A 50-year-old male is brought to the dermatologist's office with complaints of a pigmented lesion. The lesion is uniformly dark with clean borders and no asymmetry and has been increasing in size over the past two weeks. He works in construction and spends large portions of his day outside. The dermatologist believes that this mole should be biopsied. To prepare the patient for the biopsy, the dermatologist injects a small amount of lidocaine into the skin around the lesion. Which of the following nerve functions would be the last to be blocked by the lidocaine?
Q2
A 59-year-old woman presents to the emergency room with severe low back pain. She reports pain radiating down her left leg into her left foot. She also reports intermittent severe lower back spasms. The pain started after lifting multiple heavy boxes at her work as a grocery store clerk. She denies bowel or bladder dysfunction. Her past medical history is notable for osteoporosis and endometrial cancer. She underwent a hysterectomy 20 years earlier. She takes alendronate. Her temperature is 99°F (37.2°C), blood pressure is 135/85 mmHg, pulse is 85/min, and respirations are 22/min. Her BMI is 21 kg/m^2. On exam, she is unable to bend over due to pain. Her movements are slowed to prevent exacerbating her muscle spasms. A straight leg raise elicits severe radiating pain into her left lower extremity. The patient reports that the pain is worst along the posterior thigh and posterolateral leg into the fourth and fifth toes. Palpation along the lumbar vertebral spines demonstrates mild tenderness. Patellar reflexes are 2+ bilaterally. The Achilles reflex is decreased on the left. Which nerve root is most likely affected in this patient?
Q3
A 27-year-old woman develops progressive difficulty breathing after a long day of chores in a dusty house. These chores included brushing the family dog, vacuuming, dusting, and sweeping. She occasionally gets these episodes once or twice a year and has her medication on hand. Her symptoms are reversed by inhaling a β2-adrenergic receptor agonist. Which of the following chemical mediators is responsible for this patient’s breathing difficulties?
Q4
A researcher is studying how electrical activity propagates across the heart. In order to do this, he decides to measure the rate at which an action potential moves within various groups of cardiac muscle tissue. In particular, he isolates fibers from areas of the heart with the following characteristics:
A) Dysfunction leads to fixed PR intervals prior to a dropped beat
B) Dysfunction leads to increasing PR intervals prior to a dropped beat
C) Dysfunction leads to tachycardia with a dramatically widened QRS complex
D) Dysfunction leads to tachycardia with a sawtooth pattern on electrocardiogram
Which of the following is the proper order of these tissues from fastest action potential propagation to slowest action potential propagation.
Q5
A 14-year-old boy is brought to the emergency department because of acute left-sided chest pain and dyspnea following a motor vehicle accident. His pulse is 122/min and blood pressure is 85/45 mm Hg. Physical examination shows distended neck veins and tracheal displacement to the right side. The left chest is hyperresonant to percussion and there are decreased breath sounds. This patient would most benefit from needle insertion at which of the following anatomical sites?
Q6
A 24-year-old woman presents to the emergency department for chest pain and shortness of breath. She was at home making breakfast when her symptoms began. She describes the pain as sharp and located in her chest. She thought she was having a heart attack and began to feel short of breath shortly after. The patient is a college student and recently joined the soccer team. She has no significant past medical history except for a progesterone intrauterine device which she uses for contraception, and a cyst in her breast detected on ultrasound. Last week she returned on a trans-Atlantic flight from Russia. Her temperature is 98.4°F (36.9°C), blood pressure is 137/69 mmHg, pulse is 98/min, respirations are 18/min, and oxygen saturation is 99% on room air. Physical exam reveals an anxious young woman. Cardiac and pulmonary exam are within normal limits. Deep inspiration and palpation of the chest wall elicits pain. Neurologic exam reveals a stable gait and cranial nerves II-XII are grossly intact. Which of the following best describes the most likely underlying etiology?
Q7
A 35-year-old woman volunteers for a study on respiratory physiology. Pressure probes A and B are placed as follows:
Probe A: between the parietal and visceral pleura
Probe B: within the cavity of an alveolus
The probes provide a pressure reading relative to atmospheric pressure. To obtain a baseline reading, she is asked to sit comfortably and breathe normally. Which of the following sets of values will most likely be seen at the end of inspiration?
Q8
Which neurotransmitter is primarily responsible for parasympathetic effects on heart rate?
