Lung nodules do not normally cause hyponatremia. However, if the lung nodule is caused by a malignant tumor of the lung, hyponatremia may occur. Lung nodules are generally defined as focal, round-like shadows of the lungs that appear on imaging to be less than 30 mm in diameter. If the lung nodule is small, it has less impact on the lung tissue and usually does not cause significant clinical symptoms. When the lung nodules are larger or widely distributed, symptoms such as cough, chest tightness, and shortness of breath may be present, and generally the lung nodules do not cause hyponatremia. However, when lung nodules are caused by malignant tumors in the lungs, they may lead to hyponatremia. A common reason why lung cancer patients are prone to hyponatremia is the syndrome of inappropriate secretion of antidiuretic hormone. When antidiuretic hormone is overproduced, water excretion is impaired, resulting in hyponatremia. It is recommended that patients with symptoms of hyponatremia or lung nodules should seek medical treatment in time, complete the examination, clarify the cause of the disease, and standardize the treatment under the guidance of doctors.