Med-Surg: Chapter 38: Myasthenia Gravis

Question 1

Myasthenia Gravis

Answer 1

-autoimmune neuromuscular junction disorder
-results in the bodies immune system attacking healthy cells
-is a motor disorder characterized by fluctuating, localized skeletal muscle weakness and fatigue
-myasthenia= muscle weakness
-gravis= grave
>grave muscle weakness

Question 2

What is Myasthenia Gravis Caused by?

Answer 2

antibodies that are directed toward skeletal muscle nicotinic ACh receptors and muscle-specific kinase (MuSK)

Question 3

How is this disorder characterized?

Answer 3

this chronic neurological disorder is characterized by skeletal muscle weakness that may fluctuate throughout the day
-myasthenia = muscle weakness
-gravis= “grave”
> name = grave muscle weakness

Question 4

Epidemiology of Myasthenia Gravis

Answer 4

• is a motor disorder characterized fluctuating, localized skeletal muscle weakness and fatigue
• it is an acquired autoimmune disease in which antibodies bind to the ACh receptors on the muscle membrane
• may be made worse by or induced by penicillamine (Cuprimine), used in the treatment of rheumatoid arthritis; but usually idiopathic

Question 5

The Course of the Disease

Answer 5

vary from mild, with ocular symptoms of ptosis (drooping eyelids) and diplopia (double vision)
to severe cases with generalized weakness and respiratory involvement

Question 6

Ptosis

Answer 6

drooping eyelids

Question 7

Diplopia

Answer 7

double vision

-result of extraocular muscle weakness

Question 8

Pathophysiology

Answer 8

> In normal nerve transmission: ACh is produced and secreted in the terminal ends of the motor nerves. Acetylcholine crosses the synaptic clefts and attaches to ACh receptors embedded in the folds of the postsynaptic membrane; this ACh-AChR binding results in depolarization of the end plate. Muscle membrane depolarization quickly occurs, resulting in skeletal muscle contraction
In MG, circulating anti-AChR antibodies bind with the AChR, resulting complement-mediated destruction of the receptor sites. Postsynaptic membranes lose their folds, and ACh binding is blocked. Sensitivity to normal amounts of ACh is diminished with reduction of initiating depolarization and therefore muscle contraction; results in skeletal muscle weakness and fatigability
-in MG, there is an adequate amount of ACh released, but postsynaptic receptor sites are not available

Question 9

Thymus Gland

Answer 9

organ of the immune system that produces T cells or T lymphocytes

• 70% of pts with MG have thymic hyperplasia (enlarged thymus), or 10% have thymoma (tumor of the thymus gland)
• thymus gland may have give flawed instructions to developing immune cells, resulting in the development of AChR antibodies

Question 10

Clinical Manifestations

Answer 10

• categorized into ocular, bulbar, or personalized presentation
• muscular weakness and fatigue
• ptosis (drooping eyelid)
• diplopia (double vision)
• bulbar symptoms: difficulty phonation (utterance in speech), chewing, and swallowing
• trunk and limb weakness
• muscles of the neck, deltoids, triceps, wrists, fingers, and ankles commonly affected

> weakness varies across the day but generally worsens late in the day, and clinical manifestations worsen with sustained muscle use
patients may complain of difficulty with completing activities of daily living (ADLs), like bathing and dressing

Question 11

Bulbar Symptoms

Answer 11

• clinical manifestations involving the cranial nerves
• medulla is shaped like a bulb, and linked to the term bulbar
• manifestations include: difficulty with phonation (utterance in speech), chewing, and swallowing

Question 12

Diagnosis

Answer 12

based on clinical assessment and analysis of tests: serological tests, electromyography, and edrophonium (Tensilon) test

Question 13

Serological Testing

Answer 13

• an assay for AChR antibodies
• the AChR-binding antibody assay is specific, and positive antibody studies verify MG in the presence of a clinical picture that is consistent with MG

