Amyotrophic lateral sclerosis US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Amyotrophic lateral sclerosis. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Amyotrophic lateral sclerosis US Medical PG Question 1: A 53-year-old woman comes to the physician because of a 3-year history of increasing weakness of her extremities and neck pain that is worse on coughing or sneezing. She first noticed weakness of her right upper extremity 3 years ago, which progressed to her right lower extremity 2 years ago, her left lower extremity 1 year ago, and her left upper extremity 6 months ago. She has had difficulty swallowing and speaking for the past 5 months. Vital signs are within normal limits. Examination shows an ataxic gait. Speech is dysarthritic. Muscular examination shows spasticity and muscle strength is decreased in all extremities. There is bilateral atrophy of the sternocleidomastoid and trapezius muscles. Deep tendon reflexes are 4+ bilaterally. Plantar response shows an extensor response bilaterally. Sensation is decreased below the C5 dermatome bilaterally. Which of the following is the most likely cause of this patient's symptoms?
- A. Cerebral glioblastoma multiforme
- B. Foramen magnum meningioma (Correct Answer)
- C. Cerebellar astrocytoma
- D. Amyotrophic lateral sclerosis
- E. Multiple sclerosis
Amyotrophic lateral sclerosis Explanation: ***Foramen magnum meningioma***
- Progressive **quadriparesis** in a **descending or ascending pattern**, associated with **neck pain exacerbated by coughing/sneezing**, suggests compression at the **craniocervical junction**.
- **Spasticity**, **hyperreflexia**, **bilateral extensor plantar responses**, and **sensory loss below C5** are classic signs of **upper motor neuron dysfunction** and **spinal cord compression** at this level.
*Cerebral glioblastoma multiforme*
- This typically presents with **focal neurological deficits**, **seizures**, or **symptoms of increased intracranial pressure**, rarely with progressive quadparesis and sensory level as seen.
- While it causes **upper motor neuron signs**, extensive spinal cord involvement and a clear sensory level are not characteristic.
*Cerebellar astrocytoma*
- Primarily causes **ataxia**, **dysmetria**, and other **cerebellar signs**, but does not explain the widespread spastic quadriparesis, clear sensory level, or bulbar symptoms.
- Neck pain worsened by coughing or sneezing and prominent upper motor neuron signs are not typical for this tumor.
*Amyotrophic lateral sclerosis*
- This disease affects both **upper and lower motor neurons** but typically spares sensation.
- The presence of **sensory loss below C5** and prominent **neck pain** makes ALS less likely.
*Multiple sclerosis*
- Characterized by **disseminated lesions in time and space**, often with relapsing-remitting symptoms and prominent sensory complaints, but a clear, progressive sensory level and severe neck pain are atypical.
- While it can cause **spasticity** and **ataxia**, the progressive, compressive pattern of symptoms and consistent sensory level point away from MS.
Amyotrophic lateral sclerosis US Medical PG Question 2: A 62-year-old woman is brought to the physician because of 6 months of progressive weakness in her arms and legs. During this time, she has also had difficulty swallowing and holding her head up. Examination shows pooling of oral secretions. Muscle strength and tone are decreased in the upper extremities. Deep tendon reflexes are 1+ in the right upper and lower extremities, 3+ in the left upper extremity, and 4+ in the left lower extremity. Sensation to light touch, pinprick, and vibration are intact. Which of the following is the most likely diagnosis?
- A. Guillain-Barré syndrome
- B. Amyotrophic lateral sclerosis (Correct Answer)
- C. Spinal muscular atrophy
- D. Myasthenia gravis
- E. Syringomyelia
Amyotrophic lateral sclerosis Explanation: ***Amyotrophic lateral sclerosis***
- The patient presents with a combination of **upper motor neuron (UMN)** signs (hyperreflexia at 3+ and 4+, possibly stiffness contributing to difficulty holding head up) and **lower motor neuron (LMN)** signs (progressive weakness, decreased muscle tone, pooling of oral secretions due to bulbar involvement). This coexistence is pathognomonic for **ALS**.
- The **progressive nature** of the weakness in arms and legs, encompassing both UMN and LMN features without sensory deficits, is characteristic of ALS.
