A 60-Year-Old Man Comes to the Office Due to Fatigue

question 844

Multiple Choice

A 60-year-old man comes to the office due to fatigue and muscle weakness in his extremities.  The weakness has gotten progressively worse over the past few months.  He has also lost 7 kg (15.4 lb) during the last 3 months.  He has no other medical conditions.  The patient smokes 2 packs of cigarettes daily and consumes alcohol occasionally.  On examination, he has difficulty getting out of the chair to sit on the examining table.  Muscle strength is 3/5 in the proximal muscle groups symmetrically and is not improved by repeated muscle contractions.  Reflexes are 2+ bilaterally.  No sensory abnormality is present.  There are erythematous patches and violaceous papules involving the dorsum of his fingers.  Chest x-ray reveals an ill-defined mass in the right lower lobe.  The patient's muscle weakness is most likely due to a pathologic process at which of the following?

• A)Muscle fibers
• B)Peripheral nerves
• C)Postsynaptic membrane
• D)Presynaptic membrane
• E)Spinal cord

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Definitions:

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