Unusual presentation of lung carcinoma with pituitary metastasis: a challenging diagnosis and sodium management dilemmas.

When patients present with pituitary mass and diabetes insipidus (DI), pituitary metastasis should be considered as an initial differential diagnosis. DI caused by pituitary adenoma is rare and is typically a late finding.DI can present as severe hyponatremia when coexisting with adrenal insufficiency.Cortisol can directly inhibit endogenous antidiuretic hormone (ADH) secretion. Patients with adrenocorticotropic hormone deficiency will have increased tonic ADH activity and subsequently reduced capacity for free-water excretion. However, when on steroid therapy, patients should be monitored for possible DI because steroids can restore free-water excretion.A substantial change in serum sodium after desmopressin treatment should eliminate the possibility of desmopressin overdose or coexistence of DI and syndrome of inappropriate ADH secretion in patients with lung cancer. Therefore, frequent monitoring of serum sodium concentrations is crucial.