Q9
A 56-year-old man with a significant past medical history of diabetes mellitus, hypertension, and hypercholesterolemia is brought to the emergency department by his wife. The wife states the symptoms started 1 hour ago when she noticed that he was having difficulty swallowing his breakfast and that his voice was hoarse. The patient had a recent admission for a transient ischemic attack but was not compliant with his discharge instructions and medication. Examination of the eye shows left-sided partial ptosis and miosis along with diplopia and nystagmus. During the examination, it is noted that the right side of the face and body has markedly more sweating than the left side. An MRI of the brain reveals an ischemic infarct at the level of the left lateral medulla. Which of the following most likely accounts for this patient’s symptoms?
Q10
A 45-year-old woman comes to the physician because of progressive difficulty swallowing solids and liquids over the past 4 months. She has lost 4 kg (9 lb) during this period. There is no history of serious illness. She emigrated to the US from Panama 7 years ago. She does not smoke cigarettes or drink alcohol. Cardiopulmonary examination shows a systolic murmur and an S3 gallop. A barium radiograph of the chest is shown. Histopathologic examination of the esophageal wall is most likely to show which of the following?
Autonomic innervation of thoracic organs US Medical PG Practice Questions and MCQs
Question 1: A 50-year-old male is brought to the dermatologist's office with complaints of a pigmented lesion. The lesion is uniformly dark with clean borders and no asymmetry and has been increasing in size over the past two weeks. He works in construction and spends large portions of his day outside. The dermatologist believes that this mole should be biopsied. To prepare the patient for the biopsy, the dermatologist injects a small amount of lidocaine into the skin around the lesion. Which of the following nerve functions would be the last to be blocked by the lidocaine?
A. Pain
B. Touch
C. Temperature
D. Sympathetic stimulation
E. Pressure (Correct Answer)
Explanation: ***Pressure***
- **Pressure** sensation is mediated by **Aβ fibers**, which are relatively **larger** and **myelinated**, making them more resistant to local anesthetic blockade.
- Nerve fibers are blocked in a specific order, typically starting with smaller, unmyelinated fibers and ending with larger, myelinated fibers.
*Pain*
- **Pain** sensation is primarily carried by **unmyelinated C fibers** and **small myelinated Aδ fibers**, which are among the **first to be blocked** by local anesthetics.
- These fibers have a **high surface-to-volume ratio**, making them more susceptible to the action of lidocaine.
*Touch*
- **Touch** sensation is mediated by a mix of **Aβ and Aδ fibers**; light touch is typically blocked relatively early due to the involvement of smaller fibers.
- However, **crude touch** often persists longer than pain and temperature but is usually blocked before pressure.
*Temperature*
- **Temperature** sensation is primarily carried by **Aδ and C fibers**, making it one of the **earliest sensations to be blocked** by local anesthetic.
- These fibers are generally small and have high sensitivity to local anesthetic agents.
*Sympathetic stimulation*
- **Sympathetic nerve fibers** are typically **small, unmyelinated C fibers** and are generally the **first to be blocked** by local anesthetics.
- This early blockade can lead to **vasodilation** in the area due to the loss of sympathetic tone.
Question 2: A 59-year-old woman presents to the emergency room with severe low back pain. She reports pain radiating down her left leg into her left foot. She also reports intermittent severe lower back spasms. The pain started after lifting multiple heavy boxes at her work as a grocery store clerk. She denies bowel or bladder dysfunction. Her past medical history is notable for osteoporosis and endometrial cancer. She underwent a hysterectomy 20 years earlier. She takes alendronate. Her temperature is 99°F (37.2°C), blood pressure is 135/85 mmHg, pulse is 85/min, and respirations are 22/min. Her BMI is 21 kg/m^2. On exam, she is unable to bend over due to pain. Her movements are slowed to prevent exacerbating her muscle spasms. A straight leg raise elicits severe radiating pain into her left lower extremity. The patient reports that the pain is worst along the posterior thigh and posterolateral leg into the fourth and fifth toes. Palpation along the lumbar vertebral spines demonstrates mild tenderness. Patellar reflexes are 2+ bilaterally. The Achilles reflex is decreased on the left. Which nerve root is most likely affected in this patient?
A. L5
B. S2
C. L3
D. L4
E. S1 (Correct Answer)
Explanation: ***S1***
- Pain radiating to the **posterior thigh**, **posterolateral leg**, and into the **fourth and fifth toes** is characteristic of **S1 dermatome involvement**.
