Myasthenia gravis is characterized by weakness and rapid fatigue of any of skeletal muscles.
The most commonly affected muscles are these of the eyes, face & swallowing. It results in double vision, drooping eyelids, trouble in talking and walking.
M.G is an autoimmune disease which results from antibodies that destroy nicotinic acetylcholine receptors at the junction between the nerve and muscle, hence prevents nerve impulses from triggering muscle contraction.
Muscle weakness caused by MG worsens as the affected muscle is used repeatedly. Although MG can affect any of the skeletal muscles, certain muscle groups are more commonly affected than others.
The initial symptom of MG is related to the weakness to the muscles around the eye.
There may be ptosis (eyelid drooping) due to the weakness of levator palpebrae superioris and diplopia (double vision) due to the weakness of the extraocular muscles. Eye symptoms tend to get worse when being in a bright condition, watching television or driving.
The weakness in muscles involved with eating lead to dysphagia (swallowing difficulty) weakness of muscles of mastication (muscles that move jaw) may cause difficulty chewing.
Speech may become slow and slurred or have a nasal quality. This leads to dysarthria and hypophonia.
HEAD AND NECK
Due to the weakness of muscles of faces, facial expression may manifest as the inability to hold the mouth and give a growl expression when attempting to smile. Difficulty in holding the head up straight may occur too.
Myasthenia Gravis is an autoimmune synaptopathy. This disorder occurs when the immune system malfunctions and generates antibodies that attack the own body cells. These antibodies basically attack a normal human protein, the nicotinic acetylcholine receptor or a protein called MuSK (Muscle-specific kinase).
In patients with M.G, the thymus gland is large and perform abnormal functions, thus gives wrong instructions to immune cells.
Doctors may check your neurological health by testing your: –
· Muscle strength
· Muscle tone
· The sense of touch and Sight
Injection of the edrophonium chloride(Tensilon) may result in sudden temporary improvement in muscle strength. This increase in muscle strength is an indication that you have Myasthenia Gravis.
Edrophonium chloride blocks an enzyme that breaks down acetylcholine.
Ice Pack test
In this test, a bag filled with ice is placed on your eyelid. The basis of this test is that Acetylcholinesterase is thought to be initiated at low temperature. This test is considered positive if more than or equal to 2mm rise in eyelid occurs after the ice is removed.
ELECTROMYOGRAPHY OR ELECTRODIAGNOSTICS
EMG measures the electrical activity traveling between your brain and muscles. It involves inserting a fine wire electrode through your skin & into a muscle to test a single muscle fiber.
A chest X-ray may identify widening of the mediastinum suggestive of THYMOMA, but MRI & CT scans are more sensitive ways.
PULMONARY FUNCTION TEST
This test is performed to check whether your condition is affecting your breathing or not.
A blood test may reveal the presence of abnormal antibodies that disrupt the receptor sites where nerve impulses signal your muscles to move.
· Cholinesterase Inhibitor- Medicines such as Pyridostigmine, enhances communication between nerve and muscles. These medications don’t cure the disease but improve muscle contraction & strength
Side effects may include- 1) Gastrointestinal abnormality
3) Excessive salivation and sweating
Corticosteroids such as prednisone inhibit the antibody production
Side effects-1) Bone thinning
2) Weight Gain
4) Increased risk of infection
These medications alter the immune system such as AZATHIOPRINE, MYCOPHENOLATE MOFETIL, CYCLOSPORINE, METHOTREXATE or TACROLIMUS (Pangraff)
Side effects include- 1) Nausea
4) Liver damage
· PLASMAPHERESIS- This procedure is similar to dialysis in which your blood is routed through a machine which removes the antibodies which block the neuron transmission.
Side effects- 1) Drop in B.P
3) Heart rhythm problems
4) Allergic reactions
· INTRAVENOUS IMMUNOGLOBULIN(IVIg)
In this therapy abnormal antibodies of your body are replaced with normal antibodies.
IVIgs has a lower risk of side effects than plasmapheresis.
Side effects- 1) Mild chills
4) Fluid retention
· Monoclonal Antibody- In this therapy an intravenous immunosuppressive medication called RITUXIMAB (MABTAS RA) is used. This dug depletes certain WBCs, altering the immune system and improving MG.
Side effects- 1) Febrile neutropenia
6) Decreased WBSs
7) Increased risk of infection
A thymectomy is an operation to remove the thymus. It usually results in remission of M.G with the help of medication including steroids. The doctor will only conduct thymectomy if you have THYMOMA.
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