*Guillain-Barré syndrome*
- Typically presents with **acute or subacute onset (days to weeks)** of ascending weakness, often post-infectious, and characteristically causes **areflexia** or severely diminished deep tendon reflexes.
- This patient's symptoms have been progressive over **6 months**, and she exhibits significantly **increased reflexes** in some limbs, which is inconsistent with GBS.
*Spinal muscular atrophy*
- This is a group of **autosomal recessive disorders** that primarily affect **lower motor neurons**, leading to progressive muscle weakness and atrophy, usually presenting in infancy or childhood.
- The patient's age of presentation (62 years old) and the presence of **upper motor neuron signs** (hyperreflexia) rule out SMA.
*Myasthenia gravis*
- Presents with **fluctuating muscle weakness** that worsens with activity and improves with rest, often affecting ocular, bulbar, and limb muscles. It does not typically cause hyperreflexia or sustained upper motor neuron signs.
- While the patient has difficulty swallowing and pooling oral secretions, the **progressive, sustained weakness** and varied deep tendon reflexes (hypo to hyper) are not typical of myasthenia gravis without specific triggers like exertion.
*Syringomyelia*
- Characterized by a **syrinx (cyst) within the spinal cord**, leading to sensory deficits (often **"cape-like" loss of pain and temperature sensation**) and weakness/atrophy due to LMN damage, usually affecting the upper extremities.
- This patient's **intact sensation** and the presence of widespread UMN signs (hyperreflexia in lower limb) make syringomyelia an unlikely diagnosis.
Amyotrophic lateral sclerosis US Medical PG Question 3: A 29-year-old man comes to the emergency department because of progressively worsening fatigue and shortness of breath for the past 2 weeks. His only medication is insulin. Examination shows elevated jugular venous distention and coarse crackles in both lungs. Despite appropriate life-saving measures, he dies. Gross examination of the heart at autopsy shows concentrically thickened myocardium and microscopic examination shows large cardiomyocytes with intracellular iron granules. Examination of the spinal cord shows atrophy of the lateral corticospinal tracts, spinocerebellar tracts, and dorsal columns. Which of the following is the most likely underlying cause of this patient's condition?
- A. CTG trinucleotide repeat expansion on chromosome 19
- B. SOD1 gene mutation on chromosome 21
- C. SMN1 gene mutation on chromosome 5
- D. GAA trinucleotide repeat expansion on chromosome 9 (Correct Answer)
- E. Dystrophin gene mutation on the X chromosome
Amyotrophic lateral sclerosis Explanation: ***GAA trinucleotide repeat expansion on chromosome 9***
- The patient's presentation with **hypertrophic cardiomyopathy** (concentrically thickened myocardium, large cardiomyocytes) and **neurological degeneration** affecting the **lateral corticospinal tracts, spinocerebellar tracts, and dorsal columns** is characteristic of **Friedreich ataxia**.
- **Friedreich ataxia** is caused by a **GAA trinucleotide repeat expansion** in the **FXN gene on chromosome 9**, leading to reduced frataxin protein and mitochondrial dysfunction.
*CTG trinucleotide repeat expansion on chromosome 19*
- This mutation is associated with **myotonic dystrophy type 1**, which presents with **myotonia**, muscle weakness, and often cardiac conduction abnormalities or dilated cardiomyopathy, but typically not hypertrophic cardiomyopathy or the specific spinal cord degeneration described.
- While cardiac involvement can occur, the neurological pattern of **spinal cord tract degeneration** and **hypertrophic cardiomyopathy** is not typical for myotonic dystrophy type 1.
*SOD1 gene mutation on chromosome 21*
- Mutations in the **SOD1 gene** are a common cause of **familial amyotrophic lateral sclerosis (ALS)**, characterized by progressive degeneration of upper and lower motor neurons.
- ALS primarily presents with muscle weakness, atrophy, and fasciculations, but does not typically involve **hypertrophic cardiomyopathy** or the specific pattern of **sensory tract degeneration** seen in this patient.
*SMN1 gene mutation on chromosome 5*
- This mutation causes **spinal muscular atrophy (SMA)**, a genetic disorder characterized by the loss of motor neurons in the spinal cord, leading to progressive muscle weakness and atrophy.