Question 14

Repetitive Nerve Stimulation

Answer 14

diagnostic tool used to evaluate neuromuscular transmission and measure muscle action potential after repeated nerve stimulations
-in MG, there is decreased muscle response with repetitive stimulation

Question 15

Single-Fiber Electromyography

Answer 15

most sensitive diagnostic tool for detecting an abnormality in neuromuscular transmission
-requires needles to be placed in the muscle to measure electrical activity
>in normal, the recording shows two evoked responses from two muscle fibers firing, with minimal fluctuation of the interval between the two; fluctuation is called a “jitter” and is due to the variable time required for neuromuscular transmission from discharge to discharge
-in MG, there is increased “jitter”

Question 16

Tensilon (Edrophonium) Test

Answer 16

• diagnostic test performed by provider
• up to 10 mg of edrophonium, a short-acting anticholinesterase medication, is administered via IV push
• Edrophonium temporarily improves neuromuscular transmission by inhibiting AChE, which is the enzyme that degrades ACh after binding to the AChR site
• Before administration, the provider focuses on a weak group of muscles, such as the ocular muscles; an initial dose of 2 mg is given while the patient has sustained visual focus on an object; the provider assesses for improvement of the ptosis; if no affect is observed, additional doses of 3 and 5 mg are administered at 1-minute intervals; improvement of muscle weakness at 2 to 5 minutes followed by a return to baseline over the next 5 minutes = a positive test
• atropine should be readily available to reverse any severe bradycardia that may occur during the test

Question 17

Endrophonium

Answer 17

a rapid-acting AChE inhibitor

• this leads to increased levels of ACh at the neuromuscular junction, leading to improved muscle strength in patients with myasthenia; unfortunately this action is not specific to the neuromuscular junction, and ACh accumulates in the parasympathetic ANS as well; accounts for majority of side effects like bronchospasm, bradycardia, and diarrhea
• increased stimulation of the muscarinic receptors leads to bradycardia and bronchospasm in the lungs

Question 18

Atropine

Answer 18

muscarinic blocker

• used to reverse the side effects of edrophonium
• it works only in the ANS so it will not interfere with the activity of the neuromuscular junction
• atropine should be available to reverse any severe bradycardia that may occur during edrophonium testing

Question 19

Chest Computed Tomography Scan (CT)

Answer 19

routinely performed to evaluate for thymoma

Question 20

Treatment

Answer 20

• individualized
• aimed at symptomatic treatment to increase the availability of ACh, immunosuppression, approaches to alter the immunopathogenic mechanism underlying MG, and immunomodulary effect with thymectomy

Question 21

Mediations

Answer 21

• Pyridostigmine (Mestinon)
• Neostigmine (Prostigmin)
• Immunotherapy

Question 22

Pyridostigmine (Mestinon)

Answer 22

is a reversible inhibitor of AChE
-improves neuromuscular transmission by increasing ACh stimulation of the AChRs that are available
-accepted initial tx of choice
-muscarinic side effects: stomach cramps, diarrhea, increased secretions, nausea, bradycardia, and muscle twitches
>must be administered exactly as prescribed to maintain optimal muscle strength
>take 30 to 60 minutes before meals to minimize difficulty with swallowing and chewing

Question 23

Neostigmine (Prostigmin)

Answer 23

shorter-acting AChE inhibitor

• administered IV when oral route not available
• Side Effects: bradycardia and cardiac dysrhythmias
• some policies require dual IV access incase the first site infiltrates
• the provider determines the proper dose conversion to oral pyridostigmine (Mestinon) when the patient is ready to resume taking medications orally
• the nurse administers pyridostigmine 1 hour before stopping the IV medication (Neostigmine)

Question 24

Medication: Pyridostigmine (Mestinon)

Answer 24

anticholinesterase inhibitor

• oral tablet, liquid, or sustained release
• 60 mg tablets while awake
• should be administered exactly at prescribed hour
• administer 30 to 60 minutes before meal
• monitor for increased secretions, muscle cramps, and diarrhea
• if patient on IV Neostigmine, give this 1 hour before stopping IV

