MYASTHENIA GRAVIS

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DEFINITION

Myastenia gravis is a disorder affecting the neuromuscular transmission of the voluntary muscles of the body.It is characterized by excessive weakness and fatiguability,particularly of the voluntary muscles and those innervated by the cranial nerves.

 

Myasthenia gravis is an autoimmune disorder affecting the myoneural junction,is characterized by varying degree of weakness of the voluntary muscles.

INCIDENCE
Women are affected more frequently than that of men,and they tends to develop disease at an younger stage.(20-40 years of age versus 60-70 years of age for men.
 
PATHOPHYSIOLOGY
Normally a chemical impulse precipitates the release of acetylcholine from the vescicles on the nerve terminal at the myoneural junction.The acetylcholine attaches to the receptor sites on the motor endplate and stimulates muscle contraction.Continuous binding of the acetylcholine to the receptor site is required for muscular contraction to be sustained
In Myasthenia gravis antibodies directed at the acetylcholine receptor sites impairs the transmission of the impulses across the myoneural junction.Therefore fewer receptors are available for stimulation,resulting in voluntary muscle weakness that escalates with continued activity.Eighty percent of the people with Myasthenia gravis has either thymic hyperplasia or a thymic tumor,and the thymus gland is believed to be the site of antibody production.
 
CLINICAL MANIFESTATIONS

• Occular disturbances.
• Diplopia and ptosis
• Weakness of the muscles of the face and the throat.(bulbar symptoms)and generalized weakness.Weakness of the facial muscles results in bland facial expression.
• Laryngeal irritation causes voice impairment and dysphonias and increases the patient s risk for choking and aspiration.
• Generalized weakness of all the extremities and the intercoastal muscles resulting in decreased respiratory capacity and vital capacity.
• Myasthenia gravis is purely a motor disorder with no effect on the sensation and coordination.

 
ASSESSMENT AND DIAGNOSTIC FINDINGS

• History collection and physical examination.
• Acetylcholinesterase inhibitor test-Actylcholinesterase inhibitor stops the breakdown of acetylcholine,thereby increasing the availability of neuromuscular junction.
• Endrophonium chloride(Tensilon)a fast acting acetyl cholinesterase inhibitor,is administered IV,to diagnose myasthenia gravis.Thirty seconds after the injection,muscle weakness and ptosis should resolve for about 5 minutes.Immediate improvement in the muscle strength after the administration of this agent indicates a positive test.Atropine should be available to control the sideeffects of endrophonium which includes bradycardia,sweating and cramping.

 
MEDICAL MANAGEMENT
Management of Myasthenia gravis includes improving function and reducing and removing circulating antibodies.Therapeutic modalties includes administration of anticholinesterase medications and immunosuppressive therapy,plasmapheresis and thymectomy.
 
SURGICAL MANAGEMENT

• Thymectomy can produce antigen specific immunosupression and can result in clinical improvement.The entire gland is removed for desired outcomes.,therefore the surgeon prefers transsternal surgical approach.
• After surgery the patient is monitored in an intensive care unit with special attension to the respiratory function.
• The patient is weaned from ventilator after health assessment.
• After the thymus gland is removed it may take about 3 years for the patient to benefit from the procedure because of the long life of circulating T cells

 
NURSING ASSESSMENT

• Assess the severity of the fatigue by asking the patient
• The patients coping ability nd understanding should be assessed.
• Objective data should include respiratory rate and depth,oxygen saturation,arterial blood gas analysis,pulmonary function tests,assessment of respiratory distress.Muscle strength of the face and the limbs should also be assessed.Assess for swallowing,speech,cough and gag reflexes