- SMA does not typically involve **hypertrophic cardiomyopathy** or the specific combination of motor and sensory tract degeneration described in the patient.
*Dystrophin gene mutation on the X chromosome*
- Mutations in the **dystrophin gene** cause **Duchenne and Becker muscular dystrophies**, which are characterized by progressive muscle weakness and **dilated cardiomyopathy**, not hypertrophic cardiomyopathy.
- While these disorders affect muscles, the specific pattern of **spinal cord tract atrophy** described is not a feature of dystrophinopathies.
Amyotrophic lateral sclerosis US Medical PG Question 4: A 49-year-old man presents to his primary care physician complaining of multiple symptoms. He states that over the past 8 months he has noticed voice changes and difficulty swallowing. The dysphagia started with just dry foods like crackers but has progressed to include smoothies and ice cream. He works as a newspaper editor and has also noticed trouble writing with his dominant hand. He is accompanied by his wife, who complains that he snores and drools in his sleep. His medical history is significant for hypertension and a bicuspid aortic valve. He takes hydrochlorothiazide. On physical examination, there is atrophy of the right hand. The patient’s speech is slow. A systolic murmur at the right upper sternal border is appreciated. Tapping of the left patellar tendon causes the patient’s left lower extremity to forcefully kick out. Stroking of the plantar aspect of the patient’s left foot causes his left toes to extend upward. Which of the following therapies is most likely to slow the progression of the patient’s symptoms?
- A. Amantadine
- B. Beta interferon
- C. Riluzole (Correct Answer)
- D. Donepezil
- E. Reserpine
Amyotrophic lateral sclerosis Explanation: ***Riluzole***
- This patient presents with symptoms highly suggestive of **amyotrophic lateral sclerosis (ALS)**, including progressive **dysphagia**, **voice changes**, **hand weakness/atrophy**, **hyperreflexia** (forceful patellar reflex), and a **positive Babinski sign** (extension of toes). **Riluzole** is the only medication shown to slightly prolong survival and slow the progression of ALS by inhibiting glutamate release.
- The patient's **snores and drools** are also consistent with bulbar involvement seen in ALS, as is the progressive dysphagia from dry foods to liquids.
*Amantadine*
- **Amantadine** is an antiviral drug primarily used to treat **influenza A** and to alleviate **dyskinesia** associated with **Parkinson's disease**.
- It has no known efficacy in slowing the progression of **ALS**.
*Beta interferon*
- **Beta interferon** is a medication used to treat **multiple sclerosis (MS)** by modulating the immune system to reduce inflammation and neuron damage.
- While MS can cause neurological symptoms, the clinical picture here with both upper and lower motor neuron signs without clear sensory deficits or relapsing-remitting course is not typical for MS, and beta interferon is not effective for **ALS**.
*Donepezil*
- **Donepezil** is a **cholinesterase inhibitor** primarily used to treat the symptoms of **Alzheimer's disease** by increasing acetylcholine levels in the brain, improving cognitive function.
- It does not address the motor neuron degeneration characteristic of **ALS**.
*Reserpine*
- **Reserpine** is an **antihypertensive and antipsychotic** drug that depletes catecholamines and serotonin from nerve endings.
- It is used to treat conditions like **hypertension and dyskinesias** (e.g., in Huntington's disease) but has no role in the management or slowing of **ALS** progression.
Amyotrophic lateral sclerosis US Medical PG Question 5: An 82-year-old comes to the physician for a routine checkup. He feels well. He has a history of hypertension, peripheral vascular disease, carotid stenosis, and mild dementia. His father had Parkinson's disease and died of a stroke at the age of 74 years. He has smoked one-half pack of cigarettes daily for 30 years but quit at the age of 50 years. He drinks alcohol in moderation. Current medications include aspirin and lisinopril. He appears healthy. His temperature is 36.9°C (98.4°F), pulse is 73/min, respirations are 12/min, and blood pressure is 142/92 mmHg. Examination shows decreased pedal pulses bilaterally. Ankle jerk and patellar reflexes are absent bilaterally. Sensation to light touch, pinprick, and proprioception is intact bilaterally. Muscle strength is 5/5 bilaterally. He describes the town he grew up in with detail but only recalls one of three words after 5 minutes. Which of the following is the most appropriate next step in management for these findings?