Question 25

Medication: Prednisone (Deltasone, Prednicot)

Answer 25

corticosteroid
-provide education about side effects of steroids:
>immunosuppression, GI bleed, hyperglycemia, weight gain, truncal obesity, and sleep disturbance
-monitor blood glucose levels; may require insulin coverage
-confer with provider to provide patient with calcium and vitamin D supplementation to decrease bone loss

Question 26

Immunotherapy

Answer 26

these medications initiated when AChE inhibitors are not adequate in moderately severe MG

• Prednisone (Main Med in this category)
• Azathioprine (Imuran)
• Cyclosporine
• Mycophenolate mofetil (CellCept)
• Cyclophosphamide (Cytoxan)

Question 27

Immunotherapy: Azathioprine

Answer 27

steroid-sparing medication

-inhibits T-cell and B-cell proliferation through interaction with purine metabolism and nucleic acid synthesis

Question 28

Immunotherapy: Cyclosporine

Answer 28

inhibits T helper cell-mediated synthesis of cytokines and other T helper cell-mediated immune reactions

Question 29

Immunotherapy: Mycophenolate Mofetil (CellCept)

Answer 29

suppresses both T-cell ad B-cell proliferation

-adverse effects: diarrhea, anemia, leukopenia, and infections

Question 30

Immunotherapy: Cyclophosphamide (Cytoxan)

Answer 30

chemotherapeutic agent

• at high doses, used to ablate (destroy) bone marrow and allow the patients endogenous stem cells to repopulate the immune system with new lymphocytes
• allows patient’s immune system to “reboot”

Question 31

Medications that are contraindicated

Answer 31

• some antibiotics
• calcium channel blockers
• D-penicillamine
• magnesium
• aside from IV magnesium sulfate, nurses need to be aware of certain antacids and laxatives that also contain magnesium b/c they should be avoided in patients with MG

> antibiotics (streptomycin, polymyxin) exhibit a nondepolarizing blocking action on neuromuscular transmission
Calcium-channel blockers and magnesium block calcium, which is necessary for normal muscular transmission

Question 32

Additional Therapies

Answer 32

• IV immunoglobulin (IVIG)

- Plasmapheresis

Question 33

IV Immunoglobulin (IVIG)

Answer 33

quicker onset of action

• inactivates abnormal autoantibodies and suppresses T-cell function
• administered slowly, and rate titrated
• vital signs checked frequently
• monitored for flu-like symptoms (e.g fever, headache, chills, myalgia)
• renal functions including BUN and creatinine monitor prior to initial infusion and periodically

Question 34

Plasmapheresis

Answer 34

requires insertion of a large-bore dual-lumen catheter
-the patients blood is removed through the arterial lumen and circulated through the plasmapheresis machine, which removes antibodies that block AChR function
-goal of treatment is to improve muscle strength
-anticoagulation is required to prevent clotting in the extracorporeal blood during an apheresis procedure (a procedure that involves removing whole blood and separating the blood into individual components so that one particular component can be removed)
>Citrate anticoagulant of choice
-the solid blood components, RBCs, WBC, and platelets are returned through the venous lumen with normal saline and albumin; total of 7 treatments usually ordered
-because plasmapheresis involves removal of plasma, mediations in the plasma may be removed; prior to tx consult with provider to determine if any medications should be held; antihypertensives may increase the chance of hypotension during treatment; also potential to for plasmapheresis to affect therapeutic levels of medication
-pts monitored for blood clotting following each session b/c the procedure can remove coagulation factors in the blood

