Pituitary macroadenoma: A case of balanced deficiencies

Introduction: We present a patient with a non-functional pituitary macroadenoma who developed diabetes insipidus after initiation of thyroid hormone and cortisol replacement for central hypothyroidism and adrenal insufficiency. Case description: A 61-year-old man with a history of a 1.7cm non-functional pituitary macroadenoma that was stable over a five-year period was found to have an interval growth of 2.1cm on annual follow-up. He was in a good state of health, but laboratory findings revealed central hypothyroidism and central adrenal insufficiency. He was started on glucocorticoid and thyroid hormone replacement with subsequent development of diabetes insipidus. A follow-up MRI demonstrated apoplexy with decrease in tumor size. Pituitary surgery was cancelled. Conclusion: Subclinical apoplexy may occur in a pituitary macroadenoma with pituitary hormone deficiency as the only indication of an occult process. Treating underlying glucocorticoid or thyroid deficiency may unmask diabetes insipidus. Alternative diagnosis should be investigated in a patient with a pituitary macroadenoma who suddenly develops diabetes insipidus.