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Answers on p 251.
A 24 year old woman presented with a three week history of weight loss, thirst, polyuria, sweating, and nausea. For three days before admission she had abdominal pains and vomiting after meals. Past medical history included acromegaly treated by trans-sphenoidal resection of a pituitary macroadenoma at the age of 19 years. Postoperatively, she did not have diabetes insipidus; however, she developed anterior hypopituitarism replaced with hydrocortisone 10 mg twice daily, thyroxine 100 μg daily, and ethinyloestradiol and desogestrel for three weeks every month. She also had persistent postoperative acromegaly that was well controlled with bromocriptine 7.5 mg daily. She had not received postoperative radiotherapy.
Clinical examination revealed postural hypotension with supine blood pressure 130/70 mm Hg and standing blood pressure 85/45 mm Hg. She was in sinus rhythm with a heart rate of 94 beats/min. Visual acuity was 6/24 in the right eye and 6/5 in the left eye. Visual field examination showed temporal hemianopia in the right eye and full field in the left eye. Fundoscopy showed bilateral optic atrophy, right more than left, likely the result of her pituitary macroadenoma. She had mild periumbilical tenderness to deep palpation without any guarding or rigidity. Bowel sounds were present. The rest of the clinical examination was normal.
Investigations showed normal electrolytes, urea, creatinine, glucose 3.2 mmol/l, serum osmolality 297 mmol/kg water (reference range 288–298) and urine osmolality 178 mmol/kg water. Corrected serum calcium was raised at 3.01 mmol/l (reference range 2.15–2.55 mmol/l) with parathyroid hormone (PTH) <0.08 pmol/l indicating non-parathyroid cause of hypercalcaemia. Insulin like growth factor 1 was normal at 17 nmol/l (reference range 15–64). She was rehydrated with intravenous isotonic saline and her dose of hydrocortisone temporarily increased but her hypercalcaemia persisted.
A water deprivation test was normal, with urine osmolality 1032 mmol/kg water and serum osmolality 287 mmol/kg water after eight hours of water deprivation. Results of thyroid function tests were available at this stage showing free thyroxine 111 pmol/l with thyroid stimulating hormone <0.03 mU/l. Her thyroxine replacement was stopped and a 99mtechnetium (99mTc) pertechnate thyroid uptake scan was done after seven days (fig 1). Thyroid stimulating hormone receptor autoantibodies (TSHRAb) were positive at 75 U/l (reference range <10 U/l). Magnetic resonance imaging revealed an enlarged empty pituitary fossa with a thin rim of pituitary tissue in the periphery.
What are the possible causes of thirst and polyuria in this woman?
What are the possible causes of hypercalcaemia?
What is the cause of her thyrotoxicosis?
Is there an association between acromegaly and thyrotoxicosis?