Curriculum · Metabolic and Endocrine and Diabetes Mellitus
Central versus nephrogenic diabetes insipidus
What it is
Diabetes insipidus is polyuria with a low urine osmolality and a low specific gravity. In central DI the fault is low ADH secretion. In nephrogenic DI, ADH secretion is normal but the tubules cannot respond to ADH; this ADH resistance may follow an ADH receptor mutation, and one source puts the fault in the V2 canals. Both forms appear under euvolemic hypernatremia, where water is lost in the urine and not replaced, next to the osmotic urinary losses of glucosuria and mannitol.
Causes and risk
Central DI may be primary and idiopathic, or secondary to brain lesions such as tumors, hypoxic injury or surgery. Nephrogenic DI follows an ADH receptor mutation, medications, or electrolyte disturbances. The medications named are lithium and demeclocycline, both of which will precipitate nephrogenic DI, and the electrolyte disturbances are hypercalcemia and hypokalemia. Primary polydipsia, which enters the same differential, comes instead from psychiatric diseases such as schizophrenia and obsessive-compulsive disorder, or from lesions in the hypothalamic thirst center.