Diabetes Insipidus versus Diabetes Mellitus
Even though diabetes insipidus and diabetes mellitus have similar names and even share some symptoms, they have very different causes.
The disease known as diabetes mellitus is related to the hormone called insulin, and to its effects on blood sugar levels. People with this disease either don’t produce insulin, or are resistant to insulin, meaning that the hormone cannot do its job of allowing cells to take up glucose to use as energy. As a result, blood sugar levels are uncontrolled.
In contrast, diabetes insipidus is typically related to a hormone called vasopressin, which regulates how much water the kidneys excrete. Vasopressin is an anti-diuretic hormone, which means it prevents water excretion by the kidneys. In people with diabetes insipidus vasopressin is either not produced, or kidney cells are resistant to vasopressin and cannot respond to it normally. As a result, the anti-diuretic effect of vasopressin is not exerted, causing the kidneys to excrete more water than normal.
Symptoms and Signs of Diabetes Insipidus
The defining characteristics of diabetes insipidus are intense thirst and craving for water, and vastly increased urine output. These two signs can be accompanied by several others, depending on the age of the person with the disease.
For adults with access to plenty of drinking water, the signs of the disease are limited to excessive thirst and urination. There is the potential for dehydration if the water supply is interrupted.
Children with diabetes insipidus have increased thirst and urination just as adults do, but often the pattern of accompanying signs and symptoms is different. Very young children with this disease tend to have soaking wet diapers even a short time after they have been changed, due to uncontrollable high urine output. Older children are highly likely to be chronic bed-wetters.
In addition, children are at much higher risk of dehydration. Children are likely to be irritable or listless, and often have fever, along with vomiting or constipation.
Complications of Diabetes Insipidus
These symptoms and signs of diabetes insipidus are caused by the increased excretion of water by the kidneys. Complications of the disease are the result of dehydration and the physical problems it causes.
Adults with this disease are capable of quenching their thirst as long as water is available and are therefore at lower risk of dehydration than children are. Even so, dehydration is still a risk which must be considered. Fresh water should always be available, and hot weather should be avoided. In addition, extreme physical exertion should be avoided, especially in hot weather.
Dehydration and the accompanying electrolyte imbalance can cause irritability, fatigue, headaches, muscle pains, rapid heart rate, and dry skin.
In young children, the complications of diabetes insipidus are potentially very severe. Possible complications include physical and mental developmental delay, seizures, and physical and mental disability. All of these complications are the result of chronic dehydration, and the chronic malnutrition that can accompany it.
James CM Chan, MD, for eMedicine: Diabetes Insipidus
National Institute of Health Kidney and Urologic Diseases Information: Diabetes Insipidus
National Institute of Health MedlinePlus: Diabetes Insipidus