Which condition is characterized by episodic diplopia and proximal weakness that worsens with repetitive use?

The condition characterized by episodic diplopia and proximal weakness that worsens with repetitive use is myasthenia gravis. This autoimmune disorder affects the neuromuscular junction, leading to varying levels of weakness in voluntary muscles. The hallmark of myasthenia gravis is muscle fatigue, which becomes more pronounced with continued activity. This is particularly noticeable in muscles responsible for eye movements, resulting in diplopia (double vision) that tends to fluctuate throughout the day.

In myasthenia gravis, the body develops antibodies that interfere with acetylcholine receptors at the neuromuscular junction, which disrupts the communication between nerves and muscles. As a result, patients may notice their strength declines after periods of exertion and improves after rest.

Other conditions mentioned, such as multiple sclerosis and Guillain-Barre syndrome, have different underlying mechanisms and symptoms. While multiple sclerosis can cause diplopia, it does not typically present with weakness that worsens specifically with activity. Guillain-Barre syndrome generally presents with rapid, ascending weakness but is not characteristically associated with fluctuating strength related to usage. Lambert-Eaton syndrome also presents with muscle weakness, but it is often associated with autonomic dysfunction and typically improves with activity rather than worsens