Diabetes insipidus is a rare disorder of ADH homeostasis characterized by pathologically high urine output, resulting thirst, and an electrolyte disturbance.
Pathophysiology
A distinction is made between nephrogenic diabetes insipidus (diabetes insipidus renalis) and central diabetes insipidus (diabetes insipidus centralis) [^1]. In nephrogenic diabetes insipidus, ADH levels are normal to elevated, and the condition results from relative renal resistance to ADH. In central diabetes insipidus, ADH levels are subnormal, and the condition results from dysfunction of the hypothalamic-pituitary axis [^1].
Etiology
Diabetes insipidus can have various causes [^2]:
Central diabetes insipidus
Diabetes insipidus centralis results from an excessively low ADH level. Approximately 85 % of ADH secretory capacity must be lost before clinical manifestations of diabetes insipidus centralis develop [^1].
Familial (autosomal dominant inheritance)
Idiopathic
Posttraumatic (Traumatic brain injury or iatrogenic after surgical procedures)
Tumors (e.g., Craniopharyngioma)
Granulomas
Infectious: Meningitis, Encephalitis
Autoimmune
Vascular: Aneurysms, Sheehan syndrome
Nephrogenic diabetes insipidus
Diabetes insipidus renalis results from renal insensitivity to ADH.
Autoimmune
Hypokalemia
Hypercalcemia
Sjögren's syndrome
Medication-induced: Lithium, Demeclocycline, Colchicine
Chronic kidney diseases (e.g., pyelonephritis, amyloidosis, sickle cell anemia, polycystic kidney disease, sarcoidosis)
Diagnosis
The diagnosis can be established based on the following criteria [^1]:
Increased urine production > 250 ml\/h in adults and > 3 ml\/kg\/h in the pediatric population
Normal or elevated serum sodium
Urine osmolality < 200 mOsm\/kg (normally 50-150) or specific gravity < 1.003.
Inability to concentrate urine to > 300 mOsm\/kg despite the presence of clinical signs of dehydration.