Which condition is characterized by muscle weakness and is caused by an autoimmune response?

Myasthenia gravis is characterized by muscle weakness due to an autoimmune response where the body produces antibodies that attack the acetylcholine receptors at the neuromuscular junction. This impairs communication between nerves and muscles, leading to symptoms such as muscle fatigue and weakness that typically worsen with activity and improve with rest.

The condition specifically affects skeletal muscles, which are responsible for voluntary movements, such as those in the face, arms, and legs. The hallmark of myasthenia gravis is the fluctuating nature of muscle strength, which is exacerbated by exertion and can often lead to significant functional impairments in daily activities.

The other conditions mentioned have different underlying mechanisms or symptoms. For example, multiple sclerosis primarily affects the central nervous system and involves demyelination, while Guillain-Barré syndrome involves acute peripheral nerve demyelination, often following an infection. Pernicious anemia, on the other hand, is related to vitamin B12 deficiency and primarily affects red blood cell production, rather than muscle strength directly through an autoimmune process.