The Differences between Diabetes Insipidus and Diabetes Mellitus

Trying to explain what diabetes Insipidus is can be challenging enough, without having it confused with "the other diabetes"-sugar diabetes (diabetes mellitus). Both share the word "diabetes" in the name, and both involve thirst and frequent urination, although in DI, urination is more frequent and in much greater volumes than the more common sugar diabetes, and the urine is subsequently extremely dilute and a very pale yellow color or almost clear. But beyond that, there's not much else in common. Some people with DI refer to their condition as either "central DI" or "nephrogenic DI" (depending on what's applicable), because it avoids the confusion caused when people not familiar with DI hear the word diabetes.

The more you know about both diabetes Insipidus and diabetes mellitus, the better able you are to explain your condition to others-from family members to primary care physicians or emergency technicians.

A good starting place is to know the meaning of the words themselves. Diabetes is derived from the Greek verb diabainein, which means to stand with legs apart, as in urination. Diabetes mellitus means, literally honey-sweet urine (back when doctors would sometimes actually taste people's urine to make a diagnosis). Diabetes Insipidus means bland or insipid urine.

There are four forms of DI: central DI (also referred to as pituitary or neurogenic DI), nephrogenic DI, gestational DI and dipsogenic DI. DI is caused by the lack of the antidiuretic hormone (vasopressin) or the kidney's inability to respond to this hormone.

Sugar diabetes, or diabetes mellitus, comes in two different forms: adult-onset diabetes and insulin-dependent diabetes. Sugar diabetes is caused by lack of the hormone insulin. Not only are DI and sugar diabetes separate conditions, but the diagnostic tests and treatments are different, as well.

The table below sums up the major differences:

	Central DI	Nephrogenic DI	Diabetes Mellitus
How common is the condition?	Uncommon	Uncommon	Common
What causes the condition?	The pituitary is unable to secrete vasopressin or the hypothalamus is unable to make vasopressin.	The kidneys are unable to respond to the diuretic hormone vasopressin. It is acquired (as in lithium-induced nephrogenic DI) or may be inherited, usually by male children.	Not enough of the hormone insulin is secreted, or the body's cells do not respond to it. Heredity, stress, obesity, pregnancy and drugs can also lead to diabetes mellitus.
What do these hormones do in our bodies?	Vasopressin is a diuretic hormone that controls water metabolism. It is made in the hypothalamus (a part of the brain) and is stored and secreted by the posterior pituitary gland (also in the brain).	It causes the kidney to reabsorb water. Water that is not absorbed is released to the bladder as urine.	Insulin is made in the pancreas, where it controls carbohydrate metabolism. It controls sugar (glucose) levels in the body.
How do I know if I have this condition?	Sudden or gradual urination of large amounts of clear, or almost colorless urine (polyuria), accompanied by excessive thirst (polydipsia). Dehydration can occur if fluid balance is not maintained.	Sudden or gradual urination of large amounts of clear, colorless urine (polyuria), accompanied by excessive thirst (polydipsia). Dehydration can occur if fluid balance is not maintained.	Excessive urination (polyuria), excessive thirst (polydipsia), excessive appetite (polyphagia). You may experience a sudden or gradual change with no symptoms. Other symptoms include tiredness, weight gain or loss, and skin infections that do not heal.
How is the condition diagnosed?	Water deprivation test/vasopressin test. Also, MRI to determine if the post pituitary bright spot is present.	Water deprivation test/vasopressin test.	Fast blood sugar-24hr. post-prandial test. Glucose tolerance test.
How is the condition managed?	Balance fluid intake and urine output. Replace antidiuretic hormone, vasopressin (usually with synthetic hormone: desmopressin), find, if possible, underlying injury to pituitary gland that is causing the condition.	Balance urine output with fluid intake. Treatment with thiazide and potassium-sparing diuretics. Low-sodium diet (500-600 mg/day or less for adults; 300 - 500 mg/day for children).	Correct sugar/insulin intake. Prevent progression of disease. Change the diet. Oral medication.