DIABETES MELLITUS

Diabetes Insipidus
Pronounced: diabetes -in-' sip-d-s
Definition
There are two forms of diabetes insipidus (DI): central diabetes insipidus (Central DI) and nephrogenic diabetes insipidus (NDI) .
Central DI is caused by inadequate antidiuretic hormone (ADH), whereas NDI is due to renal cells in the kidneys not responding to ADH.


Causes
ADH, also called vasopressin, controls the amount of water reabsorbed by the renal cells in the kidneys. ADH is made in the hypothalamus of the brain, while the pituitary gland , at the base of the brain, stores and releases ADH.
Pituitary Gland

• Central DI (up to 50% of cases, the cause is unknown) may be caused by:
o A lack of ADH made in the brain due to a genetic defect
o Damage to the hypothalamus or pituitary glands by surgery, infection, tumor, or head injury
o Sickle cell disease
• NDI may be caused by:
o Renal cells in the kidneys not being able to conserve water, which may be due to a genetic defect in some cases
o Kidney diseases (such as polycystic kidney disease )
o Medications (such as lithium, amphotericin B, or demeclocycline)—the most common cause of diabetes insipidus
Risk Factors
A risk factor is something that increases your chance of getting a disease of condition.
The following factors increase your chance of developing diabetes insipidus. If you have any of these risk factors, tell your doctor:
• Damage to the hypothalamus due to surgery, infection, tumor, or head injury
• Polycystic kidney disease or another kidney disease that may affect the filtration process
• Use of certain medications such as lithium, amphotericin B, or demeclocycline
• High blood levels of calcium
• Low blood levels of potassium
Symptoms
If you experience any of these symptoms, do not assume it is due to diabetes insipidus. These symptoms may be caused by other health conditions, such as diabetes mellitus, which is an entirely different condition. If you experience any one of them, see your doctor.
• Extreme thirst
• Frequent urination, especially during the night (nocturia)
• Dehydration
Diagnosis
Your doctor will ask about your symptoms and medical history, and perform a physical exam.
Tests may include the following:
• Blood Tests
o Electrolytes
o ADH levels
• Urinalysis
o Urine specific gravity and/or osmolality (measures how concentrated or dilute the urine is)
• Water Deprivation Test
o Only done under doctor supervision
o Urine output is measured for a 24-hour period
o Diabetes insipidus can cause as much as 4-10 liters of urine to be excreted per day
o Central DI – urine output is suppressed by a dose of vasopressin/ADH
o NDI – urine output is not suppressed by a dose of vasopressin/ADH
• Magnetic resonance imaging (MRI) of the head if CDI is suspected.
Treatment
Talk with your doctor about the best treatment plan for you. Treatment options include the following:
Central DI
1. A synthetic form of ADH is used. This drug could be taken by mouth, inhaled through the nose, or by injection.
2. In milder forms of central DI, a diuretic “water pill” or an antidiabetic medication could be used to boost the ADH effect on the renal cells in the kidney.
NDI
1. A diuretic “water pill” could be used.
2. If lithium is causing the problem, another diruectic, amelioride, could be used.
In both CDI and NDI, symptoms can often be reduced by decreasing the amount of sodium in the diet and by using medications called thiazide diuretics. Although diuretics typically increase urinary output, they conserve water loss and decrease urine output in people with diabetes insipidus.
Prevention
Diabetes insipidus is an uncommon condition. Although there are no known ways to prevent diabetes insipidus, it is wise to seek medical attention promptly if you have symptoms of excessive urination and thirst.

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