Lung tumors (primary and metastatic) US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Lung tumors (primary and metastatic). These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Lung tumors (primary and metastatic) US Medical PG Question 1: A 61-year-old man comes to the physician because of a 2-month history of a cough productive of clear mucoid sputum. He has smoked one pack of cigarettes daily for 33 years. Physical examination shows no abnormalities. Chest x-ray shows a 2-cm solid nodule in the periphery of the lower left lobe. A bronchial biopsy of the mass shows numerous mucin-filled epithelial cells lining the alveolar basement membrane. The cells have prominent nucleoli, coarse chromatin, and some cells have multiple nuclei. Which of the following is the most likely diagnosis?
- A. Endobronchial tuberculosis
- B. Pulmonary hamartoma
- C. Small cell carcinoma
- D. Carcinoid tumor
- E. Adenocarcinoma in situ (Correct Answer)
Lung tumors (primary and metastatic) Explanation: ***Adenocarcinoma in situ***
- The presence of **mucin-filled epithelial cells** lining the **alveolar basement membrane** (**lepidic growth pattern**) is characteristic of adenocarcinoma in situ.
- **Prominent nucleoli**, **coarse chromatin**, and **multinucleated cells** suggest malignancy, and the nodule's peripheral location is typical for adenocarcinomas.
*Endobronchial tuberculosis*
- While it can cause a productive cough and lung nodules, the biopsy findings of **mucin-filled epithelial cells** and specific cytological features of malignancy are inconsistent with tuberculosis.
- Tuberculosis usually shows **granulomas**, **caseation necrosis**, or acid-fast bacilli on biopsy.
*Pulmonary hamartoma*
- A hamartoma is a **benign tumor** composed of disorganized mature tissues, typically containing **cartilage**, fat, and connective tissue.
- It would not show the distinct **mucin-filled epithelial cells** or the malignant cytological features described.
*Small cell carcinoma*
- Small cell carcinoma typically presents as a **central mass** and is characterized by small, **undifferentiated cells** with scant cytoplasm and high nuclear-to-cytoplasmic ratio.
- It does not exhibit the **mucin production** or the lepidic growth pattern seen in this case.
*Carcinoid tumor*
- Carcinoid tumors are **neuroendocrine tumors** that typically display nests or cords of uniform, small cells with "salt-and-pepper" chromatin.
- They are usually located centrally and do not show the **mucin-filled epithelial cells** or the aggressive cytological features described.
Lung tumors (primary and metastatic) US Medical PG Question 2: A 65-year-old man with a 40-pack-year smoking history presents with hemoptysis and a persistent cough. Chest CT shows a 3.5 cm centrally located mass in the right main bronchus. Positron emission tomography confirms a malignant nodule. Bronchoscopy with transbronchial biopsy is performed and a specimen sample of the nodule is sent for frozen section analysis. The tissue sample is most likely to show which of the following tumor types?
- A. Carcinoid tumor
- B. Metastasis of colorectal cancer
- C. Small cell lung carcinoma
- D. Large cell carcinoma
- E. Squamous cell carcinoma (Correct Answer)
Lung tumors (primary and metastatic) Explanation: ***Squamous cell carcinoma***
- This is the most likely diagnosis given the **central location** in the main bronchus, **heavy smoking history**, and presentation with **hemoptysis**.
- **Squamous cell carcinoma** accounts for 25-30% of lung cancers and characteristically arises in **central/proximal airways**, making it readily accessible by **bronchoscopy**.
- Histologically, it shows **keratin pearls** and **intercellular bridges** on biopsy.
- The **central endobronchial location** and ability to obtain tissue via transbronchial biopsy strongly favor squamous cell over peripheral tumors.
*Carcinoid tumor*
- **Carcinoid tumors** are **neuroendocrine tumors** that can present as central endobronchial masses and cause hemoptysis.
- However, they are typically **slow-growing** with more indolent presentation, and PET scans show **variable uptake** (often less intense than aggressive carcinomas).
- They represent only **1-2% of lung tumors** and occur more commonly in **younger, non-smoking patients**.
