Metastatic lung adenocarcinoma presenting with central diabetes insipidus

What happened, in summary

This 50-year-old Iranian man came to the hospital with 20 days of polyuria and polydipsia. Initial tests showed low urine specific gravity and high serum sodium, and he was referred with suspected diabetes insipidus. Intranasal desmopressin was started at 1 puff daily, then increased to 2 puffs daily after 3 days, which improved his symptoms. The pattern suggested a central cause, meaning the problem was not simply excess fluid intake or kidney-related water loss. Brain MRI showed a normal pituitary gland and surrounding sellar structures, but hyperintense lesions were present in the right rectus gyrus and left occipital lobe. Imaging also showed multiple metastatic bone lesions in the cervical spine. A more detailed history then revealed about 10 kg of unintentional weight loss over 3 months. Chest CT showed consolidation with air bronchograms, patchy ground-glass opacities, and multiple nodules in the right upper lobe, along with bilateral mediastinal and hilar lymphadenopathy and bilateral pleural effusion. Transbronchial lung biopsy showed atypical epithelial cells with large, pleomorphic, hyperchromatic nuclei, consistent with lung adenocarcinoma. Immunohistochemistry was weakly positive for TTF-1, Napsin A, and p63, while CK5/6 was negative. Molecular testing for driver mutations could not be performed because of financial constraints. He was admitted to hemato-oncology and began systemic platinum-based chemotherapy, given on day 1 and day 8 after admission, while desmopressin continued to address the diabetes insipidus symptoms. Despite treatment, his condition deteriorated, and he died shortly after the second chemotherapy cycle. The case highlights lung adenocarcinoma presenting through central diabetes insipidus without visible pituitary metastasis.