Background: Pituitary metastasis (PM) is a rare occurrence in malignancy, associated with poor prognosis. Only 7% of patients are symptomatic. High index of suspicion and prompt investigation are essential. We report a case of PM, highlighting challenges in diagnosis and management.
Case Report: Sixty-six year old male was referred to endocrinology due to headaches and hyponatremia. He had metastatic colorectal carcinoma, treated with bowel, liver and lung resections and chemotherapy. Clinical examination was unremarkable and he was euvolemic. Baseline investigations suggested SIADH (serum sodium (Na) 121 mmol/l, plasma osmolality 253 mmol/kg, urine osmolality 318 mmol/kg and urine sodium 45 mmol/l). CT Head was normal. Further investigation supported provisional diagnosis of adrenal insufficiency (9am cortisol 97nmol/l) and hydrocortisone was added to management with fluid restriction. Bloods later returned with borderline satisfactory cortisol response (471 nmol/l, new assay) on short synacthen test (SST) and normal ACTH (11.1 ng/l). MRI head and CT thorax, abdomen and pelvis (including adrenals) were unremarkable. Hydrocortisone was stopped and patient discharged. Two days later, he presented with symptomatic hyponatremia (Na 122 mmol/l). Hydrocortisone was restarted and Na levels normalised. Anterior pituitary hormone profile revealed panhypopituitarism and MRI Pituitary showed PM (6-7 mm lesion in proximal pituitary stalk). Dexamethasone and levothyroxine was started. MDT review deemed him for palliation only. One month later he passed away.
Conclusion: PM should be considered as a differential for hyponatremia due to adrenal insufficiency in patients with metastatic cancer. Our case highlights the complexities of diagnosing secondary adrenal insufficiency of recent onset as SST may show misleading borderline normal response. High clinical suspicion and early scrutiny with full pituitary hormone profile and imaging can aid in timely diagnosis of PM.