An 80-year-old man was referred to the endocrinology clinic for headache, thirst, and polyuria of 4 months duration. He was known to have hypertension, diverticulosis, and vitamin B12 deficiency. He drank at least 5 L of fluids per day. He also lost 6 kg of weight. He had no other systemic or alarming symptoms.
On examination, he had normal visual fields and absence of cranial nerve palsy. He weighed 83.9 kg, and his body mass index was 28.4 kg/m. Clinical examination was unremarkable, with no features suggestive of acromegaly, Cushing's, or any other endocrinopathies.
Results of baseline investigations were as follows: sodium of 147 mEq/L, plasma osmolality of 301 mosm/kg, prolactin of 1062 mU/L, and normal levels of other pituitary hormones.
The water deprivation test showed results consistent with cranial diabetes insipidus. At baseline, his urine osmolality was 65 mosm/kg; after 2 h of water deprivation, it was 319 mosm/kg; and after subcutaneous administration of desmopressin, it increased to 416 mosm/kg. He was started with desmopressin and demonstrated good therapeutic response.
MRI of the pituitary gland showed a 10-mm mixed cystic/soft tissue mass lesion filling the posterior aspect of the pituitary sella, with infiltration of the pituitary stalk (Figure 2). He continued to experience headache. Full-brain MRI confirmed the presence of a small nodule in each frontal lobe in addition to the pituitary mass lesion, likely metastatic deposits.
Computed tomography (CT) of the chest, abdomen, and pelvis showed a central tumor of the right lung (CT stage tbl4), prominent para-aortic and left hilar lymph nodes, and metastatic deposit in tbl11.
His general condition deteriorated very quickly, so he was not fit for palliative chemotherapy. He was referred to the palliative care team for symptom management. He died within 1 month of his diagnosis.