What autoimmune condition involves antibodies that target voltage-gated calcium channels, resulting in proximal muscle weakness?

The autoimmune condition characterized by antibodies that target voltage-gated calcium channels, leading to proximal muscle weakness, is indeed Lambert-Eaton syndrome. This syndrome primarily affects the communication between nerves and muscles, specifically by interfering with the release of acetylcholine at the neuromuscular junction due to impaired calcium influx into the presynaptic terminal.

In Lambert-Eaton syndrome, the body's immune system produces antibodies against the voltage-gated calcium channels on the presynaptic nerve endings, which diminishes the release of acetylcholine and subsequently results in muscle weakness. Patients often experience improved strength with repeated use of muscles, which is a hallmark symptom of this condition.

Other conditions presented in the options do not specifically involve antibodies against voltage-gated calcium channels. For example, myasthenia gravis involves antibodies against the acetylcholine receptor, multiple sclerosis is characterized by demyelination, and myositis represents inflammation of the muscle itself without the specific involvement of calcium channels. Thus, the unique pathophysiological mechanism of Lambert-Eaton syndrome aligns perfectly with the symptoms described, making it the correct choice.