- A. Lumbar puncture
- B. Prescribe thiamine supplementation
- C. CT scan of the head
- D. Carbidopa-levodopa
- E. No further workup required (Correct Answer)
Amyotrophic lateral sclerosis Explanation: ***No further workup required***
- The patient's **depressed ankle and patellar reflexes** are common in **elderly patients** and can be part of normal aging, especially given his history of **peripheral vascular disease**.
- His memory impairment, specifically the inability to recall three words after 5 minutes while retaining detailed long-term memories, is consistent with his **known mild dementia** and represents expected age-related cognitive changes that do not require additional workup in an otherwise stable, well-functioning individual.
*Lumbar puncture*
- A lumbar puncture is an **invasive procedure** typically reserved for investigating suspected **meningitis**, **encephalitis**, **subarachnoid hemorrhage**, or certain **neurological disorders** not suggested by this patient's presentation.
- There are no signs of acute infection, inflammation, or rapidly progressing neurological decline to warrant an immediate lumbar puncture.
*Prescribe thiamine supplementation*
- **Thiamine supplementation** is primarily indicated for patients with suspected **Wernicke-Korsakoff syndrome** due to chronic alcohol abuse or severe malnutrition.
- This patient reports moderate alcohol use and shows no other signs of thiamine deficiency, such as **ataxia**, **ophthalmoplegia**, or **confusion** typical of Wernicke encephalopathy.
*CT scan of the head*
- A CT scan of the head is typically indicated for acute neurological changes like **stroke symptoms**, **severe headaches with focal deficits**, or to evaluate for **hydrocephalus** or **brain tumors**.
- While the patient has a history of mild dementia, his current cognitive findings are mild and stable, making an immediate CT scan unnecessary for routine follow-up in the absence of acute changes.
*Carbidopa-levodopa*
- **Carbidopa-levodopa** is a treatment for **Parkinson's disease**, characterized by specific motor symptoms like **bradykinesia**, **rigidity**, **tremor**, and **postural instability**.
- This patient does not exhibit any signs of Parkinson's disease, and his father's history of the disease does not automatically warrant treatment in an asymptomatic individual.
Amyotrophic lateral sclerosis US Medical PG Question 6: A 13-year-old girl is brought to the physician by her mother because of a 1-month history of abnormal movements of her muscles that she cannot control. She has a younger brother with cognitive disabilities and epilepsy. Examination shows frequent, brief, involuntary contractions of the muscle groups of the upper arms, legs, and face that can be triggered by touch. An EEG shows generalized epileptiform activity. A trichrome stain of a skeletal muscle biopsy specimen shows muscle fibers with peripheral red inclusions that disrupt the normal fiber contour. Which of the following is the most likely underlying mechanism of the patient's symptoms?
- A. CTG trinucleotide repeat expansion
- B. Mutation of the methyl-CpG binding protein 2 gene
- C. Truncated dystrophin protein
- D. Autoimmune endomysial destruction
- E. Defective oxidative phosphorylation (Correct Answer)
Amyotrophic lateral sclerosis Explanation: ***Defective oxidative phosphorylation***
- The constellation of **uncontrolled muscle movements (myoclonus)**, **epilepsy**, and the brother's **cognitive disabilities** strongly suggests a **mitochondrial disorder**.
- **Ragged red fibers** on trichrome stain of skeletal muscle biopsy are pathognomonic for **mitochondrial myopathies**, indicating defective oxidative phosphorylation due to abnormal mitochondrial aggregates.
*CTG trinucleotide repeat expansion*
- This is characteristic of **Myotonic Dystrophy**, which primarily presents with **myotonia** (delayed muscle relaxation), progressive muscle weakness, and often cataracts, rather than prominent myoclonus and seizures.
- While muscle weakness can occur, the specific biopsy findings and prominent myoclonus point away from this diagnosis.
*Mutation of the methyl-CpG binding protein 2 gene*
- A mutation in the **MECP2 gene** causes **Rett Syndrome**, an X-linked dominant disorder seen almost exclusively in girls.
- It involves normal development for 6-18 months followed by regression, loss of purposeful hand movements, **stereotypical hand-wringing**, and microcephaly, which are not described here.
