Myasthenia Gravis : Symptoms, Diagnosis, Treatment

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In this blog, we will learn about Myasthenia gravis disease.

myasthenia gravis

Myasthenia gravis is an autoimmune disease of neuromuscular junction caused by antibodies to cholinergic receptor. It is characterized by progressive fatigable weakness, particularly of the ocular, neck, facial and bulb are muscles.

This problem occurs due to inability of neuromuscular junction to transmit impulses from nerve to the muscle

First we have to understand how neuromuscular junction works and how it transmit the impulse. So, we can understand this disease completely. 

When action potential reaches to the axon terminal, chemical named acetylcholine (Ach) release from synaptic vessicle in neuron.

action potential —> Ach release

Than acetylcholine comes in synaptic cleft and make complex with receptor. It is called acetylcholine receptor complex. This is important part to under myasthenia gravis disease condition.

Ach receptor complex —> potential in muscle

After making complex, Na+ enters in muscle. When Na+ enters, it means positivity occurs in muscle. So, muscle contract after this process.

It means that when you do any activity of muscle, this whole process need to happen. If there is any problem in between than muscle can not work properly.

Same thing happen in myasthenia gravis disease. It is neuromuscular junction disorder. In which antibodies develop against acetylcholine receptor. So, acetylcholine receptor complex can not form. Altimately proper message can not convey from neuron to muscle & patient is suffering from muscle weakness and tiredness.

antibodies to receptor

Pathophysiology

This disease is most commonly caused by antibodies to acetylcholine receptors in the post-junctional membrane of the neuromuscular junction.

This antibodies block neuromuscular transmission. It prevent binding of acetylcholine with it receptor or destroy the receptors. So, though the acetylcholine release is normal, it cannot execute its action.

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Symptoms of Myasthenia Gravis

As I earlier describe that in this disease message releases from brain can not reach properly to muscle. So, symptoms of myasthenia patient are mostly of muscle weakness and tiredness. Worsening of the symptoms toward end of the day or following exercise is characteristic.

  1. Eye
    First symptoms usually belongs to eye. Due to muscles weakness patient suffer from drooping of the eyelids called ptosis or may suffer from double vision called diploma
  2. Face
    Difficulty in speech due to weakness of muscles of speechDifficulty in swallowing due to weakness of throat musclesPatient can not give snarling smile and due to jaw muscle weakness patient have difficulty in chewing
  3. Neck
    Weakness of neck muscles may cause head drooping
  4. Extremities
    Slow and weak muscular contraction because of the defective neuromuscular activity. The cardinal symptom is fatigable weakness of the muscles. Movement is initially strong but rapidly weakens as muscle use continues. Inability to maintain the prolonged contraction of skeletal muscle. Patient can not combing the hair without frequent rests.Quick fatigability when the patient attempts repeated muscular contraction. If we tell patient to raise hand for 20 times, he can not do so. Immediately he suffer from weakness from that part.
  5. Respiratory
    Respiratory muscle involvement can be life threatening. Shortness of breath, particularly on lying flat is common. Reduced arterial oxygen capacity is a late sign of respiratory failure. In severe conditions, there is paralysis of muscles. Patient dies mostly due to the paralysis of respiratory muscles.

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Investigation of Myasthenia Gravis

  1. Anti-AChR antibodies
    This antibodies are detectable in the blood in most of the patients.
  2. Tensilon test
    The intravenous injection of the short-acting anticholinesterase, endophonium bromide, is a valuable diagnostic aid. 2mg is injected initially, with a further 8mg given half a minute later if there is no undesirable side-effects. Improvement in muscle power occurs within 30 seconds and usually persist for 2-3 minutes. By this way we can diagnose.
  3. EMG test
    It shows decreasing muscle action potential with rapid stimulation.

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Management

The principles of treatment are

  • to maximize the activity of acetylcholine at remaining receptors in the neuromuscular junctions
  • to limit or abolish the immunological attack on motor end plates.

Drug therapy 

Anticholinesterase

The main function of cholinesterase is to destroy Ach. If we give anticholinesterase like pyridostigmine or neostigmine, the amount of Ach will remains high. This will help in improvement of symptoms in myasthenia gravis.

Immunotherapy

Prednisolone alone or with azathioprine as a cortical sparing agent, is the first line immunotherapy. 

Thymectomy

Should be considered in any antibody positive patient under 45 years with symptoms not confined to extra-curricular muscles, unless the disease has been established for more than 7 years.

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