 
NURSING MANAGEMENT

• Patient and family teaching.Educational topics for outpatient self care includes medication management,energy conservation,strategies to help with ocular manifestations,prevention and management of complications.
• The patient is taught regarding the strategies to conserve the energy.To do this the nurse helps the patient to identify the optimal levels of energy an drest hours throughout the day.If the patient lives in a two storeyed home the nursecan suggest the frequently used items(hygiene products,cleansing products,snacks)be kept on each floor to minimize the travel between the floors.
• To minimize the risk of aspiration ,meal times should coincide with the peak effect of anticholinesterase medication the patient is advised to sit upright during the meals,with the neck slightly flexed to facilitate swallowing.Soft foods can be swallowed very easily.
• Supplimental feedings are needed if the nutritional status of the patient is not adequate.
• Impaired vision results from ptosis of one or both the eyelids,decreased eyemovement and double vision occurs.To prevent corneal damage when the eyelids doesnot close completely,the patient is instructed to tape the eyes closed for short intervals and to instill artificial tears.Pathes of one eye can help to prevent double vision..
• Identify the factors that precipitate the symptoms and eliminate those factors.
• Myasthenia crisis-Respiratory distress and varying degrees of dysphagia(difficulty swallowing),dysarthria(difficulty in speaking)eyelid ptosis,diplopia,and prominent muscle weakness are symptoms of myasthenia crisis.
• The patient is placed in an an intensive care unit for constant monitoring because of sudden fluctuations in the clinical conditions
• The nurse should assess the respiratory rate,depth and breath soundsand monitors pulmonary function parametersto detect pulmonary problems.
• Chest physical therapy,including postural drainage to mobilize secretions.
• Postural drainage shouldnot be performed for 30 minutes after the feeding.

Assessment strategies and supportive measures includes the following:

• ABG Values,serum electrolytes,input and output,an ddaily weight is monitored.
• If the patient cannot swallow nasogastric tube feeding is required.
• Sedatives and tranquillers are avoided,because they aggravates hypoxia and hypercapnea and can cause respiratory and cardiac depression.

 
NURSING DIAGNOSIS
Ineffective breathing pattern related to intercoastal muscle weakness

• Assess the respiratory rate ,depth and breathsounds and monitor the results of pulmonary function tests(tidal volume,vital capacity,inspiratory force)
• Encourage deep breathing and coughing exercise if the patient can tolerate
• Chest physiotherapy,postural drainage is given to immobilize the secretions
• Suctioning is done to promote the drainage of secretions
• Provide psychological support to the patient

 
Impaired physical mobility related to voluntary muscle weakness

• The patients goal is the improvement of the strength of the weakened muscles
• The patient should be educated about the basic facts about anticholinesterase agents-their action,timing,dosage,adjustmentsymptoms of overdose and toxic effects.The importance of taking the medication and the time should be emphasized.
• The patient is encouraged to keep a diary to note the fluctuation in symptoms.
• Time the meals to coincide with the peak effects of anticholinesterase medications
• Plan adequate rest periods throughout the day.
• Wear appropriate shoes to minimize injury.
• Eliminate the factors which will cause elevation of the symptoms(emotional upset,infections,particularly respiratory infections,vigorous physical activity etc..
• Encourage to use cervical collar if there is neck weakness

 
Risk for aspiration related to weakness of the bulbar muscles

• The patient should be assessed for drooling,regurgitation through the nose,choking while attempting to swallow etc...
• Rest before the meals is encouraged to reduce muscle fatigue
• The patient is seated in an upright positionwith the neck slightly flexed to facilitate swallowing
• Soft food is encouraged
• Since the muscles of swallowing will be stronger in the morning,caloric intake can be increased for breakfast.The patient is encouraged to rest after breakfast
• Suction should be available at the home if there is risk of aspiration

 
Impaired verbal communication related to weakness of the larynx ,lips,mouth,paharynx and jaw

• The weakened muscles will interfere with verbal communication
• Techniques for improving the communication includes listening to the patients,repeating what they are trying to communicate and asking the patient to blink their eyes for yes or no answers

 
Disturbed sensory perception related to ptosis,and decreased eye movements.

• Impaired vision results from ptosis,decreased eye movements or double vision
• Measures includes instilling artificial tears into the eyes to prevent corneal damage when the eyelids willnot close completely
• Placing eye patch when there is double vision.
• Applying a thin adhesive tape over the eyelid if there is ptosis.
• Sunglasses reduces the effect of bright light

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