- A **decreased Achilles reflex** (ankle jerk reflex) specifically points to compromise of the **S1 nerve root**.
*L5*
- **L5 radiculopathy** typically causes pain and sensory deficits in the **dorsum of the foot** and into the **first, second, and third toes**.
- Motor weakness often affects **foot dorsiflexion** and **toe extension**, not primarily the Achilles reflex.
*S2*
- **S2 radiculopathy** would primarily affect sensation along the **posterior thigh** and **calf**, with possible involvement of the **plantar aspect of the foot**.
- It does not typically cause a decrease in the **Achilles reflex**, which is predominantly S1.
*L3*
- **L3 radiculopathy** typically presents with pain and sensory changes along the **anterior thigh** and possibly the **medial knee**.
- It can affect the **patellar reflex**, which is intact in this patient, and does not cause pain in the posterior leg or foot.
*L4*
- **L4 radiculopathy** typically causes pain and sensory changes over the **anterior thigh**, **medial leg**, and potentially the **medial malleolus**.
- It often presents with weakness in **quadriceps muscle** and can cause a diminished **patellar reflex**, which is normal in this patient.
Question 3: A 27-year-old woman develops progressive difficulty breathing after a long day of chores in a dusty house. These chores included brushing the family dog, vacuuming, dusting, and sweeping. She occasionally gets these episodes once or twice a year and has her medication on hand. Her symptoms are reversed by inhaling a β2-adrenergic receptor agonist. Which of the following chemical mediators is responsible for this patient’s breathing difficulties?
A. Histamine
B. Leukotrienes (Correct Answer)
C. Serotonin
D. Bradykinin
E. Endorphins
Explanation: ***Correct: Leukotrienes***
- Leukotrienes, particularly **leukotriene C4, D4, and E4**, are potent **bronchoconstrictors** and are significantly involved in the pathogenesis of **asthma**.
- They also contribute to **bronchial hyperreactivity**, mucus secretion, and airway edema, all hallmarks of asthmatic exacerbations triggered by allergens and irritants.
*Incorrect: Histamine*
- Histamine is released by mast cells and basophils, causing **bronchoconstriction** and vasodilation, but its role in the **sustained and severe bronchospasm of asthma** is less prominent than leukotrienes.
- While it contributes to immediate hypersensitivity reactions, **antihistamines are generally not effective in treating asthma exacerbations**.
*Incorrect: Serotonin*
- Serotonin (5-hydroxytryptamine) is primarily involved in smooth muscle contraction and platelet aggregation, but it is **not a primary mediator of bronchoconstriction in human asthma**.
- Its effects on the airways are relatively minor compared to other mediators.
*Incorrect: Bradykinin*
- Bradykinin is a peptide that causes **vasodilation**, increased vascular permeability, and pain, and can induce **bronchoconstriction**, especially in sensitive individuals.
- However, it is **not considered a primary or dominant mediator in typical allergic asthma exacerbations** as described in this patient.
*Incorrect: Endorphins*
- Endorphins are **endogenous opioid peptides** that primarily act as **neurotransmitters** and neuromodulators, involved in pain sensation and mood regulation.
- They have **no direct role in the acute pathophysiology of asthma** or bronchoconstriction.
Question 4: A researcher is studying how electrical activity propagates across the heart. In order to do this, he decides to measure the rate at which an action potential moves within various groups of cardiac muscle tissue. In particular, he isolates fibers from areas of the heart with the following characteristics:
A) Dysfunction leads to fixed PR intervals prior to a dropped beat
B) Dysfunction leads to increasing PR intervals prior to a dropped beat
C) Dysfunction leads to tachycardia with a dramatically widened QRS complex
D) Dysfunction leads to tachycardia with a sawtooth pattern on electrocardiogram
Which of the following is the proper order of these tissues from fastest action potential propagation to slowest action potential propagation.
A. B > D > C > A
B. D > C > A > B
C. B > C > D > A
D. A > D > C > B (Correct Answer)
E. A > C > D > B
Explanation: ***A > D > C > B***
* **Purkinje fibers (A)** have the fastest conduction velocity in the heart to ensure rapid and synchronous ventricular depolarization. The description of "fixed PR intervals prior to a dropped beat" in **Mobitz type II second-degree AV block** indicates an issue with conduction distal to the AV node, often in the His-Purkinje system, while still maintaining typical conduction through the atria and AV node for conducted beats.