*Truncated dystrophin protein*
- A truncated dystrophin protein causes **Duchenne Muscular Dystrophy**, an X-linked recessive disorder leading to progressive muscle weakness, **Gowers' sign**, and elevated creatine kinase.
- This condition does not typically present with myoclonus or the characteristic ragged red fibers, nor does it typically involve the sibling's intellectual disability and epilepsy in this manner.
*Autoimmune endomysial destruction*
- This mechanism is characteristic of **celiac disease**, which can have neurological symptoms like ataxia or peripheral neuropathy, but not typically the severe myoclonus, epilepsy, or muscle biopsy findings seen here.
- **Inflammatory myopathies** like polymyositis may show endomysial inflammation, but the clinical picture and specific biopsy findings (ragged red fibers) are not consistent.
Amyotrophic lateral sclerosis US Medical PG Question 7: A 57-year-old man presents to his primary care physician with a 2-month history of right upper and lower extremity weakness. He noticed the weakness when he started falling far more frequently while running errands. Since then, he has had increasing difficulty with walking and lifting objects. His past medical history is significant only for well-controlled hypertension, but he says that some members of his family have had musculoskeletal problems. His right upper extremity shows forearm atrophy and depressed reflexes while his right lower extremity is hypertonic with a positive Babinski sign. Which of the following is most likely associated with the cause of this patient's symptoms?
- A. HLA-DR2 haplotype
- B. Mutation in SOD1 (Correct Answer)
- C. Viral infection
- D. HLA-B8 haplotype
- E. Mutation in SMN1
Amyotrophic lateral sclerosis Explanation: ***Mutation in SOD1***
- The patient exhibits features of both **upper motor neuron (UMN)** and **lower motor neuron (LMN)** lesions, specifically **forearm atrophy** and depressed reflexes (LMN) alongside **hypertonicity** and a **positive Babinski sign** (UMN). This combination is characteristic of **amyotrophic lateral sclerosis (ALS)**.
- Mutations in the **superoxide dismutase 1 (SOD1)** gene are responsible for approximately 20% of familial ALS cases, aligning with the patient's report of "some members of his family have had musculoskeletal problems."
*HLA-DR2 haplotype*
- The **HLA-DR2 haplotype** is strongly associated with **multiple sclerosis (MS)**, an autoimmune demyelinating disease.
- While MS can cause UMN symptoms, it typically does not present with the pronounced LMN signs like **atrophy** and **depressed reflexes** seen in this patient.
*Viral infection*
- **Viral infections** can trigger various neurological conditions, such as **Guillain-Barré syndrome** (GBS) which causes demyelination of peripheral nerves.
- GBS primarily results in **ascending motor weakness** and **areflexia** (LMN signs), but it does not cause UMN signs like hypertonicity or a positive Babinski sign.
*HLA-B8 haplotype*
- The **HLA-B8 haplotype** is associated with several autoimmune diseases, including **myasthenia gravis** and **celiac disease**.
- While myasthenia gravis causes **muscle weakness**, it is characterized by **fluctuating weakness** that worsens with activity and improves with rest, affecting specific muscle groups, unlike the progressive UMN and LMN involvement seen here.
*Mutation in SMN1*
- A **mutation in the SMN1 gene** is the primary cause of **spinal muscular atrophy (SMA)**, a genetic disorder.
- SMA specifically leads to the death of **lower motor neurons** in the spinal cord, resulting in exclusively LMN signs such as **muscle weakness** and **atrophy**, without any UMN involvement (e.g., hypertonicity or Babinski sign).
Amyotrophic lateral sclerosis US Medical PG Question 8: A 55-year-old man is brought to the emergency department by ambulance from a long term nursing facility complaining of severe shortness of breath. He suffers from amyotrophic lateral sclerosis and lives at the nursing home full time. He has had the disease for 2 years and it has been getting harder to breath over the last month. He is placed on a rebreather mask and responds to questions while gasping for air. He denies cough or any other upper respiratory symptoms and denies a history of cardiovascular or respiratory disease. The blood pressure is 132/70 mm Hg, the heart rate is 98/min, the respiratory rate is 40/min, and the temperature is 37.6°C (99.7°F). During the physical exam, he begs to be placed in a sitting position. After he is repositioned his breathing improves a great deal. On physical examination, his respiratory movements are shallow and labored with paradoxical inward movement of his abdomen during inspiration. Auscultation of the chest reveals a lack of breath sounds in the lower lung bilaterally. At present, which of the following muscles is most important for inspiration in the patient?
