Myasthenia gravis - causes, symptoms, treatment, pathology

Summary

Myasthenia gravis is an autoimmune disorder characterized by muscle weakness, particularly affecting the skeletal muscles. It leads to symptoms like progressive weakness throughout the day, double vision, and drooping eyelids. The condition predominantly impacts young women and older men, with an unclear cause for this age distribution. The disease is a type II hypersensitivity, where autoantibodies target acetylcholine receptors on muscle cells, hindering muscle contraction signals. Treatment includes acetylcholinesterase inhibitors to increase acetylcholine levels, immunosuppressive drugs to reduce antibody production, and thymus removal. This informative script sheds light on the mechanisms and management of myasthenia gravis.

Takeaways

• 💊 Myasthenia gravis is an autoimmune disease that causes muscle weakness, particularly affecting skeletal muscles.
• 🌞 Patients might experience fluctuating strength levels throughout the day, with symptoms worsening as the day progresses.
• 👁️ Myasthenia gravis can impact the extraocular muscles, leading to double vision (diplopia) and drooping eyelids (ptosis).
• 👧👴 The disease has a bimodal age distribution, predominantly affecting young women in their 20s and 30s and older men in their 60s and 70s.
• 🔬 In a normal muscle contraction, motor neurons release acetylcholine, which binds to receptors on muscle cells, triggering a chain reaction for muscle movement.
• 🛡️ Myasthenia gravis is a type II hypersensitivity disorder where autoantibodies target and damage host cells, specifically the nicotinic acetylcholine receptors on muscle cells.
• 🚫 Antibodies in myasthenia gravis prevent acetylcholine from binding to its receptors, blocking the muscle contraction signal from the nervous system.
• 🔄 The complement system, activated by the antibodies, causes inflammation and destruction of muscle cells, further reducing acetylcholine receptor availability.
• 🏥 Some patients produce muscle-specific receptor tyrosine kinase antibodies, which attack internal muscle cell proteins, leading to cell destruction.
• ⚠️ In rare cases, myasthenia gravis can be a paraneoplastic syndrome, associated with underlying cancers that trigger autoantibody production.
• 💊 Treatment options for myasthenia gravis include acetylcholinesterase inhibitors, immunosuppressive drugs, and surgical thymus removal to alleviate symptoms.

Q & A

What is the literal meaning of 'Myasthenia gravis'?

Myasthenia gravis is a Latin expression that literally means 'grave muscle weakness', which describes the severe muscle weakness associated with this condition.

How does myasthenia gravis affect the skeletal muscles?

Myasthenia gravis is an autoimmune disease that affects the skeletal muscles, causing them to become progressively weaker throughout the day, especially with repetitive movements.

What are the symptoms related to the extraocular muscles in myasthenia gravis?

Myasthenia gravis can affect the extraocular muscles, leading to symptoms such as diplopia (double vision) and ptosis (drooping eyelids).

Which age groups are predominantly affected by myasthenia gravis?

Myasthenia gravis preferentially affects young women in their 20s and 30s, and older men in their 60s and 70s.

What is the normal process of muscle contraction at the cellular level?

Normal muscle contraction involves motor neurons releasing acetylcholine at the neuromuscular junction, which binds to nicotinic acetylcholine receptors on muscle cell membranes, triggering a chain reaction that results in muscle contraction.

How does myasthenia gravis interfere with the normal muscle contraction process?

In myasthenia gravis, the patient's B cells produce antibodies that bind to and block the nicotinic acetylcholine receptors, preventing the muscle cells from responding to the 'contract' signal from the central nervous system.

What is the role of the complement system in myasthenia gravis?

The complement system, a family of small proteins that fight off bacterial infections, is activated by anti-acetylcholine receptor antibodies in myasthenia gravis, causing inflammation and destruction of muscle cells and reducing the number of acetylcholine receptors.

What are muscle specific receptor tyrosine kinase antibodies, and how do they affect myasthenia gravis?

Muscle specific receptor tyrosine kinase antibodies are another type of harmful antibody found in a minority of people with myasthenia gravis. They attack proteins inside muscle cells, leading to the destruction of healthy cells.

Can myasthenia gravis be related to an underlying cancer?

In very rare cases, myasthenia gravis can present as a paraneoplastic syndrome, where an underlying cancer generates an immune response that results in the production of autoantibodies.

What is a myasthenic crisis, and how can it be life-threatening?

A myasthenic crisis is a life-threatening manifestation of myasthenia gravis where certain muscles, such as those controlling breathing, experience decreased function, potentially leading to respiratory failure.

What are some treatments for myasthenia gravis?

Treatments for myasthenia gravis include acetylcholinesterase inhibitors like neostigmine or pyridostigmine to increase acetylcholine concentration, immunosuppressive drugs like prednisone to reduce harmful antibody production, and surgical removal of the thymus.

Why is the removal of the thymus beneficial in treating myasthenia gravis?

The removal of the thymus, even in the absence of identifiable thymus gland problems, can reduce muscle weakness symptoms in myasthenia gravis, possibly because helper T cells that originate in the thymus aid B cells in making antibodies to the acetylcholine receptor.