A 60-year-old man comes to the office due to persistent cough for the past several weeks. He reports producing minimal sputum that recently has contained occasional specks of blood. The patient also has anorexia and has lost 7 kg (15.4 lb) over the past 2 months. He has no previous medical conditions and takes no medications. The patient has smoked a pack of cigarettes daily for 40 years and drinks alcohol on social occasions. Temperature is 37.1 C (98.7 F) , blood pressure is 130/80 mm Hg, pulse is 72/min, and respirations are 16/min. On physical examination, respirations are unlabored, and there are occasional wheezes on the left side. The remainder of the examination shows no abnormalities. A chest x-ray reveals a hilar mass with adenopathy on the left side. Laboratory results demonstrate a decreased serum sodium level. Which of the following additional laboratory abnormalities are most likely to be present in this patient?

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Quizplus · Accepted Answer

11ec160b_3b5d_632b_9249_4780ebebc85d_MD0001_00 This patient with a significant smoking history, cough, weight loss, and left-sided hilar lung mass with adenopathy likely has lung cancer. He also has new hyponatremia. Certain tumors (eg, small cell lung carcinoma, head and neck cancer) can ectopically produce antidiuretic hormone (ADH), which can lead to hyponatremia due to the syndrome of inappropriate secretion of ADH (SIADH). ADH secretion from the posterior pituitary is normally stimulated by high serum osmolality (eg, water deprivation) or low extracellular volume (eg, dehydration). Increased ADH leads to water reabsorption in the renal collecting ducts, lowering serum osmolality and suppressing further ADH secretion. However, in SIADH, excessive uncontrolled ADH secretion occurs, causing the following changes: Patients with SIADH are typically euvolemic (eg, absent jugular venous distension, normotension). Initially, increased reabsorption of water in SIADH may cause a transient volume expansion; however, subsequent natriuresis (sodium and water excretion) restores the extracellular volume to normal. (Choice A) High serum osmolality and high urine osmolality (concentrated urine) can be seen in severe hyperglycemia (eg, diabetic ketoacidosis). High urine osmolality and polyuria results from increased glucose excretion in the urine (osmotic diuresis); dilutional hyponatremia can also occur due to the glucose-driven osmotic pull of water into the extracellular space. (Choice B) High serum osmolality with low urine osmolality (dilute urine) can be seen in diabetes insipidus, a condition characterized by polyuria and excessive urinary water losses. However, diabetes insipidus is associated with a high or high/normal serum sodium, rather than this patient's hyponatremia. This patient also has no history of polyuria. (Choice E) Low serum osmolality and low urine osmolality are characteristic of primary polydipsia, a disorder caused by excessive water intake. This disorder can be due to CNS disorders or psychotropic medications and is also associated with hyponatremia (ie, hypotonic hyponatremia). However, ADH levels are low, rather than increased, and patients often have polyuria. This patient has no history of excessive water intake or polyuria. Educational objective: Ectopic production of antidiuretic hormone (ADH) from malignancy can lead to the syndrome of inappropriate ADH secretion, a condition of impaired urinary water excretion. This condition manifests with low serum osmolality, hyponatremia, high urine osmolality, and high urine sodium. __________ References: Syndrome of inappropriate antidiuretic hormone secretion: Revisiting a classical endocrine disorder. (http://www.ncbi.nlm.nih.gov/pubmed/22029026)

A 60-Year-Old Man Comes to the Office Due to Persistent