Neuromuscular Disorders — MCQs

10 questions

To which muscle relaxant are patients with myasthenia gravis (MG) most sensitive?

A middle-aged woman suffers from weakness of her ocular and facial muscles, which worsens with repeated use. She has antibodies to acetylcholine receptors in her serum. The likely diagnosis is:

Which of the following is characterized by denervation atrophy of the muscles?

Myasthenia gravis is a disorder of:

Which of the following is not a typical symptom of Duchenne Muscular Dystrophy (DMD)?

A 70 kg young athlete was planned for surgery. During anesthesia, vecuronium was not available, so repeated doses of succinylcholine were given intermittently up to 640 mg. During recovery, the patient was not able to spontaneously respire and move limbs. What is the cause?

Which inhalational agent increases intracranial pressure most significantly?

The commonly used muscle relaxant with quickest onset of action and spontaneous recovery is :

Q9Medium

Which is the inhalation agent of choice in a patient with raised intracranial pressure?

Q10Medium

Intracranial pressure (ICP) is raised due to:

Neuromuscular Disorders Indian Medical PG Practice Questions and MCQs

Question 1: To which muscle relaxant are patients with myasthenia gravis (MG) most sensitive?

A. Gallamine (Correct Answer)
B. Atracurium
C. Scoline
D. Decamethonium

Explanation: ***Gallamine*** - Patients with **myasthenia gravis (MG)** have fewer functional **acetylcholine receptors** at the neuromuscular junction, making them **extremely sensitive** to **non-depolarizing neuromuscular blockers** [1]. - Gallamine is a **long-acting non-depolarizing agent** with **no spontaneous degradation pathway**, relying entirely on renal elimination, which makes the **prolonged neuromuscular blockade particularly dangerous** in MG patients. - MG patients require **markedly reduced doses** (up to 50% reduction) of non-depolarizing agents, and standard doses can lead to **severe, prolonged paralysis** and respiratory failure. - Among non-depolarizing agents, **longer-acting drugs like gallamine** pose the greatest clinical risk due to extended blockade duration [2]. *Atracurium* - While atracurium is also a **non-depolarizing blocker** and MG patients are sensitive to it, it has a **more predictable, shorter duration** due to its unique **Hofmann elimination** (spontaneous degradation at physiological pH and temperature). - This spontaneous breakdown makes it **relatively safer** in MG patients compared to longer-acting agents that depend on hepatic or renal elimination. - Still requires dose reduction in MG, but with better safety profile. *Scoline (Succinylcholine)* - Scoline is a **depolarizing neuromuscular blocker** that acts differently from non-depolarizing agents [3]. - MG patients typically show **resistance** to succinylcholine initially (require **larger doses**) because they have fewer receptors to depolarize. - This is **opposite to the hypersensitivity** seen with non-depolarizing blockers, making this option incorrect for "most sensitive." *Decamethonium* - Decamethonium is another **depolarizing blocker**, now obsolete in clinical practice. - Like succinylcholine, MG patients show **initial resistance** rather than hypersensitivity, requiring higher doses for effect [4]. - This contradicts the concept of increased sensitivity.

Question 2: A middle-aged woman suffers from weakness of her ocular and facial muscles, which worsens with repeated use. She has antibodies to acetylcholine receptors in her serum. The likely diagnosis is:

A. Lambert-Eaton myasthenic syndrome
B. Parkinson's Disease
C. Myasthenia gravis (Correct Answer)
D. Botulism

Explanation: ***Myasthenia gravis*** - The classic presentation of **ocular** and **facial muscle weakness** that **worsens with repeated use** (fatigability) is highly characteristic of myasthenia gravis [1]. - The presence of **antibodies to acetylcholine receptors** in the serum is the hallmark diagnostic finding for myasthenia gravis, confirming the autoimmune etiology [1], [2]. *Lambert-Eaton myasthenic syndrome* - This syndrome typically presents with **proximal muscle weakness**, particularly of the **lower limbs**, and often **improves with repeated use** (opposite of myasthenia gravis) [3]. - It is often associated with **small cell lung cancer** and involves antibodies against **presynaptic voltage-gated calcium channels**, not acetylcholine receptors [3]. *Parkinson's Disease* - Parkinson's disease is a **neurodegenerative disorder** affecting the **basal ganglia**, leading to motor symptoms such as **tremor at rest**, **rigidity**, **bradykinesia**, and **postural instability**. - It does not involve muscle weakness that worsens with repeated use, nor is it characterized by autoantibodies to acetylcholine receptors. *Botulism* - Botulism is caused by a **neurotoxin** that **inhibits acetylcholine release** at the neuromuscular junction, leading to a **descending flaccid paralysis**. - While it causes muscle weakness, it does not typically present with the characteristic ocular and facial muscle involvement that worsens with repeated use in the same way as myasthenia gravis, and it is not an autoimmune condition with acetylcholine receptor antibodies.

