The following points highlight the two main types of diabetes insipidus. The types are:- 1. Central (Neurogenic) Diabetes Insipidus 2. Nephrogenic Diabetes Insipidus.
Type # 1. Central (Neurogenic) Diabetes Insipidus:
In central diabetes insipidus, the ADH secretion is poor. Pituitary adenomas rarely causes decrease release of ADH, but hypothalamic tumors such as craniopharyngiomas or other primary central nervous system lesions and infiltrative or invasive lesions mostly cause damage to the hypothalamic pituitary nerve tracts resulting in disturbances in the transport of ADH from hypothalamic neurons to neurohypophysis.
These lesions may also damage hypothalamic neurons that synthesise ADH. Familial central diabetes insipidus is an autosomal dominant disease that usually occurs in association with diabetes mellitus, optic atrophy and deafness.
The primary symptoms of central diabetes are persistent polyuria and its companions, thirst and polydipsia. The volume of urine may vary from only a few litres per day to a maximum of 18L/day. Most patients have abrupt onset of polyuria and polydipsia in contrast to the slow onset of polyuria due to impaired renal handling of water.
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They usually show a particular predilection for cold or iced drinks to quench thirst. If access to water is interrupted, hypertonic volume depletion develops; these manifestations may cause mental dullness and progressing to coma with secondary signs of ataxia, hyperthermia and hypotension.
Physiologically the plasma osmolality is greater than 287 m mol/L. Serum sodium levels are also elevated and account for the increases in plasma osmolality. In contrast, patients with primary polydipsia have an aberrant thirst mechanism and ingest water independent of physiological stimuli and often have mild dilutional hyponatremia.
Diabetes insipidus, either central or nephrogenic if starts in childhood may impair renal functions due to dilation of urinary bladder, uretus and renal pelvis.
Causes of Neurogenic Diabetes Insipidus:
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i. Hypophysectomy, Complete or Partial
ii. Survey to remove suprasellar tumors
iii. Idiopathic
iv. Familial
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v. Tumors and Cysts
vi. Histiocytosis
vii. Granulomas
viii. Infections
ix. Interruption of Blood Supply
x. Autoimmune
Type # 2. Nephrogenic Diabetes Insipidus:
This type of disease is caused by renal unresponsiveness to physiologic actions of ADH which is secreted normally. The renal medullary defects as caused by pyelonephritis, polycystic disease or cystic disease may prevent formation of a medullary concentration gradient, and, thus, urine passing through the collecting duct system cannot become concentrated.
Electrolyte disorders like hypokalemia and hypercalcemia reduce urinary concentration capacity. Congenital nephrogenic diabetes is suggested to be X-linked inheritance.
The common picture of this diabetes is volume concentration, hypernatremia and hyperthermia. Mental and physical retardation may occur in some children. Urine excreted is always hypnotic to plasma. In some patients, dilation of urinary tract may progress to hydroureter, hydronephrosis and a urinary capacity of more than 1 litre.
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The most characteristic differences of this diabetes with central diabetes is the absence of thirst and unresponsiveness to administered vasopressin. Renal function is normal as there is no dehydration.
Causes of Nephrogenic Diabetes Insipidius:
i. Chronic renal diseases: Any renal disease that interferes with collecting duct or medullary function, e.g. chronic pyelonephritis.
ii. Hypokalemia
iii. Protein Starvation
iv. Hypercalcemia
v. Sickle cell anaemia
vi. Sjogren’s syndrome
vii. Drugs, e.g. lithium, fluoride, methoxyflurane anesthesia, demeclocycline (Declomycin), colchicine
viii. Congentital defect
ix. Familial