- A. Muscles of anterior abdominal wall
- B. Sternocleidomastoid muscles (Correct Answer)
- C. Internal intercostal muscles
- D. Trapezius muscle
- E. External intercostal muscles
Amyotrophic lateral sclerosis Explanation: ***Sternocleidomastoid muscles***
- In advanced **amyotrophic lateral sclerosis (ALS)**, progressive motor neuron degeneration affects both the diaphragm and intercostal muscles
- The **paradoxical inward movement of the abdomen** during inspiration indicates severe diaphragmatic weakness or paralysis
- The **shallow respiratory movements** and **severe respiratory distress** (respiratory rate 40/min) suggest that both primary inspiratory muscle groups (diaphragm and external intercostals) are significantly compromised
- At this stage, **accessory muscles of inspiration**, particularly the **sternocleidomastoid muscles**, become critically important for maintaining ventilation by elevating the sternum and upper ribs
- The dramatic improvement when sitting upright (orthopnea relief) supports accessory muscle recruitment, as this position optimizes sternocleidomastoid mechanical advantage
- **Clinical pearl:** In neuromuscular respiratory failure, neck muscle recruitment (visible SCM contraction) is a key sign of impending respiratory failure requiring ventilatory support
*External intercostal muscles*
- The **external intercostal muscles** are normally primary muscles of inspiration that elevate the ribs
- However, in advanced ALS with **2 years of progressive disease** and worsening dyspnea over the past month, these muscles would also be significantly weakened by the neurodegenerative process
- The **lack of breath sounds in the lower lungs bilaterally** suggests poor chest wall expansion, indicating compromised intercostal function
- While they continue to contribute, they are insufficient to maintain adequate ventilation alone at this stage of disease
*Internal intercostal muscles*
- The **internal intercostal muscles** function primarily in **forced expiration** by depressing the ribs
- They do not play a significant role in inspiration
*Muscles of anterior abdominal wall*
- The **anterior abdominal wall muscles** (rectus abdominis, external/internal obliques, transversus abdominis) are **expiratory muscles** used in forced expiration and coughing
- The **paradoxical inward movement** of the abdomen during inspiration is a passive phenomenon resulting from diaphragmatic weakness—the negative intrathoracic pressure pulls the weakened diaphragm upward, which in turn draws the abdominal wall inward
- These muscles are not contributing to inspiration in this patient
*Trapezius muscle*
- The **trapezius** primarily functions in scapular movement and neck stabilization
- While it provides some mechanical stability for the shoulder girdle during accessory muscle breathing, it is not directly involved in rib cage elevation
- It plays a minor supportive role compared to the sternocleidomastoid in respiratory distress
Amyotrophic lateral sclerosis US Medical PG Question 9: A 46-year-old man comes to the physician because of a 2-month history of hoarseness and drooling. Initially, he had difficulty swallowing solid food, but now he has difficulty swallowing foods like oatmeal as well. During this period, he also developed weakness in both arms and has had an 8.2 kg (18 lb) weight loss. He appears ill. His vital signs are within normal limits. Examination shows tongue atrophy and pooled oral secretions. There is diffuse muscle atrophy in all extremities. Deep tendon reflexes are 3+ in all extremities. Sensation to pinprick, light touch, and vibration is intact. An esophagogastroduodenoscopy shows no abnormalities. Which of the following is the most likely cause of this patient's symptoms?
- A. Destruction of upper and lower motor neurons (Correct Answer)
- B. Autoimmune destruction of acetylcholine receptors
- C. Multiple cerebral infarctions
- D. Dilation of the central spinal canal
- E. Demyelination of peripheral nerves
Amyotrophic lateral sclerosis Explanation: ***Destruction of upper and lower motor neurons***
- This patient's presentation with **hoarseness, drooling, dysphagia, diffuse muscle atrophy**, and **hyperreflexia (3+ deep tendon reflexes)** points to both **upper motor neuron (UMN)** and **lower motor neuron (LMN)** signs.