*Metastasis of colorectal cancer*
- While lung is a common site for **colorectal metastases**, these typically present as **multiple peripheral nodules** rather than a solitary central endobronchial mass.
- The clinical presentation strongly suggests **primary lung cancer** rather than metastatic disease.
- Without history of colorectal cancer, this is unlikely.
*Small cell lung carcinoma*
- **Small cell lung carcinoma** (SCLC) represents 15% of lung cancers and typically presents as a **large central mass** with early mediastinal involvement.
- However, SCLC is usually **too extensive at presentation** for transbronchial biopsy alone and often requires mediastinoscopy or CT-guided biopsy.
- Histology shows **small cells with scant cytoplasm**, **salt-and-pepper chromatin**, and **oat-cell morphology**.
- While possible, the single accessible endobronchial mass is more characteristic of squamous cell.
*Large cell carcinoma*
- **Large cell carcinoma** is a **diagnosis of exclusion** made when tumors lack features of adenocarcinoma, squamous cell, or small cell differentiation.
- It typically presents as **large peripheral masses** rather than central endobronchial lesions.
- It represents only **10% of lung cancers** and is less common than squamous cell carcinoma in this clinical scenario.
Lung tumors (primary and metastatic) US Medical PG Question 3: A 63-year-old male is accompanied by his wife to his primary care doctor complaining of shortness of breath. He reports a seven-month history of progressively worsening dyspnea and a dry non-productive cough. He has also lost 15 pounds over the same time despite no change in diet. Additionally, over the past week, his wife has noticed that the patient appears confused and disoriented. His past medical history is notable for stable angina, hypertension, hyperlipidemia, and diabetes mellitus. He currently takes aspirin, metoprolol, lisinopril, atorvastatin, metformin, and glyburide. He has smoked 1 pack of cigarettes per day for 30 years and previously worked as a mechanic at a shipyard. Physical examination reveals no wheezes, rales, or rhonchi with slightly decreased aeration in the left lower lung field. Mucus membranes are moist with normal skin turgor and capillary refill. Laboratory analysis reveals the following:
Na 121 mEq/L
K 3.4 mEq/L
Cl 96 mEq/L
HCO3 23 mEq/L
Cr 1.1 mg/dl
BUN 17 mg/dl
A biopsy of the responsible lesions will most likely demonstrate which of the following findings?
- A. Anaplastic pleomorphic giant cells
- B. Pleomorphic cells arising from the alveolar lining with disruption of the alveolar architecture
- C. Sheets of large pleomorphic cells containing keratin and intercellular bridges
- D. Undifferentiated small round blue cells (Correct Answer)
- E. Sheets of epithelial cells with papillary fragments, necrosis, and psammoma bodies
Lung tumors (primary and metastatic) Explanation: ***Undifferentiated small round blue cells***
- The patient's history of heavy smoking, shipyard work (exposure to **asbestos**), progressive dyspnea, weight loss, and hyponatremia point towards **small cell lung carcinoma (SCLC)** with possible paraneoplastic **SIADH** causing confusion.
- **SCLC** is characterized histologically by sheets of **small, round, blue cells** with scant cytoplasm, fine chromatin, and absent or inconspicuous nucleoli.
*Anaplastic pleomorphic giant cells*
- This description is more consistent with **large cell carcinoma**, an undifferentiated lung cancer that lacks the specific features of adenocarcinoma, squamous cell carcinoma, or small cell carcinoma.
- Large cell carcinoma does not typically present with the same paraneoplastic syndromes (like SIADH) as SCLC, nor the characteristic "small blue cell" morphology.
*Pleomorphic cells arising from the alveolar lining with disruption of the alveolar architecture*
- This description suggests **adenocarcinoma**, which typically arises from the **glandular cells** of the lung and may disrupt normal alveolar structures.
- While adenocarcinoma can cause dyspnea and weight loss, it is less strongly associated with heavy smoking than SCLC and does not commonly present with **SIADH** and confusion in this manner.
*Sheets of large pleomorphic cells containing keratin and intercellular bridges*
- This biopsy finding is characteristic of **squamous cell carcinoma**, which is often associated with a strong smoking history and can be centrally located.
