Ptosis is a common feature of which condition?

• A. Myasthenia gravis
• B. Hyperthyroidism
• C. Parkinson's disease
• D. Multiple sclerosis

Answer: (A)

Ptosis reflects fatigable weakness of the eyelid elevator caused by autoimmune destruction or blockade of acetylcholine receptors at the neuromuscular junction in myasthenia gravis. Because the affected muscles tire with use, the lid droops more with activity and improves after rest or with acetylcholinesterase inhibitors. This fluctuating ocular weakness, often with diplopia as well, is a hallmark presentation of MG. Other conditions can involve the eyes, but they don’t typically produce the same pattern of fatigable eyelid weakness: hyperthyroidism tends to cause lid retraction and eyelid edema with exophthalmos, Parkinson’s disease can cause a mask-like face with reduced blinking and mild ptosis, and multiple sclerosis may affect cranial nerves but ptosis isn’t the defining feature.