Case History 7: Muscle Weakness

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Chief Complaint: A 26-year-old woman with muscle weakness in the face.

History: Jill Rothman, a 26-year-old gymnastics instructor, presents with complaints of muscle weakness in her face that comes and goes, but has been getting worse over the past two months. Most notably, she complains that her "jaw gets tired" as she chews and that swallowing has become difficult. She also notes diplopia ("double vision") which seems to come on late in the evening, particularly after reading for a few minutes. At work, it has become increasingly difficult to "spot" her gymnasts during acrobatic moves because of upper arm weakness.

On physical examination, she has notable ptosis ("drooping") of both eyelids after repeated blinking exercises. When smiling, she appears to be snarling. Electromyographic testing revealed progressive weakness and decreased amplitude of contraction of the distal arm muscles upon repeated mild shocks (5 shocks per second) of the ulnar and median nerves. Both her symptoms and electromyographic findings were reversed within 40 seconds of intravenous administration of edrophonium (Tensilon), an acetylcholinesterase inhibitor (i.e. an "anticholinesterase"). Blood testing revealed high levels of an anti-acetylcholine receptor antibody in her plasma, and a diagnosis of myasthenia gravis was made.

Jill was treated with pyridostigmine bromide, which is a long-acting anticholinesterase drug, and was also started on prednisone, which is a corticosteroid drug. She also underwent occasional plasmapheresis when her symptoms became especially severe. She was given a prescription of atropine as needed to reduce the nausea, abdominal cramps, diarrhea, and excessive salivation she experienced as side effects of the anticholinesterase drug.

Questions:

1. Why is this young woman experiencing difficulty chewing and double vision?

Answer

2. How are the anti-acetylcholine receptor antibodies interfering with her normal skeletal muscle activity?

Answer

3. How do the anticholinesterase drugs act to improve Jill's skeletal muscle function?

Answer

4. Why are nausea, abdominal cramps, diarrhea, and excessive salivation all side effects of the anticholinesterase drug she is taking?

Answer

5. Why is atropine beneficial in treating the gastrointestinal side effects mentioned in question #4?

Answer

6. Why does repetitive nerve stimulation result in decreased amplitude of the muscle contractions?

Answer

7. How will the corticosteroid prednisone benefit this patient?

Answer

8. Why must Jill undergo plasmapheresis when her symptoms become especially severe?

Answer

9. Jill's doctor advises her that she is at increased risk for respiratory failure. Explain why this is so.

Answer

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