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Diabetes Insipidus

Diabetes insipidus is a health disorder characterized by intense thirst and the excretion of excessive volumes of diluted urine (polyuria). Even though Diabetes Insipidus sounds similar to Diabetes Mellitus (“sugar diabetes”) and some symptoms are the same, they are completely unrelated conditions. Most cases of Diabetes Insipidus (DI) are caused by the inadequate production, storage or release of the hormone Antidiuretic Hormone (ADH) or Vasopressin which is responsible for increasing water absorption by the kidneys and decreasing urine flow. This form of DI is also known as Central Diabetes Insipidus or Neurogenic Diabetes Insipidus. Less common causes of DI include Nephrogenic Diabetes Insipidus where the kidneys do not respond to the hormone Vasopressin and Gestational Diabetes Insipidus which occurs during pregnancy.

The two most common symptoms of DI are Extreme or Intense thirst and Excessive excretion of large volumes of diluted urine. The urine output varies based on the severity of the condition and could range from 2.5 litres per day in mild DI to 15 litres per day in severe DI associated with the consumption of large volumes of fluid. The normal adult urinary output is 1.5 to 2.5 litres per day. Other symptoms may include bed-wetting and the need to get up several times during the night to urinate (nocturia). Infants and young children with DI may present with symptoms such as inconsolable crying, unexplained fussiness, fever,diarrhoea, vomiting, unusually wet diapers, dry skin and cool extremities.

The kidneys normally remove excess body fluids from the bloodstream which is stored in the bladder as urine before excretion. When the body’s fluid regulatory system is working properly, the kidneys produce less urine to help conserve body fluid in response to reduced fluid intake or dehydration. To maintain body fluid balance and composition, fluid intake is influenced by thirst and habit while the rate of excretion is under the influence of Antidiuretic Hormone (ADH) also known as Vasopressin. ADH is produced in the hypothalamus and is stored in the pituitary gland at the base of the brain. This hormone is released into the bloodstream when necessary and concentrates the urine by triggering the kidney tubules to reabsorb water into the bloodstream.

Central DI is caused by damage to the pituitary gland or hypothalamus as a result of head injury, tumour, meningitis, inflammation or surgery. This damage disrupts the normal production, storage and release of ADH and in some cases the cause is unknown. Nephrogenic DI occurs when there is a defect in the kidney tubules and hence the inability to respond to ADH. This defect may be genetic (usually more common in males), due to chronic kidney disease or the ingestion of certain drugs such as Lithium or Tetracycline. In 25% of cases, the cause of Nephrogenic DI is unknown. Gestational DI occurs only during pregnancy when an enzyme made by the placenta destroys ADH in the mother.

A doctor should be consulted immediately symptoms of extreme thirst and excessive urination are noticed. Your doctor may perform a series of tests such as a Water Deprivation Test where the patient is asked to stop taking fluids 2 to 3 hours before the test to measure changes in body weight, urinary output and urine compostion when fluids are restricted. The blood level of ADH may also be measured. In children, the water deprivation test has to be closely monitored to ensure that they do not lose more than 5% of their body weight during the test. Urinalysis which is the physical and chemical examination of the urine shows diluted urine in DI. A Magnetic Resonance Imaging (MRI) scan of the head may show abnormalities in and around the pituitary gland and Genetic Screening may be carried out when there is a positive family
history.

DI may cause dehydration and electrolyte (minerals such as Sodium, Potassium and Calcium in blood) imbalance which may lead to muscle weakness, dry mouth, low blood pressure (hypotension), fever, headache, sunken eyes, weight loss, fatigue and rapid heart rate.

Treatment depends on the form of DI diagnosed. Central DI is treated with a synthetic form of ADH known as Desmopressin which may be administered as nasal spray, oral medications or injectables. The underlying cause is treated first however. In mild cases of DI, adequate fluid consumption may be all the treatment necessary. Nephrogenic DI is treated with adequate water intake to avoid dehydration, low salt intake to help reduce urine
production and paradoxically, a diuretic known as hydrochlorthiazide can reduce urinary output in some cases. If the use of certain medications is found to be the cause of DI, they should be discontinued under the supervision
of your doctor. Gestational DI is treated with Desmopressin.

It is important for patients with DI to prevent dehydration by consuming prescribed volumes of fluids. Patients
should always carry water on them in case a situation arises when water or fluids are not readily available.


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