The causes of diabetes insipidus include
neurosurgery or head trauma,
pituitary mass lesions, and infiltrative disorders
of the pituitary like sarcoidosis.
It is an inadequate production
of antidiuretic hormone
by the posterior
In the presence of ADH,
aquaporin water channels are inserted
into the collecting tubules
and allow water to be reabsorbed.
In the absence of ADH, excessive water
is excreted by the kidneys.
Excretion of more than three liters of urine per day
is considered polyuria.
The severity of diabetes insipidus varies
with the completeness of the deficiency.
Patients describe mild to extreme polyuria
and corresponding thirst,
and partial diabetes insipidus
Frank hypernatremia is unusual
develop extreme thirst
and with free access to water,
they can maintain
their serum sodium
in the high normal range.
When patients do not drink enough
to replace water lost in the urine
due to poor or absent thirst drive
or lack of free access to water,
they develop hypernatremia.
In the patient with polyuria,
diabetes insipidus is diagnosed
with a simultaneous lab evidence of
inability to concentrate urine
in the face of elevated
and osmolarity with inappropriately
low urine osmolarity.
If necessary, a water deprivation test
can be performed.
The treatment of DI consists of
the infusion of desmopressin
otherwise known as DDAVP.
This can be administered intranasally
Let's revise the clinically significant
pituitary hormones deficiency states.
In the case of ACTH and cortisol,
the initial test
is a simultaneous ACTH
and cortisol test.
The causes of the deficiency include
exogenous oral, intravenous,
or topical steroid supplementation
the hypothalamic pituitary axis.
In the case of TSH, T4, and T3,
the initial test is
a simultaneous TSH
and free T4 evaluation.
Remember that you can't use
a TSH response to monitor therapy
because of the secondary nature
of the hypothyroidism.
With regards to growth hormone,
the test is insulin-derived growth factor 1
and a growth hormone-releasing
or water deprivation test can be used
to confirm the diagnosis.
In the case of luteinizing hormone
and follicle-stimulating hormone,
simultaneously checking both hormones,
and a total testosterone in a male
and estradiol in a female
will help making the diagnosis.
The causes of these deficiencies
are in those patients
who have known
or in women
who exercise excessively,
have severe illness
or severe infection.
Let’s talk about the workup
of a pituitary mass.
This first step is to determine
whether or not the mass
is causing any mass effect
and clinical symptoms.
Also, is the mass secreting
and finally, whether the mass
has a propensity to grow
and cause problems
in the future?
Benign pituitary adenomas are the most
common tumor of the pituitary gland.
The tumors of less than one centimeter
are defined as microadenomas
and tumors larger than one centimeter
are termed macroadenomas.
Incidentally, noted pituitary
tumors are common.
Biochemical testing informed by findings
on history and physical exam
is a much more
cost effective approach.
Initial tests for pituitary incidentally noted
masses include an 8 AM cortisol level,
a thyroid-stimulating hormone level,
a T4, a prolactin level, and an IGF-1.
The mass effects of pituitary tumors
mainly manifest as headache.
Pituitary masses can also compress
the normal pituitary gland
causing hormone deficiencies.
A large pituitary mass
can cause panhypopituitarism
which is the impaired secretion
of all pituitary hormones.
The optic chiasm, just superior
to the pituitary gland,
in a large pituitary mass,
may be compressed
a result in loss of vision.
Mild peripheral vision loss may
manifest as bitemporal hemianopsia
and progress on to
usually as the tumor expands and
compresses more of the optic chiasm.
Visual field testing is a sensitive
measure of optic nerve damage
and should be evaluated
by an ophthalmologist.
Seizures and neurologic manifestations
and invasion of the cavernous sinus
cause damage to the cranial nerves
particularly three, four, and six.
These are the ones that pass
through the cavernous sinus
and may manifest with diplopia and
extraocular muscle palsies or paralysis.
Let's talk about the treatment of
clinically nonfunctioning pituitary tumors.
In nonfunctioning pituitary tumors
that cause a mass effect,
we need to remove
them by surgery.
The most common surgical approach
is the transsphenoidal approach
which takes place through
the nares or the mouth.
Indications for surgery
include mass effect
particularly if there's
a visual field defect,
a tumor that abuts
the optic chiasm,
or an invasive tumor
invading into the brain
or cavernous sinus,
and a tumor close to
the optic chiasm
in a patient who plans
to become pregnant
because with the
of the pituitary
that smaller tumor may increase
and impinge on the optic chiasm.
The empty sella syndrome is diagnosed
when the normal pituitary gland
is not visualized
or is excessively small on MRI.
It is a radiologic finding rather than
a distinct clinical condition.