Myasthenia Gravis

What is Myasthenia Gravis?

Myasthenia gravis is a chronic neuromuscular junction (NMJ) disorder characterized by weakness of the skeletal muscles, which are the muscles the body uses for various movements. Myasthenia gravis is an autoimmune disease that occurs when the immune system attacks the body’s own tissues resulting in a decreased number of available acetylcholine receptors (AChRs) at NMJs. This antibody-mediated autoimmune attack is the underlying defect responsible for weakness in the skeletal muscles that worsens with activity and improves after periods of rest. These muscles are responsible for functions involving breathing and moving parts of the body, including the arms and legs.  The prevalence of Myasthenia gravis is 200 in 100,000 and It affects all age groups but affects women frequently than men. 

What are the different types of Myasthenia Gravis?

There are two forms of Myasthenia gravis and it includes:

  • Ocular Myasthenia Gravis: Eyelids and extraocular muscles are the only muscles affected
  • Generalized Myasthenia Gravis: the weakness affects ocular muscles, limb, and respiratory muscles.

What are the symptoms of Myasthenia Gravis?

Muscle weakness is the main symptom associated with myasthenia gravis and can include:   

  • Droopy eyelids
  • Blurry vision or double vision
  • Difficulty swallowing or chewing
  • Trouble talking 
  • Loss of expression on the face
  • Hoarse Voice
  • Difficulty breathing 
  • Generalized fatigue

How to diagnose Myasthenia Gravis?

Diagnosis of MG entails careful medical history and physical examination. The diagnosis is suspected based on the muscle weakness, without loss of reflexes or impairment of sensation or other neurologic function. Other tests that can be performed to evaluate MG includes:

  • Laboratory testing: It is a blood test performed to detect autoantibodies associated with MG and includes acetylcholine receptor (AChR) antibodies, anti-MuSK (muscle-specific kinase) antibodies, and anti-striated muscle antibodies

Non-laboratory tests include: 

  • Ice pack test: Application of ice pack over a droopy eyelid often results in improvement if it is due to an NMJ defect.
  • Tensilon test Edrophonium is given intravenously to see if muscle strength improves for a few minutes
  • Repetitive nerve stimulation: For evaluation of neuromuscular response in specific areas
  • Chest CT: To detect thymoma or enlarged thymus

How to treat Myasthenia Gravis?

  • Anticholinesterase medications:  include pyridostigmine or mestinon which slow the breakdown of acetylcholine at the neuromuscular junction and thereby improving muscle strength
  • Immunosuppressive drugs: include prednisone, azathioprine and other drugs which act by suppressing the production of abnormal antibodies
  • Plasmapheresis and intravenous immunoglobulin: plasma, which contains the abnormal antibodies are mechanically separated from the blood cells and are returned to the patient
  • Thymectomy:  This is the surgical removal of the thymus gland and can be a cure of the gland that is defective or may reduce symptoms possibly by rebalancing the immune system.

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