Diabetes insipidus - Brain: the inside story

Brain: the inside story
Factsheet:
Diabetes insipidus
General worksheet
on brain structure and function (answers)
George has diabetes insipidus, a rare condition brought about as
a result of the head injury he sustained on the building site. He has
a raging thirst and passes far too much dilute pale urine. This
happens even when he is dehydrated and should be trying to
conserve fluid.
Diabetes insipidus is not to be confused with diabetes
mellitus, which is a condition where the amount of blood
glucose is too high because the pancreas does not produce
enough insulin to help get the glucose into the body’s cells.
The word ‘diabetes’
comes from the
Greek, meaning
DID YOU
T
‘siphon’, because
KNOW?
people with the
condition passed so much urine
they were like siphons.
It’s used to describe conditions
that cause excessive urination.
?
The symptoms of diabetes insipidus are similar to those of diabetes mellitus, but there is no sugar
present in the urine and blood sugar levels are normal.
What is diabetes insipidus?
Diabetes insipidus occurs when not enough anti-diuretic hormone (ADH) (vasopressin) reaches
the kidneys. ADH is needed to stop the kidneys producing too much urine.
The hypothalamus works in tandem with the pituitary gland. They are responsible for
osmoregulation (water control) in the body, and they signal to the kidneys with ADH. The
hypothalamus makes ADH and the pituitary gland releases it. Diabetes insipidus occurs either:
쎲 when the hypothalamus does not secrete enough anti-diuretic hormone (cranial diabetes
insipidus)
the hypothalamus is producing enough anti-diuretic hormone but the kidneys do not
respond to it (nephrogenic diabetes insipidus)
쎲 or when
Both cranial and nephrogenic diabetes insipidus make the kidneys unable to retain water.
What are the symptoms of diabetes insipidus?
쎲 passing large amounts of urine – between three and 20 litres per day!
쎲 frequent urination, day and night – at least every half an hour
쎲 raging thirst, despite drinking lots
쎲 dehydration
쎲 tiredness
What causes diabetes insipidus?
Cranial diabetes insipidus can be as a result of:
쎲 head injuries (like George’s)
쎲 surgery (it may only be short-term)
쎲 tumours
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Brain: the inside story
Factsheet:
Diabetes insipidus
General worksheet
on brain structure and function (answers)
쎲 infections (such as tuberculosis)
쎲 something unknown (idiopathic)
Nephrogenic diabetes insipidus can be as a result of:
쎲 amyloidosis (abnormal protein deposits in the kidneys)
쎲 polycystic kidneys (small cysts in the kidneys)
쎲 drugs, like lithium
쎲 genetic disorders (rare)
How is diabetes insipidus diagnosed?
쎲 blood and urine tests can indicate diabetes insipidus
쎲 a water deprivation test – this is what George had. He went into hospital early and was
deprived of all fluids. Blood and urine tests were done hourly to measure the sodium levels,
together with blood pressure, weight and the quantity of urine passed. His blood sodium and
potassium levels were higher than normal, and his urine sodium and potassium levels were very
low, indicating diabetes insipidus
쎲 an injection of ADH – if this stops the production of urine, the patient may have cranial diabetes
insipidus. If it does not, it suggests nephrogenic diabetes insipidus
쎲 an MRI scan – where cranial diabetes insipidus is suspected,
to check for any obvious abnormality in the hypothalamus
(which makes ADH) or pituitary gland (which releases ADH)
How is cranial diabetes insipidus treated?
쎲 mild cases may be treated by simply drinking enough water
to keep blood salt levels stable
쎲 with the drug desmopressin, a synthetic form of ADH
MRI scanner
How is nephrogenic diabetes insipidus treated?
쎲 mild cases may be treated by drinking enough water to keep blood salt levels stable, and following
a diet lower in salt and protein
쎲 with a drug that reduces the amount of urine produced by the kidneys, e.g. hydrochlorothiazide.
Desmopressin would not work
And what about George? George’s MRI scan showed that his head injury was healing well,
so he was given desmopressin for a few months to ease his diabetes insipidus, after which he
made a full recovery.
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