Diabetes Insipidus - Non-diabetic Diabetes
Although most people would have heard of diabetes mellitus or 'sugar diabetes' few would have come across the condition called diabetes insipidus. Part of their names may be the same, but any similarity between the two stops here since diabetes insipidus is a completely different and unrelated condition.
Many different hormones help to control metabolic activities within the body. One of these is called anti-diuretic hormone (ADH) and its function is to help control the balance of water in the body. It does this by regulating the production of urine. ADH is produced by the hypothalamus and then stored in the pituitary gland until it's needed. When diabetes insipidus (DI) exists the body either doesn't produce enough ADH or it doesn't respond correctly to the effects of ADH.
Symptoms
Someone with DI passes excessive amounts of urine and in a twenty-four hour period over three litres may be passed. They are always thirsty and find themselves drinking almost constantly. Disturbed sleep and disturbed daytimes are the consequence of having to pass water so frequently. In fact, throughout the day and night someone with DI may need to pass water every fifteen to twenty minutes.
Dehydration is common when DI is not recognised or treated causing the level of sodium in the blood to be too high. This in turn causes tiredness, lethargy, confusion, and the risk of fits and coma.
When babies and young children are affected in addition to the symptoms already described they may display failure to thrive.
Types
There are two forms of DI.
- The first is known as cranial DI and occurs because there is not enough ADH. It may develop as a result of a tumour in the hypothalamus or pituitary gland; following infection, radiotherapy, or surgery to the gland; or following a head injury.
- The second type is called nephrogenic DI and in this form the kidneys do not respond to ADH. This type may be caused by certain medicines; following kidney damage; or it may be present from birth having been inherited.
Diagnosis
Specific tests are performed when someone is suspected of having DI. These may include measuring:
- The volume of urine produced over a twenty-four hour period.
- The amount of urine produced after fluid input has been restricted - normally the amount of urine produced would be less under these circumstances, in DI large volumes are still produced.
- How the body responds to being given ADH - if this lowers the amount of urine produced then the cause is likely to be cranial DI, if the amount of urine remains high then nephrogenic DI is likely.
Scans are also used to identify specific causes of the two different types of DI that may also need treatment.
Treatment
If a treatable cause for the cranial DI is identified then it is treated and the DI usually resolves. Otherwise synthetic ADH is given on a daily basis to replace that which is lacking within the body.
Nephrogenic DI is treated with a low sodium diet and medication to reduce the amount of urine produced. Once again if an underlying cause is found and can be treated then nephrogenic DI will resolve.
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