ABEM Neuromuscular Disorders & Diagnostic Criteria — Questions and Answers

Question 1: Which of the following is a hallmark symptom of myasthenia gravis?

Constant muscle cramps
Fluctuating muscle weakness (Correct answer)
Chronic joint pain
Sensory neuropathy

Correct answer: Fluctuating muscle weakness

Myasthenia gravis is an autoimmune disorder characterized by fluctuating muscle weakness that worsens with activity and improves with rest. This hallmark symptom is due to antibodies blocking or destroying acetylcholine receptors at the neuromuscular junction, impairing signal transmission between nerves and muscles. The variability in weakness throughout the day or with exertion is highly characteristic.

Question 2: What test is commonly used to diagnose Guillain-Barré Syndrome?

MRI scan
Blood glucose test
Nerve conduction studies (Correct answer)
X-ray

Correct answer: Nerve conduction studies

Guillain-Barré Syndrome (GBS) is an acute inflammatory demyelinating polyneuropathy affecting the peripheral nervous system. Nerve conduction studies (NCS) are critical for diagnosing GBS by revealing characteristic findings such as slowed conduction velocities, prolonged latencies, and conduction blocks. These findings indicate widespread demyelination of peripheral nerves, which is the pathological basis of GBS.

Question 3: What is a common diagnostic feature of amyotrophic lateral sclerosis (ALS)?

Only sensory symptoms
Combined upper and lower motor neuron signs (Correct answer)
Improved reflexes
Erythematous rash

Correct answer: Combined upper and lower motor neuron signs

Amyotrophic Lateral Sclerosis (ALS) is a progressive neurodegenerative disease that uniquely affects both upper motor neurons (in the brain and spinal cord) and lower motor neurons (in the brainstem and spinal cord). This combination leads to a distinct clinical presentation of both spasticity, hyperreflexia (upper motor neuron signs), and muscle weakness, atrophy, and fasciculations (lower motor neuron signs). This dual involvement is a key diagnostic feature.

Question 4: Which neuromuscular disorder typically shows a decremental response on repetitive nerve stimulation?

Peripheral neuropathy
Muscular dystrophy
Myasthenia gravis (Correct answer)
Multiple sclerosis

Correct answer: Myasthenia gravis

Myasthenia gravis is characterized by a decremental response on repetitive nerve stimulation, meaning the amplitude of the muscle action potential decreases with successive stimulations. This occurs because the limited number of available acetylcholine receptors at the neuromuscular junction become progressively saturated or desensitized. This impaired neuromuscular transmission leads to the observed decrement.

Question 5: What condition is primarily characterized by muscle inflammation and weakness?

Charcot-Marie-Tooth disease
Polymyositis (Correct answer)
Guillain-Barré Syndrome
Parkinson’s disease

Correct answer: Polymyositis

Polymyositis is an inflammatory myopathy primarily characterized by inflammation of the muscles, leading to progressive muscle weakness, particularly in the proximal muscles. This condition is distinct from neuropathies or other muscle disorders as its primary pathology involves direct inflammation within the muscle tissue itself. The inflammation causes muscle fiber damage and subsequent weakness.

Question 6: In which disorder is muscle biopsy often diagnostic?

Parkinson’s disease
Muscular dystrophy (Correct answer)
Epilepsy
Cerebral palsy

Correct answer: Muscular dystrophy

Muscle biopsy is often diagnostic for muscular dystrophies, a group of genetic disorders characterized by progressive muscle weakness and degeneration. The biopsy allows for microscopic examination of muscle tissue, revealing characteristic pathological changes like fiber necrosis, regeneration, and variations in fiber size. These findings help confirm the diagnosis and differentiate between various types of muscular dystrophy.

Question 7: What is a distinguishing clinical sign of Lambert-Eaton Myasthenic Syndrome (LEMS)?

Increasing weakness with use
Symmetrical spasticity
Improved strength with activity (Correct answer)
Seizures

Correct answer: Improved strength with activity

Lambert-Eaton Myasthenic Syndrome (LEMS) is an autoimmune disorder affecting the presynaptic nerve terminal, impairing acetylcholine release. A distinguishing clinical sign is a transient improvement in muscle strength with sustained or repeated activity, known as post-tetanic potentiation. This phenomenon occurs as repeated stimulation facilitates calcium influx and neurotransmitter release, temporarily overcoming the presynaptic defect.

Question 8: Which of these is a hereditary neuromuscular disorder?

ALS
Guillain-Barré Syndrome
Charcot-Marie-Tooth disease (Correct answer)
Myasthenia gravis

Correct answer: Charcot-Marie-Tooth disease

Charcot-Marie-Tooth (CMT) disease is a group of inherited neurological disorders that affect the peripheral nerves. It is one of the most common hereditary neuromuscular disorders, leading to progressive muscle weakness and sensory loss, primarily in the feet, lower legs, hands, and forearms. Its genetic basis and progressive nature distinguish it as a hereditary condition.

Question 9: Which disorder presents with facial and distal limb weakness, especially after exertion?

Polymyositis
Myotonic dystrophy (Correct answer)
ALS
Multiple sclerosis

Correct answer: Myotonic dystrophy

Myotonic dystrophy is a hereditary multi-system disorder characterized by myotonia (delayed muscle relaxation) and progressive muscle weakness. It commonly presents with facial weakness, distal limb weakness, and often worsens after exertion, alongside other systemic features like cataracts and cardiac conduction defects. The combination of myotonia and specific weakness patterns is characteristic.

ABEM Neuromuscular Disorders & Diagnostic Criteria

Which of the following is a hallmark symptom of myasthenia gravis?