Endocrine Abstracts

Background: Pituitary metastases are a rare occurrence, accounting for just 0.4% of intracranial metastatic tumours and are most often associated with breast and lung malignancies. The vast majority of lesions are asymptomatic and due to the predilection of metastasis to the posterior lobe of the pituitary gland, clinical presentation with anterior pituitary insufficiency is uncommon and rarely reported in literature.

Case summary: A 51-year old male with known epidermal growth factor receptor-positive lung adenocarcinoma was admitted with mild nausea and vomiting secondary to chemotherapy. Five days into admission he developed confusion and biochemistry revealed a new hyponatraemia with a low sodium level of 116 mmol/l. Urine osmolality was elevated and urinary sodium was significantly raised (104 mmol/l). Cortisol was low (119nmol/l) and subsequent short-synacthen test showed an inadequate adrenal response. ACTH was 16ng/l and T4 was low (10.3pmol/l) with a normal TSH. Completion of the pituitary profile demonstrated a low testosterone (< 0.1nmol/l), with inappropriately normal gonadotrophin levels (LH 2.4iu/l, FSH 1.4iu/l) and a low IGF-1 (6.3mol/l). Prolactin was normal. Magnetic resonance imaging showed a pituitary lesion alongside extensive brain metastases. In the context of the biochemical and radiological findings the pituitary lesion was concluded to be of metastatic aetiology. Symptoms and hyponatraemia improved with corticosteroids and subsequent thyroid hormone replacement. The patient commenced second-line chemotherapy and will receive whole-brain irradiation.

Conclusions and Learning points: Most pituitary metastases are diagnosed in patients with known cancer and therefore any biochemical or clinical sign of pituitary gland pathology in this context should prompt further investigation. In this case the presence of an elevated urinary sodium (>100 mmol/l) was a clue to the underlying cause of the hyponatraemia being caused by adrenal insufficiency and hypothyroidism rather than SIADH, a distinction that is crucial for appropriate management.