Hyponatremia Associated with Unilateral Hand Weakness and Numbness: A Case Report

CONTEXT: The key clinical features in this case are to make the diagnosis apical lung cancer (Pancoast tumor) in a patient with brachial plexopathy and to recognize the association between syndrome of inappropriate secretion of antidiuretic hormone (SIADH) as a paraneoplastic syndrome and non-small cell lung cancer (NSCLC). CASE REPORT: We herein describe a rare case of NSCLC presented as pancoast tumor complicated by brachial plexopathy and associated with SIADH as a paraneoplastic phenomena. There were no renal insufficiency, congestive cardiac failure, liver insufficiency, volume depletion, diuretic use, hypoadrenalism, and hypothyroidism in our patient. Furthermore, the findings of serum hyponatraemia and hypo-osmolality associated with an inappropriate high urinary osmolality indicate that the SIADH was present in our patient due to the NSCLC. CONCLUSION: Our case also emphasizes that early recognition and appropriate applied management may significantly improve symptoms and prevent complications of hyponatremia which may enhance quality of life in patients with paraneoplastic SIADH.