* **Atrial muscle (D)** has a faster conduction velocity than the AV node but slower than Purkinje fibers. The "sawtooth pattern on electrocardiogram" unequivocally points to **atrial flutter**, which is characterized by rapid, regular depolarization of the atria.
* **Ventricular muscle (C)** has a conduction velocity slower than Purkinje fibers but faster than the AV node. "Tachycardia with a dramatically widened QRS complex" is characteristic of **ventricular tachycardia (VT)**, which arises from abnormal electrical activity within the ventricles.
* **AV node (B)** has the slowest conduction velocity in the heart, which allows for proper ventricular filling. "Increasing PR intervals prior to a dropped beat" describes **Mobitz type I second-degree AV block (Wenckebach phenomenon)**, which is due to progressive prolongation of conduction delay within the AV node itself.
*B > D > C > A*
* This order incorrectly places the **AV node (B)** as the fastest and **Purkinje fibers (A)** as the slowest, which is contrary to the known conduction velocities in the heart.
* The AV node is critical for delaying the impulse, making it the slowest, while Purkinje fibers are designed for rapid spread, making them the fastest.
*D > C > A > B*
* This option incorrectly places **atrial muscle (D)** as faster than **Purkinje fibers (A)**. Purkinje fibers have the fastest conduction velocity in the heart, considerably faster than atrial muscle.
*B > C > D > A*
* This arrangement incorrectly lists the **AV node (B)** as the fastest and **Purkinje fibers (A)** as the slowest. The AV node is the slowest for its physiological role of delaying ventricular contraction, while Purkinje fibers are optimized for rapid conduction.
*A > C > D > B*
* While placing **Purkinje fibers (A)** as the fastest and the **AV node (B)** as the slowest is correct, this order incorrectly places **ventricular muscle (C)** as faster than **atrial muscle (D)**. Atrial muscle generally conducts faster than ventricular muscle in normal physiology.
Question 5: A 14-year-old boy is brought to the emergency department because of acute left-sided chest pain and dyspnea following a motor vehicle accident. His pulse is 122/min and blood pressure is 85/45 mm Hg. Physical examination shows distended neck veins and tracheal displacement to the right side. The left chest is hyperresonant to percussion and there are decreased breath sounds. This patient would most benefit from needle insertion at which of the following anatomical sites?
A. 5th left intercostal space along the midclavicular line
B. 8th left intercostal space along the posterior axillary line
C. 2nd left intercostal space along the midclavicular line (Correct Answer)
D. Subxiphoid space in the left sternocostal margin
E. 5th left intercostal space along the midaxillary line
Explanation: ***2nd left intercostal space along the midclavicular line***
- The patient's symptoms (chest pain, dyspnea, hypotension, distended neck veins, tracheal deviation, hyperresonance, and decreased breath sounds on the left) are classic signs of a **tension pneumothorax**.
- Immediate treatment for **tension pneumothorax** involves needle decompression at the **2nd intercostal space** in the midclavicular line to relieve pressure and restore hemodynamic stability.
*5th left intercostal space along the midclavicular line*
- This location is typically used for **chest tube insertion** in a more controlled setting, not for emergent needle decompression of a tension pneumothorax.
- While it's a safe location for pleural access, it is not the **first-line site** for immediate life-saving decompression.
*8th left intercostal space along the posterior axillary line*
- This site is too low and posterior for effective needle decompression of a tension pneumothorax, which requires rapid access to the **apex of the lung**.
- It is more commonly used for **thoracentesis** to drain fluid from the pleural cavity.
*Subxiphoid space in the left sternocostal margin*
- This location is primarily used for **pericardiocentesis** to drain fluid from the pericardial sac in cases of cardiac tamponade.
- It is not appropriate for addressing a **pneumothorax**, which involves air in the pleural space.
*5th left intercostal space along the midaxillary line*
- This site is a common alternative for **chest tube insertion** but is not the preferred or most immediate site for needle decompression of a tension pneumothorax.
- While it offers pleural access, the **2nd intercostal space** anteriorly is chosen for expediency and safety in an emergency.