- However, squamous cell carcinoma less frequently leads to paraneoplastic SIADH, and the classic description for SCLC is "small blue cells," not large pleomorphic cells with keratin.
*Sheets of epithelial cells with papillary fragments, necrosis, and psammoma bodies*
- This pathology description is included as a distractor, though **psammoma bodies are NOT characteristic of lung cancer** and are typically seen in papillary thyroid carcinoma, serous ovarian carcinoma, and meningioma.
- While the patient has asbestos exposure raising concern for **mesothelioma**, this tumor typically shows epithelioid or sarcomatoid patterns without psammoma bodies, and the clinical presentation with **SIADH** and hyponatremia strongly favors SCLC over mesothelioma.
Lung tumors (primary and metastatic) US Medical PG Question 4: A 72-year-old man presents to the physician with blood in his sputum for 3 days. He also mentions that he has had a cough for the last 3 months but thought that it was because of the winter season. He also has often experienced fatigue recently. His temperature is 37.0°C (98.6°F), the respiratory rate is 15/min, the pulse is 67/min, and the blood pressure is 122/98 mm Hg. Auscultation of his chest reveals normal heart sounds but localized rhonchi over the right infrascapular region. A detailed diagnostic evaluation including a complete blood count and other serum biochemistry, chest radiogram, computed tomography of chest and abdomen, magnetic resonance imaging of the brain, bone scan, and pulmonary function tests are ordered, which confirm a diagnosis of limited-disease small cell lung cancer of 2.5 cm (1 in) in diameter, located in the lower lobe of the right lung, with the involvement of ipsilateral hilar lymph nodes and intrapulmonary lymph nodes. The mediastinal, subcarinal, scalene or supraclavicular lymph nodes are not involved, and there is no distant metastasis. There is no additional comorbidity and his performance status is good. The patient does not have any contraindication to any chemotherapeutic agents or radiotherapy. Which of the following is the best treatment option for this patient?
- A. Thoracic radiation therapy followed by prophylactic cranial irradiation
- B. Platinum-based chemotherapy plus etoposide and thoracic radiation therapy (Correct Answer)
- C. Lobectomy with adjuvant topotecan-based chemotherapy
- D. Pneumonectomy with adjuvant platinum-based chemotherapy and thoracic radiation therapy
- E. Topotecan-based chemotherapy plus thoracic radiation therapy
Lung tumors (primary and metastatic) Explanation: ***Platinum-based chemotherapy plus etoposide and thoracic radiation therapy***
- For **limited-stage small cell lung cancer (SCLC)**, combined modality treatment with **platinum-based chemotherapy (cisplatin or carboplatin) and etoposide** given concurrently with **thoracic radiation therapy** is the standard of care as it improves survival.
- This patient has limited-stage disease, defined as disease confined to one hemithorax and regional lymph nodes that can be encompassed within a tolerable radiation field.
*Thoracic radiation therapy followed by prophylactic cranial irradiation*
- While **prophylactic cranial irradiation (PCI)** is indicated for limited-stage SCLC after systemic therapy to reduce brain metastases, it's not the initial primary treatment by itself.
- **Chemotherapy** is a mandatory component of initial treatment for SCLC due to its highly metastatic nature.
*Lobectomy with adjuvant topotecan-based chemotherapy*
- **Surgery (lobectomy or pneumonectomy)** is generally not indicated for SCLC, even in limited stages, because it is a highly aggressive and systemic disease that responds better to chemotherapy and radiation.
- **Topotecan** is typically used as a second-line agent for recurrent or refractory SCLC, not as adjuvant therapy after surgery.
*Pneumonectomy with adjuvant platinum-based chemotherapy and thoracic radiation therapy*
- **Pneumonectomy** is an extensive surgery with significant morbidity and mortality and is rarely, if ever, performed for SCLC.
- While chemotherapy and radiation are components of treatment, **surgical resection (pneumonectomy in this case)** is not the standard primary therapy for SCLC given its systemic nature.
*Topotecan-based chemotherapy plus thoracic radiation therapy*
- **Topotecan** is generally reserved for **relapsed or refractory SCLC** as a second-line or later agent.
