Myasthenia Gravis

Characteristics

Myasthenia refers to “muscle fatigue,” but it is more specific than general fatigue. It involves muscle weakness that varies in severity, is particularly noticeable after exercise, and improves with short rest. It affects voluntary muscles (not the heart) and is caused by a disrupted signal transmission between nerves and muscles.

Types

There are several forms of myasthenia:

1. Congenital Myasthenic Syndrome (inherited myasthenia)
2. Myasthenia Gravis with antibodies against the acetylcholine receptor or MuSK
3. Seronegative Myasthenia
4. Lambert-Eaton Myasthenic Syndrome (LEMS)

All forms, except congenital myasthenia, can occur at any point in life and are caused by an immune system disorder. This explains why patients with myasthenia often have other autoimmune diseases. Congenital myasthenia is usually hereditary. The predisposition for immune system dysregulation can also be inherited, leading to higher-than-expected occurrences of myasthenia and autoimmune diseases within families.

Tumors

In myasthenia gravis with antibodies against “self” receptors, thymus abnormalities are common. About 15% of patients with myasthenia gravis develop a thymoma (a tumor of the thymus). Surgical removal of the thymus (thymectomy) can improve the condition. In approximately 50% of patients with LEMS, small cell lung carcinoma is present.

Treatment

Treatment for myasthenia involves:

• Medications to improve nerve-to-muscle signal transmission, such as pyridostigmine (Mestinon®)
• Immunosuppressive medications to reduce the autoimmune response, as most cases are caused by an immune reaction.

With proper treatment, significant improvement can be achieved. However, incorrect treatment can lead to life-threatening complications.

Precautions

Patients with myasthenia must exercise caution with medications prescribed for other conditions. Many drugs can worsen myasthenia symptoms, so careful consideration is required before prescribing.

Key Considerations:

• Thymus Evaluation: Regular checks for thymus abnormalities or thymomas in myasthenia gravis patients.
• Cancer Screening: High vigilance for small cell lung carcinoma in LEMS patients.
• Personalized Care: Treatment strategies must be tailored to individual forms and severities of the disease to prevent severe outcomes.