CASE STUDY
LR is a 73-year-old gentlemen who presented with two months of polydipsia and polyuria. His medical history included renal cell carcinoma in remission and he was a current smoker. Examination showed normal visual fields.
A water deprivation test was performed, urine osmolality increased by 20% after desmopressin was given suggestive of partial central diabetes insipidus. He was commenced on desmopressin. Initial pituitary function assessment revealed hypogonadotrophic hypogonadism. Within the next 4 weeks, he developed central hypothyroidism and secondary adrenal insufficiency and was commenced on thyroxine and hydrocortisone.
MRI showed a pituitary mass compressing the optic chiasm, other cerebral lesions were also present suspicious for metastases. CT chest showed a left upper lobe lung mass. Histology from the lung biopsy revealed lung adenocarcinoma. This histology in the context of the rapid progression to panhypopituitarism was highly suggestive of metastatic non-small cell lung carcinoma.
LR received radiotherapy to the pituitary metastases and chemotherapy. Despite a complete metabolic response on staging, he remains on pituitary hormone replacement.
DISCUSSION
Pituitary metastases are rare, neoplasms from almost every tissue have been reported to metastasise to the pituitary with breast and lung accounting for two-thirds of pituitary metastases.
Diabetes insipidus is the most common clinical presentation of symptomatic pituitary metastases. This highlights a predominance of metastasis to the posterior lobe, likely from direct haematogenous spread through the inferior hypophyseal artery. Pituitary insufficiency may be apparent at presentation or present insidiously and patients should be alert to symptoms and be regularly screened.
Water-deprivation test was used to diagnose diabetes insipidus. Copeptin is useful as an initial test to diagnose or exclude central diabetes insipidus. However, it is not widely available and lead time can delay diagnosis. Pituitary metastases should be a considered as a rare differential diagnosis especially in patients presenting with diabetes insipidus.