MYASTHENIA GRAVIS
It is a disorder affecting the neuromuscular transmission of the voluntary muscles of the body; it is characterized by excessive weakness and fatigability particularly of voluntary muscles and those innervated by cranial nerve function.
Incidence: Affects younger women and men later in life.
Pathophysiology
It is a defect in the transmission of impulses from nerve to muscle cells (due to loss of available or normal receptors on the post synaptic membrane of the neuromuscular junction). It is considered an autoimmune disease (in which Abs directed acetylcholine receptor (AchR (impair neuromuscular transmission)
Clinical Manifestations
Extreme muscular weakness, easy fatigability (which generally is worse after effort and is relieved by rest). Patients tire on slight exertion. (as combing the hair, chewing and talking and must stop for rest).
Diplopia (double vision) and ptosis (drooping of the eyelids) sleepy masklike. expression (because the facial muscles are affected).
Dysphonia (Voice impairment) (laryngeal involvement) (Weakness of the bulbar muscles causes) problems with chewing and swallowing and (presents) a danger of choking and aspiration.
Weakness of arm and hand muscles and less commonly, of leg muscles which subject these patients to falls. Progressive weakness of the diaphragm and intercostals muscles respiratory distress or myasthenic crisis (acute emergency).
Diagnostic evaluation
Patient's history, physical examination. An injection of Edrophonium (Tensilon), (a drug that facilitates the transmission of impulses at the myoneural junction. Within 30 seconds of an IV injection, most patients improve substantially but only temporarily represents a positive test and usually confirms diagnosis of myasthenia.
Demonstration of the anti acetylcholine receptor (AchR) antibodies in the serum is found in nearly 90% of patients with generalized myasthenia and in 70% of those with symptoms restricted to the eye muscles.
Electromyography (EMG) - measures the electrical potential of muscle cells.
Medical Management
1. Anticholinesterase drugs act by increasing the relative concentration of available acetylcholine at the neuromuscular junction. The increase the response of the muscles to nerve impulses and to improve strength. They only provide symptomatic relief.
Eg. Pyridostigmine bromide (Mestinon), ambenonium chloride (Mytelase) and neostigmine bromide (Prostigmin) (Nursing priority - give drug prescribed according to exact time schedule to control the patients symptoms. Any delay in drug administration may result in the patients inability to swallow. An increase in muscle strength within 1 hr. after the administration of the anticholinesterase drug is expected).
2. Immunosuppressive therapy
- Corticosteroids suppress the patient's immune response thus decreasing the amount of blocking antibody. (The anticholinesterase dosage is lowered while the patient's ability to maintain effective respiration and to swallow is monitored).
- Plasma exchange permits selective removal of the patient's plasma and plasma components. The remaining cells are reinfused produces a temporary reduction in the titre of circulating Abs.
- Thymectomy-surgical removal of the thymus (Thymus involved in the process of AchR antibody production).
- Thymectomy is carried out through the sternum because the entire thymus must be removed.
Nursing Management
1. Plan exercise, meals and other ADLs during energy peaks. Time administration of medications 30 minutes before meals to facilitate chewing and swallowing.
2. Assist the patient in developing realistic activity schedule.
3. Provide an eyepatch and alternate eyes for the patient with diplopia to allow safe participation in activity.
4. Allow for rest periods throughout the day.
5. Obtain assistive devices to es to help patient perform ADLs.
6. Assess patients oral motor strength before each meal.
7. Teach patient to position head in a slightly flexed position to protect airway during eating.
8. Modify diet as needed to minimize risk of aspiration; for instance, soft, solid foods instead of liquid. instruct to chew food thoroughly and eat slowly. Stress importance of adequate nutrition.
9. Administer IV fluids and nasogastric tube feedings to patient in crisis or with impaired swallowing; elevate head of bed after feeding.
10. Suction the patient frequently if on a mechanical ventilator; assess breath sounds and check chest x-ray reports, because aspiration is a common problem.
11. Encourage patient to use an alternate communication method, such as flash cards or a letter board, if speech is affected.
12. Instruct patient to speak in a slow manner to avoid voice strain; refer to speech therapy as needed.
13. Show the patient how to cup chin in hands during speech to support lower jaw and assist with speech.
14. Teach patient to tilt head and to carry a handkerchief to manage secretions in public.
15. Encourage family participation in care.
16. Assess home environment for physical and emotional stressors, such as comfortable temperature, draft, loud noises and encourage avoidance of such.
17. Emphasize continued follow-up and compliance with treatment regimen.
18. Review the peak times of medications and how to schedule activity for best results. For patients on anticholinesterase therapy.
a. Stress accurate dosage and times.
b. Tell patient not to skip medication.
c. Instruct patient to avoid taking medication with fruit, coffee, tomato juice or other medications.
d. Inform patient of adverse side effects such as Gl distress.
19. Stress the importance of schedules rest periods before fatigue develops.
20. Teach patient ways to prevent crisis and aggravation of symptoms.
a. Avoid exposure to colds and other infections.
b. Avoid excessive heat and cold and emotional stress.
c. Inform the dentist of condition, because use of procaine is not well tolerated.
21. Encourage patient to wear a Medic-Alert bracelet.
22. Advise patient to avoid alcohol, tonic, water.
Complications: Aspiration, complications of decreased mobility, respiratory failure.
