Definition
- Diabetes insipidus (DI) is a syndrome caused by deficiency of ADH, or renal unresponsiveness to it.
- The result is abnormally large volumes of dilute urine, usually due to hypothalamic or posterior pituitary dysfunction.
- Named because the urine is tasteless ("insipidus"), unlike the sweet ("mellitus"), glucose-rich urine of diabetes mellitus.
Clinical Features
- Polyuria: ADH deficiency promotes water diuresis.
- Polydipsia: secondary to the dehydration caused by the polyuria.
- Polyuria and polydipsia are also features of diabetes mellitus; the two are differentiated by urine osmolality.
Classification of Diabetes Insipidus
Types of diabetes insipidus
Type
Nephrogenic
- Basis
- Kidneys fail to respond to ADH; ADH secretion is normal
Neurogenic (central)
- Basis
- Deficiency of ADH secretion