Pharmacology · chapter 10 · Drugs to Treat Myasthenia Gravis and Alzheimer’s Disease
Introduction to Myasthenia Gravis
The 14 things this section of the textbook says that you are most likely to be asked about — quoted word for word, not retold. Then 6 practice questions with the reasoning.
Key points
What myasthenia gravis is
Myasthenia gravis (MG) is a progressive autoimmune neuromuscular disorder characterized by fluctuating muscle weakness and the onset of rapid fatigue.
Ocular and generalized forms
The ocular form causes muscle weakness only in the eyelids and extraocular muscles. The generalized form includes a combination of extremities, esophageal and respiratory muscles, and the aforementioned ocular form.
Antibodies destroy acetylcholine receptors
According to the National Institute of Neurological Disorders and Stroke (2023b), individuals with MG lack a significant number of functional receptor sites (as much as 70%–90%) because the individual’s immune system produces antibodies (protein produced in response to a specific antigen) that block, alter, or destroy the receptors for acetylcholine at the NMJ.
Why the muscles are weak
In addition to fewer receptor sites, the synaptic space widens, which impairs signal transmission. The outcome of these changes is the inability of muscles to contract, resulting in muscle weakness.
Focus of the nursing assessment
The assessment of the neurological system is the primary focus: the client’s muscle strength, tone, and coordination should be examined; sensation and extraocular eye movements should be evaluated.
Most sensitive diagnostic test
A single-fiber electromyography (EMG) test can detect delayed or failed neuromuscular transmission in muscle fibers that are supplied by a single nerve fiber. The EMG is considered the most sensitive test in diagnosing MG.
Ptosis and diplopia come first
Ptosis (drooping of the eyelid) and diplopia (double vision) are the presenting symptoms in half of the clients diagnosed with MG.
Strongest in the morning
The cardinal feature of early MG is fluctuating skeletal muscle weakness and muscle fatigue. Many times, muscle strength is strongest in the morning hours and will decrease throughout the day.
Triggers that worsen symptoms
Several factors can exacerbate MG symptoms, including emotional stress, infection, surgery, aminoglycosides, hypo- or hyperthyroidism, hormonal fluctuations, and an increase in body temperature.
Myasthenic crisis is an emergency
A sudden exacerbation of symptoms is known as a myasthenic crisis, which is considered a medical emergency because fatal consequences can result. If respiratory muscles are affected, ventilation will be compromised.
Dysphagia, choking and aspiration
The impairment of these muscles will result in dysphagia (difficulty swallowing) and lead to choking and/or aspiration.
How AChE inhibitors work
The presynaptic neuron continues to release ACh, while the synapse accumulates ACh because it is not broken down. This results in the cholinergic receptors being stimulated for a prolonged period of time.
Taper glucocorticoids gradually
When the client’s symptoms are under control, the glucocorticoids should be gradually titrated and discontinued.
Azathioprine boxed warning
Azathioprine is given orally. It does have a black box warning related to the risk of malignancy (DailyMed, Azathioprine, 2022).
Terms to know
- myasthenic crisis
- A sudden exacerbation of symptoms is known as a myasthenic crisis, which is considered a medical emergency because fatal consequences can result.
- seronegative
- However, some clients with MG will have neither of these antibodies, a condition termed seronegative (negative antibody) myasthenia gravis.
- dysarthria
- This is referred to as dysarthria (difficulty speaking).
- acetylcholinesterase (AChE) inhibitors
- The main pharmacological class to treat MG is acetylcholinesterase (AChE) inhibitors.
Practice questions
Stuck on select-all-that-apply? How to take them one option at a time.
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Every question here, with the answer
A client with myasthenia gravis develops a fever from a respiratory infection and reports sudden, severe weakness. Which assessment is the nurse's priority?
- Bowel sounds
- Ability to read small print
- Grip strength in both hands
- Respiratory effort and ventilation
Answer: Respiratory effort and ventilation
A sudden exacerbation is a myasthenic crisis, a medical emergency, and if respiratory muscles are affected ventilation is compromised. Grip strength, vision and bowel sounds do not address the life-threatening risk.
A nurse is teaching a client with myasthenia gravis about factors that can worsen symptoms. Which factors should the nurse include? Select all that apply.
- An increase in body temperature
- A regular sleep schedule
- Surgery
- Infection
- Emotional stress
Answer: An increase in body temperature, Surgery, Infection, Emotional stress
Emotional stress, infection, surgery and a rise in body temperature are all listed as factors that exacerbate MG. A regular sleep schedule is not a trigger.
A client with myasthenia gravis needs to go to physical therapy and a diagnostic test today. When should the nurse schedule the more demanding activity?
- Late afternoon
- In the morning
- Evening, after dinner
- Right before bedtime
Answer: In the morning
Muscle strength in MG is often strongest in the morning and decreases throughout the day. Scheduling demanding activity later in the day meets the client at their weakest.
A client with generalized myasthenia gravis coughs and chokes while eating lunch. Which complication is the nurse most concerned about?
- Hypertension
- Aspiration
- Diplopia
- Ptosis
Answer: Aspiration
When chewing and swallowing muscles are affected, dysphagia can lead to choking and aspiration. Diplopia and ptosis are eye symptoms, and hypertension is not linked to swallowing.
A nurse is admitting a client with suspected myasthenia gravis. Which findings are consistent with the disease? Select all that apply.
- Loss of sensation in both feet
- Drooping of the eyelid
- Double vision
- Slurred speech after a few minutes of talking that clears with rest
- Weakness that is worst right after waking and improves by evening
Answer: Drooping of the eyelid, Double vision, Slurred speech after a few minutes of talking that clears with rest
Ptosis and diplopia are presenting symptoms in half of clients, and speech that slurs with constant talking and clears after rest is typical. MG weakness is usually strongest in the morning and worsens during the day, and it affects muscle strength, not sensation.
A client with myasthenia gravis whose symptoms are now controlled asks whether the high-dose glucocorticoid can be stopped today. Which response by the nurse is correct?
- The dose should be gradually titrated down before it is discontinued.
- It must be continued at the same high dose for life.
- It should be switched to an aminoglycoside.
- Yes, it can be stopped at once because symptoms are gone.
Answer: The dose should be gradually titrated down before it is discontinued.
Once symptoms are controlled, glucocorticoids should be gradually titrated and discontinued, not stopped abruptly or continued at high dose. Aminoglycosides are listed as a factor that can worsen MG.
Where every quote comes from
Section 10.1 Introduction to Myasthenia Gravis of Pharmacology for Nurses by Tina Barbour-Taylor, Leah Mueller (Sabato), Donna Paris, Dorie Weaver, OpenStax, 2024. Read the whole section free at openstax.org.
The textbook is licensed under CC BY-NC-SA 4.0. This page quotes it word for word and adds the headings, the order and the practice questions; references to the book's figures and stray spaces left by its formatting are removed. The page is shared under the same licence. Nothing here is sold.