Pathophysiology: Nerve impulse transmissions are defected. The body forms autoantibodies against ACh receptors. This blocks AChR. This causes a reduced about of receptor sites, which causes a reduced transmission of nerve impulses. This means that the muscular depolarization is not achieved and incomplete.
- Chronic, progressive disorder of the PNS which affects transmission of nerve impulses to muscles
- Insufficient secretion of acetylcholine
- Excessive secretion of cholinesterase
- Onset often caused by precipitating factors (stress, hormone disturbance, infection, trauma, temperature)
- AKA “Triggers”
- Myasthenia Gravis
- Diplopia (double vision)
- Ptosis (drooping eyelid)
- Especially of respiratory muscles (diaphragm and intercostals)
- Monitor respiratory status
- Abnormal ABG
- Breath sounds
- Cholinergic Crisis: Severe muscle weakness due to overmedication
- Muscle cramps
- Bronchial spasm
- N/V, diarrhea
- Blurred vision
- Withhold medication
- Administer antidote
- Ventilatory support
- Myasthenic Crisis: Acute exacerbation of disease, caused by insufficient medication dosage
- Sudden severe motor weakness
- Risk of respiratory failure
- Increased pulse, respirations, and BP
- Hypoxia and cyanosis
- Bowel and bladder dysfunction
- Increase medication
- Ventilatory Support
- Cholinesterase Inhibitors
- Net increase of Acetylcholine activity at the synapse
- i.e. – Physostigmine
- Tensilon test
- Used to confirm diagnosis
- Client at risk of VFib and cardiac arrest – have crash cart available
- May make Cholinergic Crisis worse – have Atropine available
- Monitor respiratory status
- Maintain suction and emergency equipment
- Ensure proper medication dosing
- Monitor feeding and ensure proper nutrition
- Schedule medication 30-40 minutes prior to meals
- Provide adequate eye care if ptosis
- Identify and avoid triggers
- Temperature extremes, emotional stress, drugs, alcohol, and exposure to infection
- Signs of cholinergic and myasthenic crisis
Cornell Note-Taking System Instructions:
- Record: During the lecture, use the note-taking column to record the lecture using telegraphic sentences.
- Questions: As soon after class as possible, formulate questions based onthe notes in the right-hand column. Writing questions helps to clarifymeanings, reveal relationships, establish continuity, and strengthenmemory. Also, the writing of questions sets up a perfect stage for exam-studying later.
- Recite: Cover the note-taking column with a sheet of paper. Then, looking at the questions or cue-words in the question and cue column only, say aloud, in your own words, the answers to the questions, facts, or ideas indicated by the cue-words.
- Reflect: Reflect on the material by asking yourself questions, for example: “What’s the significance of these facts? What principle are they based on? How can I apply them? How do they fit in with what I already know? What’s beyond them?
- Review: Spend at least ten minutes every week reviewing all your previous notes. If you do, you’ll retain a great deal for current use, as well as, for the exam.
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Okay, let’s talk about Myasthenia Gravis. This is also a progressive disease, but the good news for this compared to MS is that medications these days are really able to control the issues and these patients can live normal lives.
So Myasthenia Gravis is also a chronic, progressive disorder of the nervous system. In this case it affects transmission of nerve impulses peripherally to muscles. This is mostly skeletal muscles, but also some smooth muscle involvement, especially in the gut. It is often exacerbated by precipitating factors or triggers. The most common triggers are stress and temperature extremes. It can also be triggered by hormone disturbances, infection, and trauma. Now, the primary neurotransmitter affected in myasthenia gravis is acetylcholine – so let’s look at what happens physiologically.
If you remember from the impulse transmission lesson, neurotransmitters help to transmit nerve impulses across the synapses between neurons and their target organs. Acetylcholine is one of those neurotransmitters and it is the primary neurotransmitter responsible for muscle movement – skeletal and smooth. In myasthenia gravis, what we see is a decrease in acetylcholine activity at the synapses. That’s due to insufficient secretion of acetylcholine from the neuron as well as excessive secretion of cholinesterase. Remember cholinesterase is the enzyme responsible for deactivating the acetylcholine. So not only are we not secreting enough of it, but we’re also deactivating it way more than usual. So overall there’s much less acetylcholine working at the synapse, and therefore the patient struggles with muscle movement.
