Myasthenia Gravis – Causes and Risk Factors, Pathophysiology, Clinical Manifestations and Management

Myasthenia Gravis – Causes and Risk Factors, Pathophysiology, Clinical Manifestations and Management

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Myasthenia Gravis – Causes and Risk Factors, Pathophysiology, Clinical Manifestations and Management

Myasthenia gravis (MG) means “grave muscle weakness” or weakness of the voluntary or striated muscles of the body. Myasthenia gravis is a chronic autoimmune disorder affecting the neuromuscular transmission of impulses in the voluntary muscles of the body. It is characterized by weakness and rapid fatigue of any of the muscles under voluntary control. Neuromuscular disorders involve the muscles and the nerves that control them.

CAUSES AND RISK FACTORS

Myasthenia gravis is caused by a defect in the transmission of nerve impulses to muscles. It occurs when normal communication between the nerve and muscle is interrupted at the neuromuscular junction-the place where nerve cells connect with the muscles they control.

  • The cause of autoimmune disorders such as myasthenia gravis is unknown
  • Tumors of the thymus (an organ of the immune system)
  • Thyroid gland abnormalities
  • Autoimmune attacks: thyrotoxicosis, rheumatoid arthritis and systemic lupus erythematosus
  • Myasthenic Crisis: may result from natural deterioration, emotional upset, upper RTI, surgery, trauma or ACTH therapy.
  • Cholinergic Crisis: can result from overmedication with anticholinergic drugs which release too much acetylcholine at the neuromuscular junction


 

PATHOPHYSIOLOGY

The body’s immune system is activated -------- Thymic lymphocytes produce acetylcholine – receptor antibodies that attack the postsynaptic muscle membrane at the neuromuscular junction -------------- Depletion of acetylcholine receptors at the neuromuscular junction ---------- Fewer receptors are available to combine with acetylcholine to trigger a muscle action potential; prevents the muscle contraction ----------- Defect in the transmission of impulses from nerve to muscle cells -------- Loss of voluntary muscle strength --------- Myasthenia Gravis

 

CLINICAL MANIFESTATIONS

The muscle weakness of myasthenia gravis worsens with activity and improves with rest. Weakness in affected muscles may cause:

  • Breathing difficulty because of weakness of the chest wall muscles
  • Chewing or swallowing difficulty, causing frequent gagging, choking, or drooling
  • Difficulty climbing stairs, lifting objects, or rising from a seated position
  • Difficulty talking (slurred speech)
  • Impaired speech (dysarthria)
  • Drooping head
  • Facial paralysis or weakness of the facial muscles
  • Mask – like facial expression
  • Easy fatigability
  • Hoarseness or changing voice
  • Difficulty maintaining steady gaze and eyelid drooping
  • Drooping of one or both eyelids (ptosis)
  • Blurred or double vision (diplopia)
  • Shortness of breath
  • Weakness is the arms, hands, fingers, legs and neck


 

DIAGNOSTIC EVALUATIONS

  • Medical history and physical and neurological examinations
  • Test to detect actetylcholine receptor antibodies
  • CT or MRI scans of the chest
  • Repetitive nerve stimulation
  • Single-fiber electromyography (EMG)
  • Pulmonary function testing
  • Edrophonium test: Injection of the chemical edrophonium (Tensilon) is injected IV, 2 mg at a time to a total of 10 mg. 30 seconds after injection, may result in a sudden, although temporary, improvement in muscle strength. Edrophonium acts to block an enzyme that breaks down acetylcholine, the chemical that transmits signals from nerve endings to muscle receptor sites.


There is no known cure for myasthenia gravis. However, treatment may result in prolonged periods without any symptoms (remission). Many people with the condition become completely free of symptoms with treatment, and most can lead a normal or nearly normal life.

Cholinesterase Inhibitors: Medicines known as cholinesterase inhibitors such as pyridostigmine and neostigmine can block the action of the chemical that normally makes the muscles relax once they have contracted and provide symptomatic relief. These medicines can improve muscle contractions and muscle strength in the affected muscles.
Medication to alter the immune system: Steroids (prednisolone) or immunosuppressant drugs (azathioprine) can damp down the body’s immune system and reduce the production of the antibodies that cause myasthenia gravis.
Plasmapheresis and immunoglobulin therapy: If myasthenia gravis muscle weakness becomes so severe that it causes life- threatening breathing or swallowing problems, plasmapheresis or intravenous immunoglobulin therapy can be given.
Thymectomy: Surgical removal of the thymus reduces symptoms in some individuals without thymoma and may cure some people, possibly by re-balancing the immune system. Thymectomy is recommended for individuals with thymoma.

 

NURSING MANAGEMENT

Nursing Diagnosis

  • Ineffective Breathing Pattern related to respiratory muscle weakness.

  • Impaired Physical Mobility related to weakness of voluntary muscles.

  • Risk for Aspiration related to the weakness of bulbar muscles.

  • Imbalanced Nutrition: Less than Body Requirements related to dysphagia, intubation, or muscle paralysis.

  • Self-Care Deficit related to muscle weakness, general fatigue.


 

Nursing Interventions

  • The primary nursing concerns focus on the adequacy of the patient’s airway and breathing. Keep suction equipment and intubation supplies at the patient’s bedside.
  • For meals, place the patient in a completely upright position. Instruct the patient to swallow only when the chin is tipped downward and never to speak with food in his or her mouth.
  • To prevent pulmonary complications, encourage the patient to perform deep breathing and coughing to enhance ventilation.
  • If the patient requires surgery, instruct him or her on chest splinting during deep breathing and coughing exercises. Keep the patient’s pain under control before all breathing exercises.
  • Ensure adequate nutritional intake and observe for signs and symptoms of dehydration or malnutrition.
  • Work with the patient and family to plan for foods that are easy to chew and swallow but are still appealing to the patient.
  • Assist the patient in developing a method for reliable communication. Fear of sudden respiratory distress and the inability to call for help or to reach a call light is very real.
  • Advise patient to prevent muscle fatigue with frequent rest periods. Instruct patient to participate in walking exercises to improve gait affected by loss of position sense in legs.