What muscle groups are mostly affected by Myasthenia Gravis (MG)?

From the Guidelines

Myasthenia gravis primarily affects the voluntary muscles controlled by the cranial nerves, with ocular muscles being most commonly affected, as stated in the most recent study 1 from 2024. The muscle groups mostly affected by Myasthenia Gravis (MG) include:

• Ocular muscles, which are affected in about 90% of patients, causing drooping eyelids (ptosis) and double vision (diplopia) 1
• Facial muscles, which are the second most affected group, leading to a characteristic "myasthenic snarl" when smiling
• Bulbar muscles controlling speech and swallowing, which are frequently involved, causing dysarthria (slurred speech) and dysphagia (swallowing difficulties)
• Neck and limb muscles, which can also be affected, with proximal muscles (shoulders, hips) typically more impacted than distal ones
• Respiratory muscles, which may become involved in severe cases, potentially leading to myasthenic crisis requiring ventilatory support This pattern of muscle involvement occurs because myasthenia gravis is an autoimmune disorder where antibodies attack acetylcholine receptors at the neuromuscular junction, disrupting nerve signals to muscles, as explained in 1. The preferential involvement of certain muscle groups relates to differences in neuromuscular junction structure and acetylcholine receptor density across different muscle types, as discussed in 1 and 1. It is essential to recognize the disorder to initiate appropriate workup and referral to other subspecialties, including neurology, as emphasized in 1 and 1. Proper medical and surgical treatment, including the use of pyridostigmine, corticosteroids, and thymectomy, can help manage the symptoms and improve the quality of life for patients with myasthenia gravis, as outlined in 1 and 1.

From the Research

Muscle Groups Affected by Myasthenia Gravis (MG)

The muscle groups mostly affected by Myasthenia Gravis (MG) include:

• Ocular muscles, leading to symptoms such as asymmetric ptosis and binocular diplopia 2, 3, 4, 5
• Facial muscles 6, 3
• Oropharyngeal muscles 2, 6, 3
• Axial muscles 6, 5
• Limb muscles, including leg muscles 2, 6, 5
• Bulbar muscles, which can lead to respiratory problems 2, 3, 4, 5

Characteristics of Muscle Weakness in MG

The muscle weakness in MG is characterized by:

• Fluctuating weakness that worsens with use and improves with rest 2, 6, 3, 4, 5
• Fatigable weakness, which becomes worse with intercurrent episodes of infection, fever, and physical or emotional exhaustion 3
• Exercise-induced fatigue and sometimes manifest muscle weakness 4