A 55-year-old woman who has a history of severe depression and who had radical mastectomy for carcinoma of the breast 1 year previously develops polyuria, nocturia, and excessive thirst. Laboratory values are as follows: (AIIMS Nov 2011)
Serum electrolytes: Na− 149 meq/L; K− 3.6 meq/L
Serum calcium: 9.5 mg/dL
Blood glucose: 110 mg/dL
Blood urea nitrogen: 30 mg/dL
Urine osmolality: 150 mOsm/kg
The most likely diagnosis is
|B||Inappropriate antidiuretic hormone syndrome|
1). Metastatic tumors rarely cause diabetes insipidus, but of the tumors that may cause it, carcinoma of the breast is by far the most common.
2). In this patient, the diagnosis of diabetes insipidus is suggested by hypernatremia and low urine osmolality.
3). Psychogenic polydipsia is an unlikely diagnosis since serum sodium is usually mildly reduced in this condition.
4). Renal glycosuria would be expected to induce a higher urine osmolality than this patient has because of the osmotic effect of glucose.
5). While nephrocalcinosis secondary to hypercalcemia may produce polyuria, hypercalciuria does not.
6). Finally, the findings of inappropriate antidiuretic hormone syndrome are the opposite of those observed in diabetes insipidus and thus are incompatible with the clinical picture in this patient.