Myasthenia gravis

Symptoms

• Muscle weakness, including:
  • Swallowing difficulty, frequent gagging, or choking
  • Paralysis
  • Muscles that function best after rest
  • Drooping head
  • Difficulty climbing stairs
  • Difficulty lifting objects
  • Need to use hands to rise from sitting positions
  • Difficulty talking
  • Difficulty chewing
• Vision problems:
  • Double vision
  • Difficulty maintaining steady gaze
  • Eyelid drooping

Additional symptoms that may be associated with this disease:

• Hoarseness or changing voice
• Fatigue
• Facial paralysis
• Drooling
• Breathing difficulty

Exams and Tests

Examination may be normal or may show muscle weakness that progressively worsens as the muscle is used. In many patients the eye muscles are affected first. Reflexes and sensation are normal. Weakness may affect the arms, legs, breathing or swallowing muscles, and any other muscle group.

• Repetitive stimulation (type of nerve conduction study) is more sensitive.
• Single-fiber EMG can be very sensitive.
• Acetylcholine receptor antibodies may be present in the blood.
• A Tensilon test is positive in some cases but must be interpreted carefully by an experienced doctor. Baseline muscle strength is evaluated. After Tensilon (edrophonium, a medication that blocks the action of the enzyme that breaks down the transmitter acetylcholine) is given, muscle function may improve.
• The patient may need a CT or MRI scan of the chest to look for a possible tumor in the thyroid.

References

Benatar M, Kaminski HJ. Evidence report: the medical treatment of ocular myasthenia (an evidence-based review): report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology. 2007;68(24):2144-9.

Zinman L, Ng E, Bril V. IV immunoglobulin in patients with myasthenia gravis: a randomized controlled trial. Neurology. 2007;68(11):837-41.

Goldman L ed. Cecil Texbook of Medicine, 23rd ed. Philadelphia, Pa: Saunders; 2007.