Myasthenia Gravis “MG”

Question 1

Myasthenia Gravis “MG”

Answer 1

Neuromuscular disease characterized by fluctuating weakness and fatigability of skeletal muscles
The incidence of MG is 1:200,000
Can affect people in any age group, but peak incidences occur in women in their twenties and thirties and men in their fifties and sixties
The ratio of women affected compared to men is 3:2
Life expectancy is unaffected

Question 2

Is an autoimmune disorder affecting the

Answer 2

neuromuscular junction and motor endplate
Receptors at the motor endplate normally receive Ach from the motor nerve terminal causing an action potential leading to muscle contraction
In MG, the number of receptors are decreased or their shape is distorted causing a decreased efficiency at this junction
The neuromuscular abnormalities are brought about by an immune response mediated by specific anti-Ach receptor antibodies
The antibodies may block or damage the postsynaptic muscle membrane
The cause of the autoimmune response is not well understood but the thymus appears to play a role
75% of people have abnormalities of the thymus (thymic hyperplasia or thymoma)

Question 3

Risk Factors

Answer 3

Some disorders associated with an increased incidence of MG are:
Thymic disorders: hyperthyroidism, thymic tumor, thymotoxicosis
Diabetes
Immune disorders – lupus, rheumatoid arthritis
Exacerbations may occur before the menstrual period or shortly after pregnancy; chronic infections may also exacerbate MG
5% to 7% have a familial association
Can be mild to severe
Cardinal features are skeletal muscle weakness and fatigability
Other than weakness, neurologic findings are normal
Repetition of activity causes fatigue whereas rest restores activity
Distribution of muscle weakness follows two patterns:
Affecting only ocular muscles
Muscles controlling eyelid and eye movements are first to show weakness
Diplopia and ptosis are common early signs
85% of people with MG have weakness that is generalized and affects the limb musculature; more noticeable in proximal muscles
Chewing of meat is fatiguing and facial expression looks like a snarl due to the inability to close the lips
Speech tends to be nasal
Swallowing may be affected as a result of palatal, pharyngeal and tongue weakness
Nasal regurgitation and aspiration of food is common
Respiratory impairment is a serious complication of MG

Question 4

History and clinical observation of symptoms

Answer 4

weakness with continued use and improvement with rest are important in diagnosing MG.
Several conditions that cause weakness of cranial, or somatic, muscles must also be considered
The three methods used to diagnose MG are:
Immunologic
Pharmocologic
Electrophysiologic

Question 5

Prognosis

Answer 5

Follows a slow progressive course
Typified by exacerbations and remissions
Symptoms fluctuate in intensity during the day
The onset of other systemic disorders and infections may exacerbate the disease which is the most common cause of a crisis
Myasthenic crisis – is a medical emergency requiring attention to life-endangering weakening of the respiratory muscles
Requires ventilatory assistance
Treatment occurs in the ICU

Question 6

Special Considerations

Answer 6

Deep breathing and coughing should be encouraged.
The person with MG should avoid strenuous exercise, stress and excessive exposure to sun or cold weather
Frequent rest periods help conserve energy and give muscles a chance to regain strength
Plan activities to coincide with periods of maximum energy
Researchers have reported that a strength training program of maximal isometric contractions could be instituted in clients with mild to moderate MG
Individuals diagnosed with MG are placed on long-term corticosteroid medications which may induce osteoporosis
Avoid joint play and aggressive mobilization techniques such as rib springing