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Question 32#

A 55-year-old woman with a history of severe depression and radical mastectomy for carcinoma of the breast 1 year previously develops polyuria, nocturia, and excessive thirst.

Laboratory values are as follows:

Which of the following is the most likely diagnosis?

a. Psychogenic polydipsia
b. Renal glycosuria
c. Hypercalciuria
d. Diabetes insipidus
e. Inappropriate antidiuretic hormone syndrome

Correct Answer is D


Metastatic tumors rarely cause diabetes insipidus, but of the tumors that cause it, carcinoma of the breast is by far the most common. In this patient, the diagnosis of diabetes insipidus is suggested by hypernatremia and low-urine osmolality. To distinguish between central (ADH deficiency) and nephrogenic (peripheral resistance to ADH action) diabetes insipidus, vasopressin (ADH by another name) is administered. If the urine osmolality rises and the urine output falls, the diagnosis is central DI. There will be little response to vasopressin in nephrogenic DI. Psychogenic polydipsia is an unlikely diagnosis since serum sodium is usually mildly reduced in this condition. Renal glycosuria would be expected to induce higher-urine osmolality than this patient has because of the osmotic effect of glucose. While nephrocalcinosis secondary to hyper-calcemia may produce polyuria, hypercalciuria does not. Finally, the findings in inappropriate antidiuretic hormone syndrome are the opposite of those observed in diabetes insipidus and thus are incompatible with the clinical picture in this patient.