Diabetes insipidus (DI) is a condition caused by the deficiency
of or resistance to the action of anti-diuretic hormone (ADH),
which is produced in the posterior pituitary gland and secreted via
the hypothalamus (part of the brain).
The purpose of ADH is to prevent too much water loss through the
urine by concentrating it. The hormone acts on the kidney tubules
to re-absorb salt and water. If there is a deficieny of this
hormone or if the kidney fails to respond well to the hormone, you
will pass out alot of dilute urine, hence diabetes (passing out
lots of urine) insipidus (insipid: plain, not salty).
There are many types but in general they fall into 2 groups.
Central DI is due to a deficiency of production of ADH, which can
be due to many reasons, from a tumour to trauma eg. operation or
head injury. Nephrogenic DI is due to a resistance of the kidney to
the effect of the hormone. Some forms of nephrogenic DI are due to
inherited mutations: perhaps that is what your doctor is
suspecting. There are effective treatment of this condition by
replacing the hormone or simply by consuming more water and
salt.
As for medical fitness, if you have this condition (and it is
proven by various lab tests), then chances are that you may be
downgraded. The risk in the army would be heat exhaustion. Since
patients with DI cannot concentrate their urine, they will lose
excessive fluids and run a greater risk of heat injury. That is not
a problem if you have plenty of fluids and salts but obviously that
is not always possible in millitary operations.
You may find snippets of medical information at Road Health Centre
forum below. I am posting this reply there as well in case others
are interested.
http://www.sgforums.com/?action=forum_display&forum_id=2215
