A 67-year-old man is evaluated in the emergency department with a 3-day history of weakness and nausea and a 2-week history of difficulty swallowing. He has lost 22.7 kg (50 lb) during the past year. He has no other symptoms. History is significant for a 30-pack-year history of smoking. He quit smoking 4 years ago. He takes no medications.
On physical examination, vital signs are normal. Lung examination reveals decreased tactile fremitus above the lower portion of the right lung as well as dullness to percussion and decreased breath sounds. His neurologic examination is normal.
Laboratory studies reveal a serum sodium concentration of 127 mEq/L (127 mmol/L).
A chest CT scan is shown.
Which of the following is the most likely diagnosis?
A. Adenocarcinoma of the lung
B. Malignant pleural mesothelioma
C. Small cell lung cancer
D. Squamous cell carcinoma of the lung
Answer and critique
The correct answer is C. Small cell lung cancer. This item is Question 14 in MKSAP 18's Pulmonary and Critical Care Medicine section.
The most likely diagnosis is small cell lung cancer (SCLC). SCLC is a neuroendocrine tumor that accounts for approximately 15% of all lung cancers and occurs predominantly in smokers.
This patient has signs and symptoms of hyponatremia and chest CT scan shows a large mediastinal right hilar mass and right-lower-lobe mass.
Imaging studies in SCLC commonly demonstrate a large hilar mass with bulky mediastinal lymphadenopathy; some patients may not have an obvious primary lesion. Signs and symptoms include cough, dyspnea, weight loss, and debility. Less commonly SCLC can present with endocrinologic or neurologic paraneoplastic syndromes. The syndrome of inappropriate antidiuretic hormone secretion (SIADH) due to ectopic production of antidiuretic hormone (ADH) is most often due to a SCLC and is rarely seen with other lung tumors. It occurs in approximately 10% of patients and results in hyponatremia. The severity of symptoms is related to the degree of hyponatremia and rapidity of the decrease. They may include anorexia, nausea, and vomiting, but if the decrease is rapid, cerebral edema can occur and may result in irritability, restlessness, personality changes, confusion, coma, seizures, and respiratory arrest. SCLC is more aggressive than non-small cell lung cancer (NSCLC), is usually already disseminated at presentation, and requires prompt treatment; however, it is often initially more sensitive to chemotherapy and radiotherapy but typically relapses and becomes resistant to further treatment. Staging should not delay treatment.
NSCLC accounts for 80% of lung cancers, of which adenocarcinoma is the most common type, followed by squamous cell. Although NSCLC is in the differential diagnosis for this patient, hyponatremia and a large mediastinal mass are most consistent with SCLC.
Malignant pleural mesothelioma typically presents as a recurrent exudative pleural effusion with pleural thickening in a patient with exposure to asbestos. This patient did not present with a pleural effusion, which makes this diagnosis less likely.
- Typical imaging findings in patients with small cell lung cancer (SCLC) include a large mediastinal mass; hyponatremia due to ectopic production of antidiuretic hormone is most often due to SCLC and is rarely seen with other lung tumors.