Question 3: Which of the following is characterized by denervation atrophy of the muscles?

A. Werdnig-Hoffman disease (Correct Answer)
B. Carnitine palmityl transferase deficiency
C. McArdle disease
D. Pompe disease

Explanation: ***Werdnig-Hoffman disease*** - This is a severe form of **spinal muscular atrophy (SMA)**, characterized by the degeneration of **anterior horn cells** in the spinal cord [1]. - The loss of motor neurons leads to **denervation atrophy** of skeletal muscles, resulting in profound weakness and hypotonia [1], [2]. *Carnitine palmityl transferase deficiency* - This is a **fatty acid oxidation disorder** that primarily affects muscle energy metabolism. - It causes muscle pain, weakness, and **rhabdomyolysis** during sustained exercise, but not denervation atrophy. *McArdle disease* - Also known as **glycogen storage disease type V**, this condition is caused by a deficiency in **myophosphorylase**. - It results in exercise intolerance, muscle cramps, and myoglobinuria, but the muscle damage is metabolic, not from denervation. *Pompe disease* - This is a **lysosomal storage disorder** caused by a deficiency of **acid alpha-glucosidase (GAA)**. - It leads to the accumulation of glycogen in lysosomes, causing muscle weakness, cardiomyopathy, and respiratory failure, but the muscle pathology is due to lysosomal dysfunction, not denervation. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Peripheral Nerves and Skeletal Muscles, pp. 1239-1240, 1247-1248. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Manifestations Of Central And Peripheral Nervous System Disease, pp. 730-731.

Question 4: Myasthenia gravis is a disorder of:

A. Spinal cord
B. Motor neuron
C. Neuromuscular junction (Correct Answer)
D. Peripheral nerve

Explanation: Neuromuscular junction - **Myasthenia gravis** is an **autoimmune disorder** where antibodies attack **acetylcholine receptors** at the **neuromuscular junction**, impairing nerve-to-muscle communication [1], [2]. - This leads to characteristic **muscle weakness** that worsens with activity and improves with rest [2]. *Spinal cord* - Disorders of the **spinal cord** typically involve sensory, motor, and autonomic deficits below the level of the lesion, often characterized by **spasticity** and **hyperreflexia**. - **Myasthenia gravis** does not directly affect the spinal cord, and its symptoms are distinct from spinal cord pathologies. *Motor neuron* - **Motor neuron diseases** (e.g., **ALS**) primarily affect the motor neurons in the brain and spinal cord, leading to progressive **muscle atrophy**, **fasciculations**, and **weakness** due to **denervation**. - Myasthenia gravis does not involve motor neuron degeneration; the neurons themselves are healthy. *Peripheral nerve* - **Peripheral nerve disorders** (e.g., **Guillain-Barré syndrome**) involve damage to nerves outside the brain and spinal cord, causing sensory changes (numbness, tingling), muscle weakness, and often **diminished reflexes**. - While myasthenia gravis causes weakness, it is due to a problem at the junction between the nerve and muscle, not within the nerve itself.

Question 5: Which of the following is not a typical symptom of Duchenne Muscular Dystrophy (DMD)?

A. Muscle pseudo hypertrophy
B. Muscle weakness
C. Tenderness in muscles (Correct Answer)
D. Cardiomyopathy
E. Gower's sign

Explanation: ***Tenderness in muscles*** - **Muscle tenderness** and pain are **not typical primary symptoms** of Duchenne Muscular Dystrophy (DMD); the disease is characterized by progressive muscle weakness without significant pain. - While some discomfort might arise from muscle spasms or joint issues, widespread tenderness is characteristic of inflammatory conditions, not DMD. *Muscle pseudo hypertrophy* - **Pseudohypertrophy**, particularly in the calves, is a **hallmark sign** of DMD, caused by the replacement of muscle tissue with fat and connective tissue, making the muscles appear larger but weaker. - This symptom reflects the underlying muscle degeneration in DMD. *Muscle weakness* - **Progressive muscle weakness** is the defining characteristic of DMD, typically starting in the proximal muscles and leading to significant functional impairment. - This weakness is due to the lack of **dystrophin**, which is crucial for muscle fiber integrity. *Cardiomyopathy* - **Cardiomyopathy** is a **common and serious complication** of DMD, affecting nearly all patients by adolescence or early adulthood due to the absence of dystrophin in cardiac muscle. - It often manifests as **dilated cardiomyopathy**, contributing significantly to morbidity and mortality. *Gower's sign* - **Gower's sign** is a **classic clinical manifestation** of DMD, where the child uses their hands to "walk up" their legs when rising from the floor due to proximal muscle weakness. - This sign typically appears early in the disease course and is a key diagnostic indicator.

