Diabetes Insipidus

Diabetes insipidus (DI) is a disorder when the kidneys are incompetent to conserve water typically resulting to too much thirst and large urine volume. ^[1] Although it shares name with another disease called diabetes mellitus, the two are essentially poles apart from each other and are not related. ^[2]

Epidemiology

Records show a prevalence of 3 per 100,000 in the United States. Males and females are equally affected. ^[3]

Causes

Antidiuretic hormone or vasopressin is a chemical substance being generated by a brain structure termed hypothalamus. This is stored within a gland called pituitary gland which is situated at the base of the brain. The said hormone is vital in the body’s water management thru its action on the kidneys.

Two major types of DI exist. Central type refers to the condition when there is diminished secretion of a hormone called antidiuretic hormone (ADH). The second is called nephrogenic type when resistance to ADH action in the kidney is present. 

Central DI can be brought about by injuries to the aforementioned brain structures such as in head trauma, surgery and infectious processes. ^[1] Inflammation and autoimmunity are being recognized to have a role in the pathophysiology of the disease. The condition can likewise arise when there are tumors such as in craniopharyngiomas and germinomas. Other causes include granulomatous diseases like sarcoidosis, anorexia nervosa, vascular lesions such as sickle cell disease and Sheehan syndrome, cancer metastasis and hypoxic encephalopathy. 

Nephrogenic DI can be caused by hypokalemia, pregnancy, kidney disorders and hyperglycemia. Some drugs that can cause it include lithium, amphotericin B, orlistat and foscarnet. The hereditary type is rare with most cases affecting males. ^[3]

Signs and Symptoms

The affected person experiences extreme thirst which can be uncontrollable. Another main manifestation is having large amount of urine which is often dilute and colorless. Increased frequency of urination is noted especially at night. The patient may have dry skin and constipation. ^{[1] [4]}

Diagnosis

After getting the patient’s medical history and performing a physical examination, the physician often requests for laboratory exams such as urinalysis, water deprivation tests and imaging tests of the brain like CT scan and MRI. ^[4]

Treatment

Treatment depends on the cause. Usually for central DI, vasopressin or desmopressin is prescribed. This can be in the form of nasal spray, oral tablet or injectable medicine. Nephrogenic DI is frequently treated using diuretics such as hydrochlorothiazide and anti-inflammatory drugs.  ^{[1] [5]}

References:

1.      http://www.nlm.nih.gov/medlineplus/ency/article/000377.htm.

2.      http://www.mayoclinic.com/health/diabetes-insipidus/DS00799

3.      http://emedicine.medscape.com/article/117648-overview

4.      http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Diabetes_insipidus

5.      http://www.merckmanuals.com/home/hormonal_and_metabolic_disorders/pituitary_gland_disorders/central_diabetes_insipidus.html