- The standard first-line chemotherapy for limited-stage SCLC involves a **platinum agent (cisplatin or carboplatin) with etoposide**.
Lung tumors (primary and metastatic) US Medical PG Question 5: An 82-year-old man is brought to the emergency department after he was found down by his daughter. On presentation, he is alert and oriented with no obvious signs of trauma. He says that he felt lightheaded shortly before passing out and that he has been feeling extremely fatigued over the last few weeks. He has a known diagnosis of colorectal adenocarcinoma and had it surgically removed 2 months ago; however, recently he has been feeling increasingly short of breath. He has a 60-pack-year smoking history and drinks 2-3 beers a night. He worked as an insulation technician and shipyard laborer for 40 years prior to retiring at age 65. Radiographs reveal approximately a dozen new nodules scattered throughout his lungs bilaterally. Biopsy of these lesions would most likely reveal which of the following?
- A. Pleomorphic giant cells
- B. Small dark blue cells that stain for chromogranin
- C. Flat cells with keratin pearls and intercellular bridges
- D. Psammoma bodies
- E. Mucin-producing glandular structures (Correct Answer)
Lung tumors (primary and metastatic) Explanation: ***Mucin-producing glandular structures***
- The patient has a history of **colorectal adenocarcinoma**, and the numerous new lung nodules suggest **metastatic spread** from the primary tumor.
- **Adenocarcinoma of the colon** is characterized by the formation of glands that typically produce mucin.
*Pleomorphic giant cells*
- This description is characteristic of **undifferentiated giant cell carcinoma**, a rare and aggressive subtype of **lung cancer**.
- While lung cancer is possible given the patient's smoking and occupational history, the history of colorectal adenocarcinoma and findings of multiple nodules strongly point towards metastasis rather than a primary lung tumor of this specific subtype.
*Small dark blue cells that stain for chromogranin*
- These features describe **small cell carcinoma**, a type of neuroendocrine tumor often found in the lungs, strongly associated with smoking.
- However, the patient's primary diagnosis of **colorectal adenocarcinoma** makes metastatic colorectal cancer to the lung a more direct and probable explanation for the new lung nodules.
*Flat cells with keratin pearls and intercellular bridges*
- This is the histological description of **squamous cell carcinoma**, which can occur in the lung and is also strongly associated with smoking and occupational exposures.
- While possible as a new primary lung cancer, the established diagnosis of **colorectal adenocarcinoma** and the pattern of multiple nodules make metastatic disease more likely.
*Psammoma bodies*
- These concentric calcifications are characteristic of several tumors, including **papillary thyroid carcinoma**, **meningiomas**, and **serous ovarian adenocarcinoma**.
- They are not typically associated with **colorectal adenocarcinoma** or its common metastatic presentations.
Lung tumors (primary and metastatic) US Medical PG Question 6: A 75-year-old gentleman is brought to the ED with confusion that started earlier this morning. His family notes that he was complaining of feeling weak last night and also had a slight tremor at the time. He is afebrile and he has no known chronic medical conditions. Physical exam reveals a cooperative but confused gentleman. His mucous membranes are moist, he has no focal neurological deficits, and his skin turgor is within normal limits. His lab results are notable for:
Serum Na+: 123 mEq/L
Plasma osmolality: 268 mOsm/kg
Urine osmolality: 349 mOsm/kg
Urine Na+: 47 mEq/L
Which of the following malignancies is most likely to be responsible for this patient's presentation?
- A. Gastric adenocarcinoma
- B. Small cell lung cancer (Correct Answer)
- C. Esophageal squamous cell carcinoma
- D. Non-seminomatous germ cell tumor
- E. Rib osteosarcoma
Lung tumors (primary and metastatic) Explanation: ***Small cell lung cancer***
- This patient's laboratory values (hyponatremia, low plasma osmolality, and inappropriately high urine osmolality with elevated urine sodium) are classic for the **Syndrome of Inappropriate Antidiuretic Hormone (SIADH)**.
- **Small cell lung cancer** is the most common malignancy associated with paraneoplastic SIADH due to its ability to ectopically produce ADH.
