Cause of Nephrogenic Diabetes Insipidus

Nephrogenic diabetes insipidus occurs due to:

Correct Answer: Receptor of ADH does not respond

Nephrogenic diabetes insipidus occurs when the kidneys do not respond normally to ADH (antidiuretic hormone) despite ADH being present in normal or elevated levels. The ADH receptor (V2 receptor) in the collecting duct does not function properly.

Types of Diabetes Insipidus (DI)

• Neurogenic / Central DI: Deficiency of ADH production from posterior pituitary (e.g., head trauma, pituitary tumour)
• Nephrogenic DI: ADH is produced normally, but kidney's V2 receptors or aquaporin-2 channels fail to respond → kidneys cannot concentrate urine

Comparison: Both Types of DI Share the Same Symptoms

• Polyuria (excess dilute urine output)
• Polydipsia (excessive thirst)
• Normal blood glucose (unlike Diabetes Mellitus)
• Lower specific gravity of urine

How to Distinguish Central from Nephrogenic DI

Desmopressin (synthetic ADH) test:

• Central DI: Responds to desmopressin → urine concentrates
• Nephrogenic DI: Does NOT respond to desmopressin (receptor is defective)

Compare with Diabetes Mellitus

Both DI types have polyuria, but in Diabetes Mellitus there is hyperglycemia & glycosuria (high specific gravity of urine), which is absent in DI.