Myasthenia Gravis:

  • Chronic autoimmune neuromuscular disease define as weakness in skeletal muscles after periods of activities & usually caused by an acquired immunological abnormality.

Pathophysiology:

Clinical manifestations:

  • Complained of no pain, no fatigue but with specific muscle weakness.

Ocular myasthenia:

  • The weakness is limited to the eyelids and extraocular muscles (e.g: droopy eyelids or double vision is the most common symptom at initial presentation of Myasthenia Gravis affecting more than 75% of patients).
    General disease:
  • The weakness commonly affects ocular muscles, but it also involves a variable combination of bulbar, limb, and respiratory muscles


  • Can impair speaking in which your speech might sound soft or nasal, depending on which muscles have been affected and muscles get weaker with repeated use in the end.

Complications:

  • It affects the voluntary muscles of the body, especially those that control the eyes, mouth, throat & limbs.
  • Fatigue, illness, stress, extreme heat & medications, such as beta blockers, quinidine gluconate, quinidine sulfate, quinine, phenytoin, some anesthetics or some antibiotics could worsen the condition & lead to Myasthenia Crisis in which it affects breathing & swallowing.
  • Thymus tumors.
  • More likely to have underactive or overactive thyroid & other autoimmune conditions, such as rheumatoid arthritis & lupus.

Contributing factors:

Thymus gland (TG):

  • Control immunity
  • Growing gradually until puberty.
  • When one reach puberty, TG is smaller in size and replaced by fat .
  • Pt with MG, their TG remain large.
  • 10% of pt hv a thymoma (tumor in TG) & 70% hv hyperplasia changes (germinal centers) that indicate an active immune response and incorrect instructions which can cause immune system to attack own cells or tissues and produce AChR Autoantibodies by interaction B-cells with the Helper T-cells.

How muscle can contracts & cannot contracts:

  • For normal neuromuscular transmission, impulses/electrical signals send to motor nerve known as motor end-plate. Synaptic vesicles filled with chemical impulses- Acetylcholine (ACh) then fuse with presynaptic membrane which release into synaptic cleft. Reversible binding of ACh to the nicotinic ACh receptors (AChR) at the muscle membrane which open the receptor of ion channel and influx of the ions. Then, activates the muscles to contract which depolarization the action potential. Breakdown of ACh by cholinesterase and re-uptake to motor end-plate.
  • For abnormal or impaired neuromuscular transmission, Antibodies compete with ACh for postsynaptic AChRs which can lead to ACh cannot bind to AChR so receptor of ions channel also does not open and no neuromuscular transmission. To be clear, no muscle contraction and no depolarization of action potential.

Gender:

  • Female > male
  • Possible at any age but most common/higher risk are young female & older male.
  • Young female: 20-40 yrs old.
  • Older male: 60-80 yrs old

Family history:

  • Autoimmune diseases

Assessment

Diagnostic tests:

  1. Muscle strength
  • Limb weakness:
    (Instruct patient to lift arms to 90 degrees. Check for shoulder’s abduction and adduction; IF equal, ask them to move up and down one of their arms for 20 times to fatigue the muscles. Then, retest shoulder abduction and adduction. For Myasthenia Gravis’ patient, both abduction and adduction demonstrated with weaker than unused arm.)
  • Ocular myasthenia:
    (Sustained upgaze and repeated blinking. Repeating eye movement testing after sustaining the upgaze or repeated blinking; will exacerbate any weakness and bring out diplopia and ptosis from use the relevant muscles.
  1. Muscle tone
  2. Sense of touch & sight
  3. Coordination & balance
  4. Reflexes

Laboratory tests:

  1. Blood test
  • To measure the presence of acetylcholine receptor antibodies. Most of these patients show an elevation amounts of antibodies in blood. If no elevation of acetylcholine receptor antibodies, MuSK antibody is increase.

Other tests:

  1. CT scan
  • CT Scan / MRI scan to check the enlargement of thymus gland.
  1. Nerve test (Electromyogram)
  • To assess nerve and muscle function electrically- shows whether the signals sent from the nerves to the muscles are being disrupted; sign of myasthenia gravis.
  1. Edrophonium test/Tensilon test
  • Edrophonium chloride injected to patient, if patient experience sudden but temporary improvement in muscle strength; shows it is myasthenia gravis.