Question 35

Plasmapheresis and Hypocalcemia

Answer 35

may experience paresthesias from citrate-induced hypocalcemia and hypotension may occur at the start of the exchange
-asked to report any numbness or tingling, especially around the lips; indicative of hypocalcemia; b/c the citrate binds with calcium to effectively prevent clotting, the patient has an increased risk of hypocalcemia
-the ionized calcium level decreases in the pt as a result of cirrate infusion, the removal of calcium in the patients wasted plasma, and the calcium-binding properties of albumin
-can be prevented by adding calcium to the replacement fluid, 5% albumin, or slowing down the infusion of the citrate during the procedure
>if citrate reactions not treated, they can progress from paresthesia, vibration sensation, nausea/vomiting, and diarrhea, to hypotension, chest tightness, tetany, and cardiac arrhythmias

Question 36

Plasmapheresis: Hypovolemia

Answer 36

-during plasmapheresis fluid shifts are caused by removing plasma and replacing the plasma with substitute fluids or 5% albumin, and some may experience nausea and vomiting b/c of fluid shifts and electrolyte imbalances
-the change in intravascular volume and the dilutional effects may cause hypovolemia
-manifestations of hypovolemia: dizziness, light-headedness, nausea, diaphoresis, tachycardia, and hypotension
>can be treated by pausing the procedure, placing the patient in Trendelenburg position if not contraindicated, and administering a saline bolus of fluids

Question 37

Plasmapheresis: Vasovagal reaction

Answer 37

may experience pallor, sweating, diaphoresis, nausea/vomiting, hypotension, and bradycardia
>treatment same as hypovolemia
-electrolytes potassium and calcium need to be monitored for patients receiving plasmapheresis

Question 38

Surgical Management: Thymectomy

Answer 38

• usually performed within first 3 years of diagnosis
• always performed for pts with thymoma
• transsternal extended thymectomy
• require IV neostigmine b/c of NPO status and management in an intensive care unit following surgery
• intravenous neostigmine is required to maintain muscle strength and respiratory function

Question 39

Complications

Answer 39

• Myasthenic Crisis

- Cholinergic Crisis

Question 40

Myasthenia Crisis

Answer 40

exacerbation of MG weakness that provokes an acute episode of respiratory failure that is often caused by a respiratory infection from viral or bacterial agents

• weakness may involve the respiratory or bulbar muscles and may affect the patients ability to protect the airway
• tachycardia, flaccid muscles, and pale and cool skin
• usually lasts for 2 weeks
• IV immunoglobulin or Plasmapheresis used to manage the patient throughout the crisis

Question 41

Cholinergic Crisis

Answer 41

due to excessive anticholinesterase medication and is secondary to the patient taking too much of the prescribed MG medication
-muscle bradycardia, fasciculations (muscle twitch), sweating, pallor, excessive secretions, and small pupils

Question 42

How to determine between Myasthenia Crisis and Cholinergic Crisis?

Answer 42

The Tensilon (edrophonium) test

• when Tensilon is administered, if the patient demonstrates muscle strength improvement, = myasthenia crisis
• if administered and demonstrates fasciculations and muscle weakness, including respiratory muscles,= cholinergic crisis; anticholinesterase medications temporarily d/c in a cholinergic crisis

Question 43

Diet

Answer 43

-benefit from evaluation of a speech language pathologist and registered dietician
-b/c of the weakness of the oropharyngeal muscles, the patient my have difficulty chewing and swallowing which increases risk for aspiration
>diet may include thickened liquids or enteral tube feedings

Question 44

Nursing Management: Assessment and Analysis

Answer 44

clinical manifestations include respiratory deterioration and muscular weakness

• nurse performs neurological assessment, including detailed cranial nerve assessment
• assesses motor strength to identify muscle weakness
• b/c of potential for respiratory weakness, a bedside test known as the vital capacity is performed; vital capacity is the maximum amount of air exhaled following maximal inhalation; normal value of 65 mL/kg; when falls below 15 mL/kg or 1 L, respiratory deterioration may progress rapidly and mechanical ventilation will be required

> MG is assessed for following manifestations

• muscle weakness that increases over the course of the day
• fatigue
• Ptosis
• Diplopia
• Dysphagia
• Dysarthria

Question 45

In patients with MG it is important to monitor what?

