Encyclopedia of Health and Medicine

diabetes insipidus 123
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 dysfunction
of INSULIN. Diabetes insipidus is a dysfunction
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 BRAIN where the hypothalamus and pituitary
gland are located. Such trauma may as a consequence
of accidental injury (TRAUMATIC BRAIN
INJURY), STROKE, or surgery. The hypothalamus may
release inadequate amounts of ADH or the pituitary
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 FAILURE the kidneys
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 MEDICATIONS demeclocycline
and amphotericin B, are the most common
culprits when NDI is DRUG induced.
Symptoms and Diagnostic Path
Whether central or nephrogenic, diabetes insipidus
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 diabetes
insipidus to drink and urinate up to 20 liters
or more every 24 hours. When symptoms develop
gradually and water intake keeps pace with urination,
the person may not experience the symptoms
as unusual events. Diabetes insipidus results
in health complications (such as electrolyte imbalance)
only when the person is unable to match
fluid input and output. The diagnostic path is primarily
clinical (based on symptoms) with a water
deprivation test to confirm the diagnosis. For this
test, the person remains under continuous medical
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
GLUCOSE and INSULIN levels. The endocrinologist
may also choose to conduct diagnostic imaging
procedures such as MAGNETIC RESONANCE IMAGING
(MRI) or COMPUTED TOMOGRAPHY (CT) SCAN to 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 THERAPY with 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 condition
results in kidney damage over time. Treatment
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 DISEASE are commonly the cause
of NDI. Appropriately treating these disorders mitigates
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.