*Gastric adenocarcinoma*
- While gastric adenocarcinomas can cause paraneoplastic syndromes, SIADH is an **uncommon** paraneoplastic manifestation of this type of cancer.
- Other paraneoplastic syndromes, such as **Trousseau's syndrome** (migratory thrombophlebitis), are more classically associated with gastric adenocarcinoma.
*Esophageal squamous cell carcinoma*
- Esophageal cancer, including squamous cell carcinoma, is **rarely associated** with SIADH.
- Its paraneoplastic manifestations are less defined and not prominent for ADH production.
*Non-seminomatous germ cell tumor*
- Germ cell tumors, particularly non-seminomatous types, are more commonly associated with paraneoplastic syndromes involving **human chorionic gonadotropin (hCG)** or **alpha-fetoprotein (AFP)** production.
- While some germ cell tumors *can* release ADH, it is **not a primary cause** of SIADH compared to small cell lung cancer.
*Rib osteosarcoma*
- Osteosarcoma is a primary bone tumor and is **not typically associated** with paraneoplastic syndromes like SIADH.
- Its primary clinical manifestations are related to local bone destruction and metastasis.
Lung tumors (primary and metastatic) US Medical PG Question 7: A 34-year-old man comes to the physician because of a 3-week history of left testicular swelling. He has no pain. He underwent a left inguinal hernia repair as a child. He takes no medications. He appears healthy. His vital signs are within normal limits. Examination shows an enlarged, nontender left testicle. When the patient is asked to cough, there is no bulge present in the scrotum. When a light is held behind the scrotum, it does not shine through. There is no inguinal lymphadenopathy. Laboratory studies show:
Hemoglobin 14.5 g/dL
Leukocyte count 8,800/mm3
Platelet count 345,000/mm3
Serum
Glucose 88 mg/dL
Creatinine 0.8 mg/dL
Total bilirubin 0.7 mg/dL
Alkaline phosphatase 35 U/L
AST 15 U/L
ALT 14 U/L
Lactate dehydrogenase 60 U/L
β-Human chorionic gonadotropin 80 mIU/mL (N < 5)
α-Fetoprotein 6 ng/mL (N < 10)
Which of the following is the most likely diagnosis?
- A. Seminoma (Correct Answer)
- B. Leydig cell tumor
- C. Choriocarcinoma
- D. Spermatocele of testis
- E. Yolk sac tumor
Lung tumors (primary and metastatic) Explanation: **Seminoma**
- The elevated **beta-human chorionic gonadotropin (β-hCG)** in the presence of a normal alpha-fetoprotein (α-FP) is highly suggestive of seminoma, especially in a painless testicular mass in a young man.
- While AFP is typically not elevated in pure seminomas, β-hCG can be mildly to moderately elevated in approximately 10-30% of cases, consistent with this presentation.
*Leydig cell tumor*
- These tumors often produce androgens or estrogens, leading to symptoms like **precocious puberty** in boys or **gynecomastia** in adult men, which are not described.
- Serum tumor markers like β-hCG and α-FP are typically **not elevated** in Leydig cell tumors.
*Choriocarcinoma*
- This highly aggressive germ cell tumor is characterized by **markedly elevated β-hCG levels**, often much higher than 80 mIU/mL, and can also elevate α-FP.
- Given the relatively mild β-hCG elevation and normal α-FP, choriocarcinoma is less likely.
*Spermatocele of testis*
- A spermatocele is a **benign cyst** that typically transilluminates (light shines through), which is absent in this case.
- Tumor markers like β-hCG and α-FP would be **normal** in a spermatocele, ruling it out.
*Yolk sac tumor*
- Yolk sac tumors are characterized by **elevated alpha-fetoprotein (α-FP)** levels, which are normal in this patient.
- While they can also elevate β-hCG in some cases, the defining marker, α-FP, is not elevated here.
Lung tumors (primary and metastatic) US Medical PG Question 8: A 57-year-old man is brought to the emergency department by his wife 20 minutes after having had a seizure. He has had recurrent headaches and dizziness for the past 2 weeks. An MRI of the brain shows multiple, round, well-demarcated lesions in the brain parenchyma at the junction between gray and white matter. This patient's brain lesions are most likely comprised of cells that originate from which of the following organs?