Pharmacotherapeutics

  1. Anticholinesterase inhibitor
  • Works at neuromuscular junction to prevent the breakdown of acetylcholine.
    -Allows acetylcholine to bind to more muscle receptors and create muscle contractions.
  • Common drugs: Pyridostigmine bromide & Neostigmine bromide.
  • Pyridostigmine is preferred drug because it has smoother dose response curve & longer duration of action than neostigmine and fewer gastric effects; the effect of neostigmine tends to drop rapidly after it peaks and this can complicate the timing of doses.
  • Pyridostigmine does not alter myasthenia gravis disease, but provides temporary symptom improvement.
    -Anticholinesterase are contraindicated in patients with asthma, cardiac conduction defects, urinary and intestinal obstruction.
  1. Immunosuppression
  • Work to lower the immune system response in order to prevent the immune attack on the NMJ, thereby limiting muscle fatigue.
  • Prednisolone, Azathioprine,Methotrexate/ Mycophenolate Mofetil.
  • While on med: Limit exposure to colds & flus, vaccinations should be up to date, including the flu and pneumonia vaccines.
  1. Intravenous immune globulin
  • Given through a small, peripheral catheter.
  • Binds to the antibodies in bloodstream and then is filtered out of the body by the kidneys.
  • Consists of immune globulins collected from donors & acts to destroy and neutralize these autoantibodies in the bloodstream and block the production of new antibodies.
  • During the infusion heart rate and blood pressure are monitored, it is used for emergency situations when you have difficulty breathing or swallowing.
  1. Plasmapheresis (plasma exchange)
  • Remove the Ach receptor antibodies from the blood, is sometimes used to give symptom relief.
  • Used in a myasthenic crisis along with intravenous corticosteroids.
  • Treatment that requires insertion of a large catheter, blood is then filtered through a machine to pull out proteins, which contain the antibodies.
  • During the filtering process, heart rate and blood pressure are monitored.
  • Used for emergency situations when you have difficulty breathing or swallowing.

Surgical interventions:

1. Thymectomy

  • The relationship between the thymus gland and myasthenia gravis has led to the medical recommendation that the gland be removed (thymectomy).
  • Full Sternotomy: An incision is made down the middle of the chest through the sternum in order to expose the thymus gland.
  • Partial Sternotomy: A smaller incision is made down the middle of the chest through only half of the sternum is separated in order to expose the thymus gland.
  • Thoracoscopic Thymectomy: With the thoracoscopic technique, the surgeon makes 2 to 3 small incisions (3/4 inch in length) on the side of the chest.
  • Transcervical Thymectomy: A small horizontal incision is made across the lower part of the neck.
  1. Strabismus surgery
  2. Ptosis surgery

Prioritize Nsg Care

Nsg diagnosis: Ineffective breathing pattern related to fatigue & respiratory distress as evidenced by respiration rate of 26.

Nsg intervention:

  1. Monitor respiratory rate of the pt to see if there is any possibility of respiratory distress/cholinergic crisis.
  2. Place pt in semi-Fowler position. This position helps to expand lungs & alleviate pressure from the diaphragm.
  3. Encourage deep breathing & coughing exercise to the pt. This exercise helps to lower the stress to the body.
  4. Maintain patent airway so that can receive adequate oxygenation.
  5. Administer medication as prescribed such as Pyridostigmine to treat the symptoms of MG.

Nsg diagnosis: Impaired swallowing related to mild dysphagia.

Nsg intervention:

  1. Assess pt's swallowing & gag reflex. This is because lungs usually protected against aspiration by reflexes gags/cough. When there is deppression, pt will be in high risk for aspiration.
  2. Observe signs associated with swallowing problems such as coughing, choking, spitting of food & etc.
  3. Check for food & fluid regurgitation that indicates decreased ability to swallow foods/fluids & increased in aspiration.
  4. Evaluate the results of swallowing studies as ordered like video fluoroscopic swallow study. This is to determine swallowing abnormality.