DI isn’t as well known as Type 1 and Type 2, but you should know about it.
Unrelated to the more common diabetes mellitus, DI is a serious condition which occurs when the brain doesn’t produce enough antidiuretic hormone (ADH, also known as arginine vasopressin or AVP), called ‘cranial DI’, or the kidneys don’t respond to normal levels of ADH called ‘nephrogenic DI’.
There are 2 other types of DI in pregnancy, ‘gestational DI’ and problems with thirst regulation, ‘dipsogenic DI’. There are many causes of all types of diabetes insipidus, including infections, certain medications, blood disorders and head injuries or tumours, but for some, the cause is unknown or may be genetic. It can occur at any age, affecting 1 in 25,000. All types result in an inability to concentrate urine, so patients pass very large volumes of dilute urine.
These include excessive thirst and passing urine frequently, dehydration, tiredness and other symptoms related to the actual cause. In infants, the first sign may simply be a failure to thrive with poor growth, whilst in adults the development may be so slow that it isn’t recognised for some time. Various complex tests will be needed to make the diagnosis, including blood tests, a 24-hour urine collection and concentration analysis, brain MRI and kidney tests such as ultrasound or an intravenous pyelogram. Tests specific to a possible cause may also be indicated.
This depends on whether a specific cause is found and so treating that. For example, if a patient is on a drug known to cause it, such as lithium, an alternative should be found.
With a diagnosis of cranial DI, if the condition is only mild, simply drinking a little more to prevent thirst may be enough. Otherwise a replacement hormone, desmopressin, can be given as tablets, injection or as a nasal spray.
However, this drug risks low blood sodium levels so it needs monitoring by a specialist and regular blood tests. In nephrogenic DI, again simply monitoring fluid intake may be enough or desmopressin may be used. For more severe cases a variety of drugs have been used including thiazide-type diuretics and non-steroidal anti-inflammatory drugs. The prognosis will depend on the cause, but is generally good, once treatment or correct fluid management have been started.
E362 – DI, The Other Diabetes- www.dibetic.today