So what we see in our patients is all related to weak muscles that can’t contract appropriately. We see double vision and eyelid drooping because of weakened muscles in the eyes and eyelids. We will see generalized weakness and fatigue. Now this is different than MS. In MS they have spastic movements because the impulses are slower and jumpy. In Myasthenia gravis, once the impulse is transmitted it’s smooth, it’s just getting it transmitted in the first place that’s the problem – so they struggle with any muscle movements in general. That includes the muscles involved in breathing like the diaphragm and intercostal muscles, so we actually see these patients at risk for respiratory distress because of that weakness. Some possible complications we’ll talk about are cholinergic crisis and myasthenic crisis. So let’s look at those one at a time.
When we treat myasthenia gravis, we will give medications to increase acetylcholine activity at the synapse. But what can happen is that we could possibly overmedicate and get excessive acetylcholine activity – that leads to a cholinergic crisis. What happens is that the muscles actually stop responding to the bombardment of acetylcholine, they become desensitized and you see severe muscle weakness. They can get anything from cramps to full paralysis. We’ll see nausea, vomiting, diarrhea because of the involvement of smooth muscle in the gut. We will see hypotension, bradycardia, and blurred vision. But again, the biggest risk here comes with the effects on the respiratory system. They could have bronchial spasm or go into respiratory failure because they can’t use those muscles. So first and foremost we will withhold any more doses of that medication, then we will give an antidote. So this is cholinergic crisis, so the antidote is anti-cholinergics like Atropine. However, sometimes you just have to wait for the medication to clear their system, so we will be sure to support their airway and breathing with a ventilator until the crisis is over.
The second complication is the opposite problem. Myasthenic crisis is an acute exacerbation of myasthenia gravis due to insufficient medication dosage. I’ve actually seen someone fall into myasthenic crisis because they missed one dose of their medication. Without it, you see sudden severe motor weakness. Their heart rate, respiratory rate, and BP will increase trying to compensate for this weakness. You’ll see bowel and bladder incontinence and again this super high risk for respiratory failure. You may see super shallow breathing and hypoxia or even cyanosis. So we need to give medications and possibly increase their dose. We give cholinesterase inhibitors primarily, which we’ll talk about in a second. And again, support their ventilation if needed while we sort out the issue.
So our primary medication for management of myasthenia gravis is cholinesterase inhibitors. Remember we said myasthenia gravis is decreased secretion of acetylcholine but also excessive secretion of cholinesterase – the enzyme that deactivates acetylcholine. If we can inhibit that enzyme, we will allow more acetylcholine activity at the synapse. The most common example is Physostigmine. Now, we will also do something called the Tensilon test to confirm the diagnosis. It’s a strong cholinesterase inhibitor. If the patient gets better, you know it’s myasthenia gravis. Now – an important note here – this could actually make cholinergic crisis WORSE and it puts the patient at risk for VFib or Cardiac Arrest – so make sure you have emergency equipment and atropine at the bedside before giving the Tensilon.
Priority nursing concepts for a patient with myasthenia gravis are safety, comfort, and patient education. We need to make sure we’re monitoring and protecting their airway, but also preventing complications like cholinergic or myasthenic crisis by making sure their medications are appropriate and monitoring for symptoms. We want to make sure they’re comfortable because they can get cramping and fatigue. And patient education is a priority so that they understand the importance of taking their medications, identifying and avoiding triggers, and signs and symptoms of crisis to report to their provider ASAP. Make sure you check out the care plan attached to this lesson for more detailed nursing interventions and rationales.
So remember that myasthenia gravis is a progressive disorder that decreases the transmission of impulses to muscles because of decreased acetylcholine activity in the synapse. That is caused by insufficient secretion of acetylcholine or excessive cholinesterase activity. It can be brought on by triggers like stress and temperature extremes so make sure patients can identify their triggers and avoid them. We need to prioritize respiratory support, especially if the patient is in crisis – but ultimately preventing cholinergic and myasthenic crisis would be best since they can both be life-threatening.
Now, we know some people struggle to keep this separate from Multiple Sclerosis. Here’s a quick way to remember. Multiple Sclerosis – MS – Myelin Sheath. Myasthenia Gravis – MG – Muscles Gone. So I hope that helps. Make sure you check out the resources attached to this lesson to learn more! Let us know if you have any questions! And as always, Happy Nursing!