Reference no: EM133603685
Assignment:
Chief Complaint: A 26-year-old woman with muscle weakness in the face.
History: Jill Rothman, a 26-year-old gymnastics instructor, presents 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.
Jill's doctor ordered an EMG test to be performed. Electromyography (EMG) measures muscle response or electrical activity in response to a nerve's stimulation of the muscle. The test is used to help detect neuromuscular abnormalities. During the test, small needles (also called electrodes) are inserted through the skin into the muscle.
EMG measures the electrical activity of muscle during rest, slight contraction, and forceful contraction. Muscle tissue does not normally produce electrical signals during rest. When an electrode is inserted, a brief period of activity can be detected, but after that, no signal should be present.
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 (also called an anticholinesterase).
For more information about EMG testing:
Blood testing revealed high levels of an anti-acetylcholine 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 was also 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. Atropine is an antimotility drug that relaxes muscles.
In addition, Jill underwent occasional plasmapheresis when her symptoms became especially severe. Plasmapheresis is a process where antibodies are filtered out of blood.
Questions:
1. Why is this young woman having trouble chewing and double vision?
2. What is the function of acetylcholine in muscle contraction?
3. What is the function of the enzyme acetylcholinesterase?
4. How are the anti-acetylcholine antibodies interfering with her normal skeletal muscle activity?
5. How do the anticholinesterase drugs act to improve Jill's skeletal muscle function?
6. Why is atropine beneficial in treating the gastrointestinal side effects mentioned in the question above?
7. Why does repetitive nerve stimulation result in decreased amplitude of muscle contractions?
8. How will the corticosteroid prednisone benefit this patient?
9. Why must Jill undergo plasmapheresis when her symptoms become especially severe?
10. Jill's doctor advises her that she is at increased risk for respiratory failure. Explain why this is so.