After head injury a patient passes 8 litres of dilute urine per day. Water deprivation fails to concentrate the urine, but desmopressin does. What is the diagnosis?
Answer and explanation
Correct answer: A. Cranial diabetes insipidus
- Step 1: The urine concentrates only when the missing hormone is replaced. Step 2. Response to desmopressin shows the kidney can respond, so ADH production is deficient from the pituitary. Answer: Cranial diabetes insipidus. Why not the others: Nephrogenic disease does not respond to desmopressin. Primary polydipsia concentrates urine with water deprivation. Diabetes mellitus causes glycosuria and hyperglycaemia.
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