called diabetes, because of excessive urination. However, while people with DM urinate excessively because of high levels of blood sugar, DI results either from trouble with a part of the brain called the hypothalamus –in which case the condition is called central DI– or it results trouble in the kidney, in which case it is known as nephrogenic DI. There is also gestational DI, meaning a type of DI that develops specifically during pregnancy and then goes away after your baby is born, just like gestational DM. Gestational DI occurs in just 2-4 pregnancies out of 100,000.
Apart from producing gestational DI, pregnancy also can stress the body in a way that reveals central DI or nephrogenic DI that you have had for a while with mild symptoms. Finally, a fourth type of DI is called primary polydipsia. In this case, the main problem is that the person feels compelled to drink large amounts of water, while in the other types of DI the thirst is the result of the urine dilution. Primary polydipsia is further divided into two types. One type, called dipsogenic is a problem in the control of thirst. The other type, called psychogenic is a mental problem; the person feels that she must drink constantly.
Gestational DI is caused by the presence of high levels of an enzyme called vasopressinase, which is made in the placenta. This enzyme breaks down arginine vasopressin (AVP), a hormone that enables your kidneys to retain water in your body as opposed to eliminating it in the urine. With AVP continuously broken down, the kidneys cannot retain water, so the urine becomes very dilute and you become very thirsty. The condition is resolves after pregnancy, because you lose the placenta at delivery.
The first clue to diagnosing DI comes from your symptoms, particularly an excessive amount of urination, especially urination at night. In fact, it is common for people suffering from DI to wake up frequently to urinate, or to wet the bed. Since you lose body water if you have DI, you also likely will experience dry mount and dry skin, along with extreme thirst and water consumption. If you doctor thinks that you may have DI the volume of urine that you release each day will be recorded. If this volume is at least three liters, the doctor will order additional tests, such as measuring the level of AVP a blood sample. You will be asked to provide a urine sample to test what is called the osmolality, both before and after you are given a hormone that works like AVP. Along with confirming that you have DI, the results of these tests will allow doctors tell the difference between gestational DI and the other types of DI. Along the way, your blood will be tested for levels of special liver enzymes that can help determine whether you have a pregnancy complication called HELLP syndrome, which is one cause of DI. Additionally, DI can lead to dehydration, causing the quantity of amniotic fluid to decrease. This can slow the growth of the fetus and also cause premature labor and delivery. DI also can trigger a pregnancy complication called preeclampsia, which can put the fetus at risk by interrupting circulation of blood through the placenta.
Whether or not you are pregnant, DI can be treated with a medication called desmpressin (DDAVP). This is a synthetic hormone that produces effects similar to those of AVP. You can take DDAVP through the nose in mist form with no risk to you or the fetus. Unlike some other hormones, DDAVP is not broken down rapidy by the placenta. DDAVP also is safe in women who breastfeed, so you can continue taking it if you have a non-gestational form of DI that does not subside after you deliver your baby. Although DDAVP is the mainstay treatment for most DI, the medication tends not to work so well for nephronenic DI, the type of DI resulting from a problem in the kidney. In such cases, and in certain other cases, doctors may add drugs called sulfonylureas, or other medications, along with the DDAVP.