- A. Kidney
- B. Skin
- C. Lung (Correct Answer)
- D. Thyroid
- E. Prostate
Lung tumors (primary and metastatic) Explanation: ***Lung (Correct Answer)***
- **Lung cancer** is the most common cause of **brain metastases** in adults, accounting for approximately **50% of all cases**
- The clinical presentation—seizure, headaches, dizziness, and **multiple, round, well-demarcated lesions at the gray-white matter junction**—is classic for metastatic lung cancer
- Both **small cell and non-small cell lung cancers** have high propensity for hematogenous spread to the brain
- The watershed areas at the gray-white junction are common sites due to lodging of tumor emboli in terminal arterioles
*Kidney (Incorrect)*
- **Renal cell carcinoma (RCC)** can metastasize to the brain but accounts for only **5-10% of brain metastases**
- While RCC metastases can appear similar on imaging, lung cancer is statistically more likely given its higher prevalence
- RCC metastases are often **highly vascular and may hemorrhage**, which is not mentioned in this case
*Skin (Incorrect)*
- **Melanoma** has the **highest propensity per case** to metastasize to the brain among all cancers
- However, the **overall incidence of melanoma is much lower** than lung cancer, making it a less probable primary source
- Melanoma brain metastases often present as **hemorrhagic lesions** and would typically have skin findings or history
*Thyroid (Incorrect)*
- **Thyroid cancer** rarely metastasizes to the brain (accounts for <1% of brain metastases)
- Brain metastases from thyroid cancer typically occur in **advanced papillary or follicular carcinoma** or in **anaplastic thyroid cancer**
- More common metastatic sites for thyroid cancer are lung and bone
*Prostate (Incorrect)*
- **Prostate cancer very rarely metastasizes to the brain** (<1% of cases)
- Prostate cancer preferentially metastasizes to **bone (especially axial skeleton), lymph nodes, and liver**
- Brain metastases from prostate cancer suggest extremely advanced, aggressive disease and are exceptionally uncommon
Lung tumors (primary and metastatic) US Medical PG Question 9: A 31 year-old African-American female presents with painful shin nodules, uveitis, and calcified hilar lymph nodes. A transbronchial biopsy of the lung would most likely show which of the following histologies?
- A. Golden-brown fusiform rods
- B. Inflammation, fibrosis and cyst formation that is most prominent in subpleural regions
- C. Non-caseating granulomas (Correct Answer)
- D. Silica particles (birefringent) surrounded by collagen
- E. Patchy interstitial lymphoid infiltrate into walls of alveolar units
Lung tumors (primary and metastatic) Explanation: ***Non-caseating granulomas***
- The constellation of **erythema nodosum** (painful shin nodules), **uveitis**, and **hilar lymphadenopathy** in an African-American female is highly characteristic of **sarcoidosis**.
- **Sarcoidosis** is pathologically defined by the presence of **non-caseating granulomas** in affected tissues, which would be visible on a transbronchial biopsy.
*Golden-brown fusiform rods*
- These are **ferruginous bodies**, characteristic of **asbestosis**, which is not supported by the patient's presentation.
- Asbestosis would typically involve a history of **asbestos exposure** and present with **pleural plaques** or **interstitial fibrosis**.
*Inflammation, fibrosis and cyst formation that is most prominent in subpleural regions*
- This description is more indicative of **pulmonary Langerhans cell histiocytosis**, a rare disease usually associated with **smoking**.
- It does not align with the patient's specific systemic manifestations like uveitis or erythema nodosum.
*Silica particles (birefringent) surrounded by collagen*
- This describes the histological findings of **silicosis**, an occupational lung disease resulting from exposure to **silica dust**.
- Silicosis is not typically associated with uveitis or erythema nodosum.
*Patchy interstitial lymphoid infiltrate into walls of alveolar units*
- This pattern can be seen in various interstitial lung diseases, but it is not specific for sarcoidosis.
- It could be found in conditions like **lymphoid interstitial pneumonia**, which does not fit the overall clinical picture.