Question 6: A 70 kg young athlete was planned for surgery. During anesthesia, vecuronium was not available, so repeated doses of succinylcholine were given intermittently up to 640 mg. During recovery, the patient was not able to spontaneously respire and move limbs. What is the cause?

A. Phase II blockade (Correct Answer)
B. Muscle weakness due to repeated fasciculations
C. Undiagnosed muscular dystrophy
D. Pseudocholinesterase deficiency

Explanation: **Phase II blockade** - Prolonged administration of **succinylcholine** (> 30-60 minutes or high cumulative doses) can lead to a shift from Phase I to **Phase II block**. - In Phase II block, the neuromuscular junction exhibits characteristics similar to a **nondepolarizing block**, including fade on train-of-four stimulation and post-tetanic potentiation, leading to prolonged paralysis. *Muscle weakness due to repeated fasciculations* - While succinylcholine initially causes **fasciculations** due to depolarization, prolonged paralysis is not directly explained by muscle weakness from repeated fasciculations alone. - Fasciculations are a transient early effect and do not account for the sustained paralysis seen with high-dose, repeated administration. *Undiagnosed muscular dystrophy* - While certain **neuromuscular disorders** can alter response to muscle relaxants, there is no information in the scenario to suggest pre-existing muscular dystrophy. - Administering a large amount of succinylcholine accounts for the prolonged paralysis without needing to invoke an undiagnosed condition. *Pseudocholinesterase deficiency* - A deficiency in **pseudocholinesterase** would lead to a prolonged initial Phase I block with a typical dose of succinylcholine due to impaired metabolism. - However, the scenario describes **repeated doses** adding up to a very high cumulative amount (640 mg), pushing the patient into a Phase II block even if pseudocholinesterase levels were normal.

Question 7: Which inhalational agent increases intracranial pressure most significantly?

A. Halothane (Correct Answer)
B. Sevoflurane
C. Isoflurane
D. Desflurane

Explanation: ***Halothane*** - **Halothane** causes a greater increase in **cerebral blood flow** and thus **intracranial pressure (ICP)** compared to newer volatile anesthetics due to its more potent cerebral vasodilation. - Its use has largely declined due to concerns about its effects on ICP and potential for **hepatotoxicity**. *Sevoflurane* - While sevoflurane can cause **cerebral vasodilation** and increase ICP, its effect is generally less pronounced than halothane, especially when normocapnia is maintained. - It is often favored in neuroanesthesia due to its rapid onset and offset, allowing for quicker adjustments in anesthetic depth. *Isoflurane* - Isoflurane causes less cerebral vasodilation and a smaller increase in ICP compared to halothane, particularly at lower concentrations. - It maintains **cerebral vascular autoregulation** better than halothane, helping to preserve a more stable ICP. *Desflurane* - Desflurane also causes cerebral vasodilation and can increase ICP, but its effect is typically less significant than halothane. - Rapid increases in desflurane concentration can lead to sympathetic stimulation and transient increases in blood pressure, which can indirectly affect ICP.

Question 8: The commonly used muscle relaxant with quickest onset of action and spontaneous recovery is :

A. Vecuronium
B. Rocuronium
C. Suxamethonium (Correct Answer)
D. Atracurium

Explanation: ***Suxamethonium*** - Suxamethonium (succinylcholine) is a **depolarizing neuromuscular blocker** with the most rapid onset of action (30-60 seconds) due to its unique mechanism. - Its short duration of action and **spontaneous recovery** are due to its rapid hydrolysis by **plasma pseudocholinesterase**, making it ideal for rapid sequence intubation. *Vecuronium* - Vecuronium is an **intermediate-duration non-depolarizing neuromuscular blocker** with an onset of action typically around 3-5 minutes, which is slower than suxamethonium. - It does not undergo spontaneous recovery as rapidly as suxamethonium and often requires administration of a **reversal agent**. *Rocuronium* - Rocuronium is a **non-depolarizing neuromuscular blocker** known for its relatively rapid onset of action (60-90 seconds) among non-depolarizing agents, but it is still slower than suxamethonium. - While it can be reversed quickly with sugammadex, its **spontaneous recovery** is much slower than suxamethonium. *Atracurium* - Atracurium is an **intermediate-duration non-depolarizing neuromuscular blocker** with an onset of action (3-5 minutes) that is slower than suxamethonium. - Its metabolism involves **Hofmann elimination** and ester hydrolysis, providing a degree of organ-independent elimination, but its recovery is not as rapid or spontaneous as suxamethonium.

