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Introduction: The association of inappropriate anti-diuretic hormone secretion syndrome with malignancy was first described in two patients with bronchogenic carcinoma in 1957. Inappropriate ADH syndrome is a paraneoplastic syndrome, which is mainly seen in patients with small cell lung cancer. However, it might rarely be seen in cases with non-small cell lung cancer and be the first sign of the disease.
Case Presentation: A 74-year-old male patient admitted to our clinic with a one-week history of muscle weakness, fatigue, anorexia and dyspnea. In his past medical history, he had smoking history of 50 pack-years, and diagnoses of COPD, coronary artery disease, type 2 diabetes mellitus, and cured non-hodgkin lymphoma 10 years ago. Physical examination revealed coarse crackles in the bilateral lung bases. Laboratory analysis revealed a normal whole blood count. Serum sodium: 116 mEq/dL (N: 136-146), serum osmolality: 260 mOsm/kg H2O (N:280-301), serum creatinine: 0.44 mg/dL (N: 0.67-1.17), urine osmolality: 225 mOsm/kg H2O (N: 300-900), urine sodium: 24.6 mEq/L (N>20), cortisol: 9.89 µg/dL (N: 6.7-22.6), TSH:1.086 uIU/mL (N: 0.38-5.33). The patient was utilized as inappropriate ADH syndrome, and fluid restriction and sodium chloride were implemented. The patient was not taking any medication that can cause hyponatremia. After an abnormal chest radiography revealing left hilar enlargement, the patient underwent a computed tomography of thorax. There were a left hilar mass lesion invading the mediastinum, mediastinal and left hilar lymphadenopathies, and metastatic pulmonary nodules on both lungs. The SUVmax of the left hilar mass lesion was 11.3 on PET-CT. Additionally, there were increased uptake values consistent with metastatic disease in mediastinal lymph nodes, metastatic pulmonary nodules in both lungs, the subcutaneous nodule palpable on the base of left hemithorax, spleen and multiple bones. Bronchoscopy was performed. Pathological examination of forceps biopsies obtained from the left upper lobe carina was compatible with squamous cell carcinoma. Systemic chemotherapy was planned. However, the patient refused to receive chemotherapy and died 3 months after the diagnosis.
Conclusion: It should be kept in mind that as a paraneoplastic syndrome, inappropriate ADH syndrome may be seen in a patient with non-small cell lung cancer.