Myasthenia gravis
 

Right ptosis due to myasthenia gravis showing fatiguability of the right lid on sustained upgaze   This is also called the Simpson test in which fatigure is observed on sustained lid and eye elevation. a

There is a right partial ptosis. The pupils are equal in size. There may be limitation of ocular movement in any combination. The vertical muscles tend to be affected most. The limitation is variable and does not appear to correspond to any nerve palsy. On sustained upgaze, the right upper lid shows increased ptosis. Perform the following: Cogan's lid twitch sign = get the patient to rapidly refixate their eye from downgaze to the primary position, the sign is positive if there is overshooting of the upper lid before settling down to the ptotic position  Animated pitcutre of a patient with right Cogan's twitch sign on rapid upgaze. Note the overshooting of the lid before settling down to the original ptotic level.   look for other signs of myasthenia gravis: thoracic scar from thymomectomy and weak voice.

Questions:

1. During the Tensilon test, a patient collapses. How would you manage the patient?

answer
During the Tensilon test, it is important to have the resuscitation equipment at hand. The patient's blood pressure and pulse should be monitored.  The most likely cause of collapse is bradycardia and atropine should be given intravenously through a pre-placed venflon.

2. How would you perform an ice pack test?

answer
Ice is applied over the ptotic eye for two minutes. In patient with myasthenia gravis, the ptosis improves.

3. How are the differences between  myasthenia gravis and Lambert-Eaton's syndrome?

answer
Lambert-Eaton's syndrome like myasthenia gravis affects the neuromuscular junctions, however, Lambert-Eaton's syndrome:
rarely affects the eyes
there is reduced tendon reflexes (normal in myasthenia gravis)
power is improved following exercises
associated with underlying carcinoma especially the oat cell carcinoma of the lungs

Biochemically, the antibodies seen in Lamber-Eaton's syndrome target the pre-synaptic neurone receptor whereas those in myasthenia gravis affects the post-synaptic acetylcholine receptors.

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