quence of kidney disease (nephrogenic diabetes
insipidus, or NDI).
A DIFFERENT DIABETES
Diabetes insipidus has no relationship to the
familiar and common form of DIABETES, known
clinically as diabetes mellitus, which is a dys-
function of INSULIN. Diabetes insipidus is a dys-
function of ANTIDIURETIC HORMONE(ADH). To avoid
confusion, doctors commonly refer to diabetes
insipidus as CDI (central diabetes insipidus) or
NDI (nephrogenic diabetes insipidus).Central Diabetes Insipidus (CDI)
CDI may result from lesions (growths) that affect
the function of the hypothalamus, though more
commonly as a result of trauma to the region of
the BRAINwhere the hypothalamus and pituitary
gland are located. Such trauma may as a conse-
quence of accidental injury (TRAUMATIC BRAIN
INJURY), STROKE, or surgery. The hypothalamus may
release inadequate amounts of ADH or the pitu-
itary gland may fail to respond. CDI may also
occur when an ADENOMA(noncancerous tumor)
grows in the posterior lobe of the pituitary gland
and inhibits ADH secretion.
Nephrogenic Diabetes Insipidus (NDI)
In severe kidney disease or RENAL FAILUREthe kid-
neys themselves do not respond to ADH. This
leaves the kidneys unable to concentrate the
urine. They consequently pass into the urine as
much water as passes through them in the blood.
Medications that interfere with kidney function
may cause NDI. Lithium, taken to treat BIPOLAR
DISORDER, and the ANTIBIOTIC MEDICATIONSdemeclo-
cycline and amphotericin B, are the most common
culprits when NDI is DRUGinduced.
Symptoms and Diagnostic Path
Whether central or nephrogenic, diabetes insipi-
dus symptoms are the same. They are
- extreme thirst (called polydipsia) and often a
craving for ice water - frequent urination (called polyuria), including
through the night (NOCTURIA)
It is not uncommon for a person who has dia-
betes insipidus to drink and urinate up to 20 liters
or more every 24 hours. When symptoms develop
gradually and water intake keeps pace with urina-
tion, the person may not experience the symp-
toms as unusual events. Diabetes insipidus results
in health complications (such as electrolyte imbal-
ance) only when the person is unable to match
fluid input and output. The diagnostic path is pri-
marily clinical (based on symptoms) with a water
deprivation test to confirm the diagnosis. For this
test, the person remains under continuous med-
ical observation while consuming no water.
Hourly urine tests measure the concentration of
the urine. In a healthy person the urine becomes
increasingly concentrated with restricted fluid
consumption. In diabetes insipidus the urine
remains dilute.
Because excessive thirst and urination are also
symptoms of diabetes mellitus, the endocrinologist
is likely to conduct blood tests to measure blood
GLUCOSEand INSULIN levels. The endocrinologist
may also choose to conduct diagnostic imaging
procedures such as MAGNETIC RESONANCE IMAGING
(MRI) or COMPUTED TOMOGRAPHY(CT) SCANto identify
traumatic injury or tumors in CDI.Treatment Options and Outlook
Treatment targets any identified underlying cause.
Thiazide diuretic medications, which ordinarily
increase urination, have the opposite effect in
both CDI and NDI because of their actions on the
kidneys. HORMONE THERAPYwith medications such
as desmopressin or lypressin nasal spray is usually
effective for CDI. Even when the person is able to
maintain fluid balance, it is important to treat
diabetes insipidus because the untreated condi-
tion results in kidney damage over time. Treat-
ment minimizes or eliminates symptoms for most
people.Risk Factors and Preventive Measures
The primary risk factor for CDI is head trauma, in
which case early intervention and treatment are
most effective. Chronic kidney disorders such as
POLYCYSTIC KIDNEY DISEASEare commonly the cause
of NDI. Appropriately treating these disorders mit-
igates the NDI. It is important for people who
have CDI or NDI to drink enough water to remain
hydrated, to prevent complications arising from
electrolyte imbalance.diabetes insipidus 123