Question 6: A 24-year-old woman presents to the emergency department for chest pain and shortness of breath. She was at home making breakfast when her symptoms began. She describes the pain as sharp and located in her chest. She thought she was having a heart attack and began to feel short of breath shortly after. The patient is a college student and recently joined the soccer team. She has no significant past medical history except for a progesterone intrauterine device which she uses for contraception, and a cyst in her breast detected on ultrasound. Last week she returned on a trans-Atlantic flight from Russia. Her temperature is 98.4°F (36.9°C), blood pressure is 137/69 mmHg, pulse is 98/min, respirations are 18/min, and oxygen saturation is 99% on room air. Physical exam reveals an anxious young woman. Cardiac and pulmonary exam are within normal limits. Deep inspiration and palpation of the chest wall elicits pain. Neurologic exam reveals a stable gait and cranial nerves II-XII are grossly intact. Which of the following best describes the most likely underlying etiology?
A. Ischemia of the myocardium
B. Clot in the pulmonary veins
C. Psychogenic etiology
D. Musculoskeletal inflammation
E. Clot in the pulmonary arteries (Correct Answer)
Explanation: ***Clot in the pulmonary arteries***
- This patient has **significant risk factors for pulmonary embolism (PE)**: recent **trans-Atlantic flight** (prolonged immobilization) and **progesterone IUD** (hormonal contraception increases thrombotic risk).
- Classic PE symptoms include **acute-onset pleuritic chest pain** and **shortness of breath**, both present here.
- **Key teaching point:** While the chest wall tenderness and normal vital signs might suggest a benign cause, **PE must be ruled out in high-risk patients** presenting to the ED with chest pain and dyspnea. Normal oxygen saturation and physical exam do not exclude PE.
- The **Wells criteria** would assign points for recent travel and symptoms consistent with PE, warranting further workup (D-dimer, CT pulmonary angiography).
- In emergency medicine, **risk factors take precedence** over reassuring physical findings when considering life-threatening diagnoses like PE.
*Ischemia of the myocardium*
- The patient is **24 years old** with no traditional cardiovascular risk factors (smoking, hypertension, diabetes, family history).
- The pain is **sharp and pleuritic**, not the typical crushing, substernal pressure of acute coronary syndrome.
- **Myocardial infarction is exceedingly rare** in this demographic without congenital abnormalities or cocaine use.
*Clot in the pulmonary veins*
- This represents an **anatomical misunderstanding** of PE pathophysiology.
- **Venous thromboemboli form in systemic veins** (typically deep veins of legs) and travel through the right heart to lodge in the **pulmonary arteries**, not veins.
- Pulmonary veins carry oxygenated blood from lungs to left atrium; obstruction here would cause pulmonary edema, not PE.
*Psychogenic etiology*
- While the patient appears **anxious**, attributing symptoms to panic/anxiety is a **diagnosis of exclusion**.
- **Critical error:** Dismissing symptoms as psychogenic in a patient with **clear PE risk factors** could lead to catastrophic outcomes if PE is missed.
- Panic attacks can mimic PE, but the recent flight and hormonal contraception mandate organic cause evaluation first.
*Musculoskeletal inflammation*
- The finding of **pain with palpation** and **deep inspiration** is classically associated with **costochondritis or chest wall strain**.
- This is a **reasonable consideration** and in many patients would be the correct diagnosis.
- **However:** The combination of **recent long-haul flight + hormonal contraception + acute dyspnea** creates a clinical scenario where PE **cannot be assumed away** based on chest wall tenderness alone.
- Pleuritic chest pain can occur with PE when it causes pleural irritation, and **PE can coexist with incidental chest wall tenderness**.
- The **standard of care** requires PE evaluation before attributing symptoms solely to musculoskeletal causes in this high-risk scenario.
Question 7: A 35-year-old woman volunteers for a study on respiratory physiology. Pressure probes A and B are placed as follows:
Probe A: between the parietal and visceral pleura
Probe B: within the cavity of an alveolus
The probes provide a pressure reading relative to atmospheric pressure. To obtain a baseline reading, she is asked to sit comfortably and breathe normally. Which of the following sets of values will most likely be seen at the end of inspiration?
A. Probe A: -6 mm Hg; Probe B: 0 mm Hg (Correct Answer)
B. Probe A: 0 mm Hg; Probe B: -1 mm Hg
C. Probe A: -4 mm Hg; Probe B: 0 mm Hg
D. Probe A: -4 mm Hg; Probe B: -1 mm Hg
E. Probe A: -6 mm Hg; Probe B: -1 mm Hg
Explanation: ***Probe A: -6 mm Hg; Probe B: 0 mm Hg***
- At the **end of inspiration**, the **intrapleural pressure (Probe A)** is at its most negative, typically around -6 to -8 cm H2O (equivalent to -4 to -6 mmHg), reflecting the maximum expansion of the thoracic cavity.
