A 72-year-old man comes to the office after several days of mild headache and lethargy. He has also had weakness, chronic cough, and decreased appetite. He drinks 2 or 3 beers each weekend and has a 40-pack-year smoking history. Temperature is 37 C (98.6 F), blood pressure is 120/84 mm Hg, pulse is 78/min, and respirations are 24/min. Lung examination shows mildly prolonged expiration with end-expiratory wheezes. Laboratory results are as follows: Chest x-ray reveals overinflated lung fields and a 2.5-cm left hilar mass. Biopsy of the mass would most likely show which of the following?

Question

A 72-year-old man comes to the office after several days of mild headache and lethargy.  He has also had weakness, chronic cough, and decreased appetite.  He drinks 2 or 3 beers each weekend and has a 40-pack-year smoking history.  Temperature is 37 C (98.6 F), blood pressure is 120/84 mm Hg, pulse is 78/min, and respirations are 24/min.  Lung examination shows mildly prolonged expiration with end-expiratory wheezes.  Laboratory results are as follows:  Chest x-ray reveals overinflated lung fields and a 2.5-cm left hilar mass.  Biopsy of the mass would most likely show which of the following?

Quizplus · Accepted Answer

11ec160b_3a1e_c908_9249_937ae0a4f35e_MD0001_00 This patient's hyponatremia is most likely due to syndrome of inappropriate antidiuretic hormone (SIADH), which is one of several paraneoplastic syndromes that may occur in patients with small cell lung cancer (SCLC). Presenting symptoms of SIADH are often vague (eg, lethargy), but untreated SIADH can lead to significant hyponatremia causing seizures or coma. Physical examination should reveal euvolemia, and laboratory results should demonstrate decreased serum osmolality consistent with true (hypotonic) hyponatremia. An essential characteristic of SIADH is urine osmolality >100 mOsm/kg H₂O, which reflects inability of the kidneys to produce adequately dilute urine to remove excess free water from the body (due to inappropriately high levels of ADH). SIADH may be caused by excessive release of ADH from the posterior pituitary (eg, central nervous system disorder, medication adverse effect) or ectopic secretion of ADH. SCLC, a neuroendocrine tumor that typically presents as a hilar mass in patients with a significant smoking history, is the most common cause of ectopic secretion of ADH. (Choice A) Carcinoids are rare neuroendocrine tumors that typically occur in the digestive tract or lungs. They may lead to carcinoid syndrome (eg, flushing, diarrhea, bronchoconstriction), which is a paraneoplastic syndrome caused by secretion of serotonin, histamine, and kinins. Carcinoids may rarely cause SIADH, but SCLC is more likely in this patient with a hilar mass and significant smoking history. (Choices B, D, and F) Lung adenocarcinoma may cause paraneoplastic hypertrophic osteoarthropathy, and squamous cell carcinoma can lead to paraneoplastic hypercalcemia (due to tumor secretion of parathyroid hormone-related protein). Mesothelioma is a rare malignancy derived from the mesothelial lining of the thoracic cavity and has been associated with a variety of paraneoplastic syndromes (eg, peripheral neuropathy, migratory thrombophlebitis). SIADH due to any of these malignancies would be unusual. (Choice C) Paraneoplastic syndromes associated with lymphoma include hypercalcemia due to overproduction of 1,25-dihydroxyvitamin D and cerebellar degeneration. SIADH would be unusual. Educational objective: Small cell lung cancer is a neuroendocrine malignancy associated with several paraneoplastic syndromes. It is the most common cause of syndrome of inappropriate antidiuretic hormone (SIADH) due to ectopic secretion of antidiuretic hormone. SIADH is characterized by hyponatremia, decreased serum osmolality, and urine osmolality >100 mOsm/kg H₂O. __________ References: Paraneoplastic syndromes associated with lung cancer. (http://www.ncbi.nlm.nih.gov/pubmed/25114839) Lung cancer-induced paraneoplastic syndromes. (http://www.ncbi.nlm.nih.gov/pubmed/21577115)

A 72-Year-Old Man Comes to the Office After Several Days