Question

History: Sarah is a 28-year-old gymnastics instructor who went to her doctor, presenting complaints of progressively worsening muscle weakness in her face that comes and goes 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 complains of double vision occurring late in the evening, particularly after reading for a few minutes. In the past few weeks, she is also noticing muscle weakness in her upper arms, remarking it has been difficult to "spot" her gymnasts during acrobatic moves.

Examination: 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.

Treatment: Sarah was treated with pyridostigmine bromide, which is a long-acting anticholinesterase drug, and was also started on prednisone, a corticosteroid drug. She also must undergo 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.

1. Why is Sarah experiencing difficulty chewing and double vision?

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

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

4. Why are nausea, abdominal cramps, diarrhea, and excessive salivation all side effects of the anticholinesterase drug she is taking? Why is atropine beneficial in treating these gastrointestinal side effects?

5. How will the corticosteroid prednisone benefit the patient? How about the plasmapheresis when her symptoms become especially severe?

Answer 1