Answer 45

Vital Capacity

• pulse ox not helpful
• obtain ABGs

Question 46

Nursing Interventions: Assessment

Answer 46

> Assess breath sounds and observe the patient’s respiratory effort

• obtain vital capacity per order; usually obtained immediately prior to a dose of pyridostigmine to obtain a trough value and then 1-hour post-dose to value peak effect
• if value below 1 L = at risk for respiratory compromise; notify provider; respiratory deterioration may lead to respiratory arrest; often require intubation and mechanical ventilation in an ICU

> Vital Capacity Measurement

• if value below 1 L, notify provider
• in MG, patient develops weakness of the diaphragm and intercostal muscles; weakness of respiratory muscles results in diminished forced vital capacity

> Cranial Nerves
-bulbar symptoms first to appear in about 16% of MG patients and place patient at risk for aspiration due to difficulty swallowing

> Dysphagia
-weakness of the oropharyngeal muscles places the patient at risk for dysarthria and dysphagia

> Nutritional intake, intake and output, and daily weight

• cranial nerve weakness can make it difficult for the patient to chew and swallow
• may become fatigued during the meal

> Dysarthria

• patients may have a nasal quality to the speech and be at risk for aspiration b/c of weakness of these muscles
• due to impairment of cranial nerves

Question 47

Nursing Actions

Answer 47

> Administer medications at prescribed times and prior to activities requiring swallowing

• Pyridostigmine must be administered exactly at the prescribed hour to maintain optimal muscle strength
• take Pyridostigmine 30 to 60 minutes before meals to minimize difficulty with chewing and swallowing

> Elevate the head of the patient’s bed with eating or drinking
-weakness of the oropharyngeal muscles increases the risk of aspiration, and elevating the head of the bed may decrease aspiration

> Establish effective communication method with the patient
-consult with speech language pathology to obtain a picture communication board b/c verbal communication is impaired by dysarthria

> Plan meals when medications are at peak levels

• timing the meals with peak medication levels decreases the risk of aspiration
• small, frequent meals will help maintain caloric intake
• weight loss may result from poor nutritional intake

> Offer soft foods and thickened liquids as recommended by speech language pathologist
-a temporary feeding tube may be necessary if swallowing is impaired or if the patient deteriorates and requires intubation and mechanical ventilation

> Plan for rest periods between activities of daily living
-use energy conservation techniques, such as sitting while activities of daily living are completed, to minimize fatigue and muscle weakness

Question 48

Teaching

Answer 48

> Importance of taking medications as prescribed
-teach the patient to adhere to the medication schedule at home b/c swallowing may be impaired if eating, drinking, brushing teeth, and other activities are not performed at peak levels of the medications

> Educate the patient to keep medication with them at all time; spare doses should be kept at the place of employment and in the car; When the patient travels, mediation should remain with the patient in carry-out luggage
-patient should not miss a dose of pyridostigmine bromide b/c this can lead to muscular weakness

> Purchase a Medical Alert bracelet and wear it daily
-in the event of an emergency, the patient’s diagnosis may be rapidly identifiable by emergency medical providers

> Avoid public places such as theaters or concerts in the winter where there are large gatherings of people
-patient may be exposed to colds and the flu where there are large gathering of people, and increases risk of exacerbation

> Obtain vaccines to prevent the flu and pneumonia

• vaccines decrease the risk of infection
• respiratory infections may lead to myasthenic crisis that require hospitalization

> Prevent fatigue with frequent rest periods. Recognize physical limits, and plan activities during peak energy periods
-the risk of injury is decreased when activities are scheduled during peak times of medications

> Do not take any over-the-counter preparations w/o first checking with provider
-OC products may have ingredients that are contraindicated in MG

> Inform the patient and family about resources, such as Myasthenia Gravis Foundation of America

Question 49

Evaluating Care Outcomes

Answer 49

• may be successfully managed with cholinesterase inhibitors
• patient and family made aware of crisis and seek medical attention quickly
• patient education; adherence to prescribed medications and treatment plan, patients are able to actively participate in family activities and a career