- At the **end of inspiration**, just before exhalation begins, there is **no airflow**, so the **intrapulmonary pressure (Probe B)** equalizes with atmospheric pressure, resulting in a 0 mm Hg reading.
*Probe A: 0 mm Hg; Probe B: -1 mm Hg*
- An **intrapleural pressure of 0 mm Hg** would indicate a **pneumothorax** since it should always be negative to prevent lung collapse.
- An **intrapulmonary pressure of -1 mm Hg** would indicate that **inspiration is still ongoing**, as air would be flowing into the lungs.
*Probe A: -4 mm Hg; Probe B: 0 mm Hg*
- While an **intrapulmonary pressure of 0 mm Hg** is correct at the end of inspiration, an **intrapleural pressure of -4 mm Hg** is typical for the **end of expiration (Functional Residual Capacity)** during quiet breathing, not the end of inspiration.
- The **intrapleural pressure becomes more negative** during inspiration due to increased thoracic volume, so -4 mm Hg would be insufficient.
*Probe A: -4 mm Hg; Probe B: -1 mm Hg*
- An **intrapleural pressure of -4 mm Hg** is the normal pressure at the **end of expiration**, not the end of inspiration, where it becomes more negative.
- An **intrapulmonary pressure of -1 mm Hg** indicates that **inspiration is still in progress**, not at its end, as air would still be flowing into the lungs.
*Probe A: -6 mm Hg; Probe B: -1 mm Hg*
- While an **intrapleural pressure of -6 mm Hg** is consistent with the end of inspiration, an **intrapulmonary pressure of -1 mm Hg** means that **airflow is still occurring into the lungs**.
- At the **very end of inspiration**, just before the start of exhalation, airflow momentarily ceases, and intrapulmonary pressure becomes zero relative to the atmosphere.
Question 8: Which neurotransmitter is primarily responsible for parasympathetic effects on heart rate?
A. Norepinephrine
B. Dopamine
C. Acetylcholine (Correct Answer)
D. Epinephrine
Explanation: ***Acetylcholine***
- **Acetylcholine** is the primary neurotransmitter released by postganglionic parasympathetic neurons.
- It acts on **muscarinic receptors** (M2 receptors) in the heart to decrease heart rate.
*Norepinephrine*
- **Norepinephrine** is primarily associated with the **sympathetic nervous system**, increasing heart rate and contractility.
- It acts on **beta-1 adrenergic receptors** in the heart.
*Dopamine*
- **Dopamine** is a precursor to norepinephrine and epinephrine, and primarily functions as a neurotransmitter in the **central nervous system** and in regulating renal blood flow.
- While it can have cardiac effects, it is not the primary neurotransmitter for parasympathetic actions on heart rate.
*Epinephrine*
- **Epinephrine** (adrenaline) is a hormone released by the adrenal medulla and a neurotransmitter in the sympathetic nervous system, causing an **increase in heart rate** and contractility.
- It works through **beta-1 adrenergic receptors**, antagonistic to parasympathetic effects.
Question 9: A 56-year-old man with a significant past medical history of diabetes mellitus, hypertension, and hypercholesterolemia is brought to the emergency department by his wife. The wife states the symptoms started 1 hour ago when she noticed that he was having difficulty swallowing his breakfast and that his voice was hoarse. The patient had a recent admission for a transient ischemic attack but was not compliant with his discharge instructions and medication. Examination of the eye shows left-sided partial ptosis and miosis along with diplopia and nystagmus. During the examination, it is noted that the right side of the face and body has markedly more sweating than the left side. An MRI of the brain reveals an ischemic infarct at the level of the left lateral medulla. Which of the following most likely accounts for this patient’s symptoms?
A. Postganglionic sympathetic lesion
B. Injury to the cervical sympathetic ganglia
C. 3rd-order neuron lesion
D. Denervation of the descending sympathetic tract (Correct Answer)
E. Preganglionic lesion at the lateral gray horn
Explanation: ***Denervation of the descending sympathetic tract***
- The patient's symptoms, including **dysphagia**, **hoarseness**, **facial anhidrosis** on the left, **miosis**, **ptosis**, **diplopia**, and **nystagmus**, are classic for **Wallenberg syndrome** (lateral medullary syndrome).