Question 9: Which is the inhalation agent of choice in a patient with raised intracranial pressure?

A. Isoflurane (Correct Answer)
B. Enflurane
C. Sevoflurane
D. Halothane

Explanation: **Explanation:** The primary goal in neuroanesthesia for patients with raised intracranial pressure (ICP) is to maintain cerebral perfusion pressure (CPP) while preventing further increases in ICP. **Why Isoflurane is the Correct Answer:** Isoflurane is considered the volatile anesthetic of choice for neurosurgery because it provides a favorable balance between cerebral metabolic rate (CMRO2) reduction and cerebral vasodilation. At doses below 1 MAC, Isoflurane significantly reduces CMRO2 (neuroprotection) while causing minimal cerebral vasodilation. Any potential increase in ICP due to vasodilation can be easily blunted by inducing **mild hypocapnia (hyperventilation)**. Furthermore, it preserves cerebral autoregulation better than older agents. **Analysis of Incorrect Options:** * **Halothane:** This is the most potent cerebral vasodilator among all inhalational agents. It significantly increases cerebral blood volume and ICP, making it contraindicated in patients with space-occupying lesions. * **Enflurane:** It is avoided in neurosurgery because it can induce **seizure-like activity** on EEG, especially under conditions of hypocapnia, which increases cerebral oxygen demand. * **Sevoflurane:** While also used in neuroanesthesia, it is generally considered second to Isoflurane because, at higher concentrations (>1.5 MAC), it may impair cerebral autoregulation more than Isoflurane. **High-Yield Clinical Pearls for NEET-PG:** * **Order of Vasodilation (ICP Increase):** Halothane > Enflurane > Isoflurane = Sevoflurane = Desflurane. * **Order of CMRO2 Suppression:** Isoflurane is the most potent at suppressing metabolic rate. * **Intravenous Agent of Choice:** **Propofol** is the preferred IV induction agent as it reduces both CMRO2 and ICP (cerebral vasoconstrictor). * **Nitrous Oxide (N2O):** Should be avoided as it increases ICP and can expand a pneumocephalus.

Question 10: Intracranial pressure (ICP) is raised due to:

A. Ketamine (Correct Answer)
B. Scoline
C. Halothane
D. Ether

Explanation: ### Explanation **Correct Answer: A. Ketamine** **Mechanism of Action:** Ketamine is a dissociative anesthetic that acts as an NMDA receptor antagonist. Unlike most other induction agents, Ketamine is a potent **cerebral vasodilator**. It increases Cerebral Blood Flow (CBF) and Cerebral Metabolic Rate of Oxygen ($CMRO_2$), which leads to a significant **increase in Intracranial Pressure (ICP)**. Consequently, it is generally contraindicated in patients with space-occupying lesions, head injuries, or intracranial hypertension. **Analysis of Other Options:** * **B. Scoline (Succinylcholine):** While Succinylcholine can cause a transient, mild increase in ICP (likely due to muscle fasciculations and increased CVP), it is **not** the primary answer in this context. In modern neuroanesthesia, its benefits for rapid sequence induction often outweigh this minor risk, and the effect can be blunted with defasciculating doses of non-depolarizers. * **C. Halothane:** Halothane is a potent vasodilator and can increase ICP; however, in the hierarchy of "ICP-elevating drugs" for exam purposes, Ketamine is the classic "high-yield" answer due to its profound effect on cerebral hemodynamics. * **D. Ether:** While Ether causes some vasodilation, it is obsolete in modern practice and less potent in its ICP-elevating effects compared to Ketamine. **High-Yield Clinical Pearls for NEET-PG:** * **The "Neuro-Friendly" Induction Agent:** **Thiopentone** (and Propofol) are the drugs of choice for neurosurgery as they decrease $CMRO_2$, CBF, and ICP (cerebral protection). * **Exceptions for Ketamine:** Recent studies suggest that if a patient is well-ventilated (normocapnia maintained), the ICP increase from Ketamine may be minimal, but for MCQ purposes, **Ketamine = Increased ICP**. * **Inhalational Agents:** All volatile anesthetics cause vasodilation at >1 MAC, but **Sevoflurane** is preferred over Halothane in neurosurgery because it has the least effect on cerebral autoregulation.

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