- The combination of UMN and LMN involvement, particularly bulbar symptoms (hoarseness, drooling, dysphagia), diffuse muscle atrophy, and progressive weakness, is highly characteristic of **amyotrophic lateral sclerosis (ALS)**, which involves the progressive destruction of UMNs and LMNs.
*Autoimmune destruction of acetylcholine receptors*
- This describes **myasthenia gravis**, which typically presents with **fluctuating muscle weakness** that worsens with activity and improves with rest.
- While it can cause dysphagia and hoarseness, it usually spares deep tendon reflexes, and diffuse muscle atrophy is not a primary feature, nor are UMN signs like hyperreflexia.
*Multiple cerebral infarctions*
- Multiple cerebral infarctions, or **multi-infarct dementia**, can cause various neurological deficits depending on their location, but they rarely present with a diffuse, progressive picture of both UMN and LMN signs.
- The patient's symptoms are more consistent with a **neurodegenerative disease** rather than acute or subacute vascular events affecting widespread motor pathways in this specific, combined fashion.
*Dilation of the central spinal canal*
- This refers to **syringomyelia**, which typically causes **cape-like sensory loss** (loss of pain and temperature sensation across the shoulders and arms) due to damage to the spinothalamic tracts, often with **LMN weakness** in the upper extremities.
- It would not explain the prominent UMN signs (hyperreflexia), diffuse muscle atrophy in all extremities, or bulbar symptoms like hoarseness and drooling.
*Demyelination of peripheral nerves*
- This is characteristic of **peripheral neuropathies** such as **Guillain-Barré syndrome** or chronic inflammatory demyelinating polyneuropathy (CIDP).
- These conditions primarily cause **LMN signs** like **flaccid paralysis**, **hyporeflexia or areflexia**, and sensory loss, which is inconsistent with the prominent hyperreflexia seen in this patient.
Amyotrophic lateral sclerosis US Medical PG Question 10: In which of the following pathological states would the oxygen content of the trachea resemble the oxygen content in the affected alveoli?
- A. Emphysema
- B. Exercise
- C. Pulmonary embolism (Correct Answer)
- D. Pulmonary fibrosis
- E. Foreign body obstruction distal to the trachea
Amyotrophic lateral sclerosis Explanation: ***Pulmonary embolism***
- A pulmonary embolism blocks **blood flow** to a portion of the lung, creating **dead space ventilation** (high V/Q ratio).
- In the affected alveoli, **no blood perfusion** means no oxygen extraction occurs, so the alveolar oxygen content remains **high and similar to tracheal/inspired air**.
- This is the classic physiological state where ventilation continues but perfusion is absent, preventing gas exchange.
*Foreign body obstruction distal to the trachea*
- A complete obstruction **prevents fresh air** from reaching the affected alveoli.
- The trapped gas undergoes **resorption atelectasis**: oxygen is absorbed into capillary blood, CO2 diffuses in, and alveolar gas equilibrates with **venous blood** composition.
- Alveolar oxygen content becomes **very low**, not similar to tracheal air.
*Emphysema*
- Emphysema involves destruction of **alveolar walls** and enlargement of airspaces with impaired gas exchange.
- While V/Q mismatch occurs, oxygen is still extracted by perfusing blood.
- Alveolar oxygen content is **lower than tracheal air** due to ongoing (though inefficient) gas exchange.
*Exercise*
- During exercise, **oxygen consumption increases** dramatically with enhanced cardiac output and oxygen extraction.
- Alveolar oxygen content is **significantly lower** than tracheal air due to increased oxygen uptake by blood.
*Pulmonary fibrosis*
- Pulmonary fibrosis causes **thickening of the alveolar-capillary membrane**, impairing oxygen diffusion.
- Despite diffusion limitation, blood still perfuses the alveoli and extracts oxygen.
- Alveolar oxygen content is **lower than tracheal air**, though the A-a gradient is increased.
More Amyotrophic lateral sclerosis US Medical PG questions available in the OnCourse app. Practice MCQs, flashcards, and get detailed explanations.