- This syndrome is caused by an infarct in the **lateral medulla**, which damages the **descending sympathetic tracts (1st-order neurons)**, leading to **Horner's syndrome** (miosis, ptosis, anhidrosis) on the ipsilateral side and contralateral hyperhidrosis due to lack of sympathetic tone to the affected side, along with other neurological deficits due to involvement of vital brainstem nuclei.
*Postganglionic sympathetic lesion*
- A postganglionic lesion (also called a **3rd-order neuron lesion**) would typically affect structures supplied by the superior cervical ganglion, such as the eye and face.
- However, it would not explain the other brainstem symptoms like **dysphagia**, **hoarseness**, **diplopia**, or **nystagmus**, which point to a central lesion in the medulla.
*Injury to the cervical sympathetic ganglia*
- An injury here would cause **Horner's syndrome** affecting the eye and face on the ipsilateral side.
- It would not account for the brainstem deficits like **dysphagia**, **hoarseness**, or **nystagmus**, nor the specific finding of an **ischemic infarct in the lateral medulla**.
*3rd-order neuron lesion*
- A 3rd-order neuron lesion is synonymous with a **postganglionic sympathetic lesion** and would cause **Horner's syndrome**.
- This would not explain the additional cranial nerve and brainstem signs found in this patient, which are characteristic of a **lateral medullary infarct** affecting central (1st-order) sympathetic pathways.
*Preganglionic lesion at the lateral gray horn*
- A preganglionic lesion at the lateral gray horn (T1-T2 spinal cord, **2nd-order neurons**) would cause **Horner's syndrome**.
- However, it would not explain the upper brainstem symptoms like **dysphagia**, **hoarseness**, **diplopia**, or **nystagmus**, which result from damage to cranial nerve nuclei and tracts within the medulla, not the spinal cord.
Question 10: A 45-year-old woman comes to the physician because of progressive difficulty swallowing solids and liquids over the past 4 months. She has lost 4 kg (9 lb) during this period. There is no history of serious illness. She emigrated to the US from Panama 7 years ago. She does not smoke cigarettes or drink alcohol. Cardiopulmonary examination shows a systolic murmur and an S3 gallop. A barium radiograph of the chest is shown. Histopathologic examination of the esophageal wall is most likely to show which of the following?
A. Presence of intranuclear basophilic inclusions
B. Atrophy of esophageal smooth muscle cells
C. Infiltration of eosinophils in the epithelium
D. Presence of metaplastic columnar epithelium
E. Absence of myenteric plexus neurons (Correct Answer)
Explanation: ***Absence of myenteric plexus neurons***
- This finding is pathognomonic for **Chagas disease** (American trypanosomiasis), caused by *Trypanosoma cruzi*, endemic to Central and South America including Panama.
- The parasite destroys the **myenteric (Auerbach's) plexus neurons** in the esophageal wall, disrupting normal peristalsis and leading to **megaesophagus**.
- This results in **progressive dysphagia for both solids and liquids** and weight loss, as seen in this patient.
- The **cardiac findings** (systolic murmur and S3 gallop) indicate associated **chagasic cardiomyopathy**, another manifestation of chronic Chagas disease.
*Presence of intranuclear basophilic inclusions*
- Suggestive of **cytomegalovirus (CMV) esophagitis**, typically seen in immunocompromised patients (HIV/AIDS, transplant recipients).
- This patient has no immunocompromised state, and CMV does not cause the cardiac manifestations or chronic megaesophagus seen here.
*Atrophy of esophageal smooth muscle cells*
- Not characteristic of Chagas disease or achalasia; these conditions typically show **smooth muscle hypertrophy** due to chronic obstruction.
- Muscle atrophy would not explain the dysphagia, megaesophagus, or cardiac findings.
*Infiltration of eosinophils in the epithelium*
- Indicates **eosinophilic esophagitis**, an allergic condition usually presenting with food impaction and dysphagia mainly for solids.
- Would not explain the cardiac manifestations or the epidemiological connection to Panama.
*Presence of metaplastic columnar epithelium*
- Represents **Barrett's esophagus**, a complication of chronic gastroesophageal reflux disease (GERD).
- The patient's presentation with dysphagia for both solids and liquids, cardiac disease, and megaesophagus on barium study points to a **motility disorder** (Chagas disease), not reflux disease.
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