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Picture quiz: Diabetes insipidus in a woman with breast cancer
Scholarly Journal
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A 43 year old woman was admitted with a two week history of intermittent headache and a three month history of progressive malaise and headache. She had a history of node positive lobular breast cancer, treated with right mastectomy, chemotherapy, and tamoxifen eight years before. Magnetic resonance imaging of the brain showed a large suprasellar mass (figure). Visual acuity was normal and visual fields were full. Baseline and dynamic endocrine investigation confirmed anterior pituitary dysfunction affecting the glucocorticoid (morning cortisol low at 21 nmol/l, with adequate adrenal response to synthacten); growth hormone (no response to growth hormone after giving glucagon); and thyroid axis (inappropriately normal thyroid stimulating hormone at 2.76 mU/l with reduced thyroxine at 8.00 pmol/l). Prolactin concentrations were within the normal range at 132 mU/l. She was treated with replacement hydrocortisone and thyroxine. A few weeks later she was admitted with polyuria and polydipsia. A paired serum concentration of 308 mmol/kg with urine concentration of 158 mmol/kg was in keeping with the diagnosis of diabetes insipidus. She responded to treatment with desmopressin. Further investigations showed liver and pulmonary metastases. Questions What is the most likely cause of the suprasellar mass and panhypopituitarism in this woman and why? What is the differential diagnosis of a suprasellar mass? Give possible explanation for the delayed onset of diabetes insipidus? Answers The most likely cause of the lesion in the pituitary region is metastases from carcinoma of the breast. The presence of diabetes insipidus supports metastases rather than a pituitary adenoma in which diabetes insipidus is rare, occurring in only 1% of patients. 1 In addition to primary pituitary adenomas, other conditions can present as a lesion in the pituitary area (box). Most of these conditions are rare. (3) The ability of the kidneys to excrete a free water load is impaired...