Pituitary Metastasis Presenting With Central Diabetes Insipidus and Panhypopituitarism

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Abstract Background: Metastatic involvement of the pituitary gland and infundibular stalk is rare, accounting for about 2% of all diagnosed pituitary masses. Although primary tumors from almost every organ have been reported, breast and lung cancers are the most common primary tumors to metastasize to the pituitary gland. The clinical presentation varies and can include headache, visual impairment, diabetes insipidus, and panhypopituitarism. The posterior lobe of the pituitary is more susceptible to metastatic involvement than the anterior lobe due to its direct blood supply from the systemic circulation, whereas the anterior lobe is supplied by the hypophyseal portal system. Additionally, the smaller posterior lobe can be destroyed with less metastatic volume, allowing for earlier manifestation of symptoms. Clinical Case: An 81-year-old woman with a history of Stage IIA ER+ IDC of the left breast status post lumpectomy and axillary lymph node dissection in 1999 followed by mastectomy in 2009 due to local recurrence presented with confusion for two weeks. At the time, she had known lung metastases and was on palliative chemotherapy. CT head showed a 1.8 cm and 2.3 cm calvarial lytic lesion in the right occipital bone and at the vertex, respectively. MRI brain/pituitary revealed a well-circumscribed, enhancing suprasellar mass measuring 9 x 10 mm likely involving the pituitary infundibulum and hypothalamus with mass effect on the optic chiasm. Laboratory results were consistent with secondary adrenal insufficiency, central hypothyroidism, and hypogonadotropic hypogonadism. Prolactin was mildly elevated due to stalk effect. The patient also had hypernatremia and inappropriately low urine osmolality, which nearly tripled after administration of desmopressin, confirming central diabetes insipidus. She was subsequently started on hydrocortisone, levothyroxine, and desmopressin. Laboratory Results: Prolactin 30.47 (reference range 4.79-23.3 mIU/mL), IGF-1 88 (17-193 ng/mL), 7am ACTH 3.4 (7.2-63.3 pg/mL), 7am cortisol 0.6 (6.2-29 µg/dL), TSH 3.03 (0.47-6.9 U/L), FT4 0.351 (0.75-2 ng/dL), FSH 0.2 (25.8-134.8 mIU/mL), LH <0.1 (7.7-58.5 mIU/mL), estradiol <5 (5-138 pg/mL); before desmopressin: Na 154 (reference range 135-145 mEq/L), urine osm 162 (50-1,200 mOsm/kg); after desmopressin: Na 143 (reference range 135-145 mEq/L), urine osm 469 (50-1,200 mOsm/kg) Conclusion: While pituitary metastases remain rare, their prevalence is expected to increase due to more sensitive biochemical tests and imaging techniques coupled with advances in cancer therapy that help patients with metastatic disease live longer. Interesting in our case is the patient’s age, which is significantly older than the median age reported in the literature, and her presentation with total anterior and posterior pituitary insufficiency after a prolonged oncologic course marked by progression of disease.