Lung tumors (primary and metastatic) US Medical PG Question 10: A 54-year-old man comes to the emergency department for nausea and vomiting for the past 2 days. The patient reports that he felt tired and weak for the past week without any obvious precipitating factors. Past medical history is significant for hypertension controlled with hydrochlorothiazide. He denies diarrhea, changes in diet, recent surgery, vision changes, or skin pigmentation but endorses a 10-lb weight loss, headaches, fatigue, and a chronic cough for 2 years. He smokes 2 packs per day for the past 20 years but denies alcohol use. Physical examination demonstrates generalized weakness with no peripheral edema. Laboratory tests are shown below:
Serum:
Na+: 120 mEq/L
Cl-: 97 mEq/L
K+: 3.4 mEq/L
HCO3-: 24 mEq/L
Ca2+: 10 mg/dL
Osmolality: 260 mOsm/L
Urine:
Na+: 25 mEq/L
Osmolality: 285 mOsm/L
Specific gravity: 1.007
What is the most likely finding in this patient?
- A. Antibodies against presynaptic calcium channels
- B. Pituitary hypertrophy
- C. Chromogranin positive mass in the lung (Correct Answer)
- D. Venous congestion at the liver
- E. Orphan Annie eyes and psammoma bodies in the thyroid
Lung tumors (primary and metastatic) Explanation: ***Chromogranin positive mass in the lung***
- The patient presents with **hyponatremia**, **low serum osmolality (260 mOsm/L)**, and **inappropriately high urine osmolality (285 mOsm/L)** and urine sodium (25 mEq/L), which are characteristic findings of the **Syndrome of Inappropriate Antidiuretic Hormone (SIADH)**.
- While **hydrochlorothiazide can cause hyponatremia**, the patient's **20-pack-year smoking history**, **chronic cough for 2 years**, **weight loss**, and **fatigue** strongly suggest an underlying malignancy rather than simple medication effect.
- The most likely cause of SIADH in this patient is **small cell lung carcinoma (SCLC)**, which is a **neuroendocrine tumor** that commonly secretes ADH ectopically and stains positive for **chromogranin A**, a neuroendocrine marker.
- SCLC is the most common malignancy associated with SIADH and frequently presents with paraneoplastic syndromes in heavy smokers.
*Antibodies against presynaptic calcium channels*
- This finding is characteristic of **Lambert-Eaton myasthenic syndrome (LEMS)**, which is a paraneoplastic syndrome associated with small cell lung cancer caused by antibodies against voltage-gated calcium channels.
- While LEMS can occur in patients with SCLC, the presented symptoms and laboratory findings (specifically euvolemic hyponatremia consistent with SIADH) point more directly to **ectopic ADH secretion** from the tumor rather than a neuromuscular disorder.
- LEMS typically presents with proximal muscle weakness that improves with repeated use, which is not described in this patient.
*Pituitary hypertrophy*
- **Pituitary adenomas** can cause various endocrine abnormalities, but they do not typically cause SIADH.
- SIADH from pituitary pathology is rare and would not explain the **pulmonary symptoms** (chronic cough) or the patient's **significant smoking history**.
- This does not fit the overall clinical picture as well as small cell lung carcinoma.
*Venous congestion at the liver*
- **Hepatic venous congestion** occurs in conditions like right-sided heart failure, constrictive pericarditis, or Budd-Chiari syndrome.
- The patient has **no signs of volume overload** (no peripheral edema, and exam shows generalized weakness only).
- While heart failure can cause hyponatremia, it typically presents with hypervolemic hyponatremia with signs of fluid overload, which is absent in this case.
*Orphan Annie eyes and psammoma bodies in the thyroid*
- These are characteristic histological features of **papillary thyroid carcinoma**.
- There is **no clinical evidence** of thyroid pathology (e.g., thyroid nodule, neck mass, dysphagia, hoarseness) in this patient.
- Papillary thyroid carcinoma is not associated with SIADH or the paraneoplastic syndromes seen in this case.
More Lung tumors (primary and metastatic) US Medical PG questions available in the OnCourse app. Practice MCQs, flashcards, and get detailed explanations.
