Myasthenia Gravis – Symptoms and Treatment

Myasthenia Gravis

Welcome to this video tutorial on myasthenia gravis.

Myasthenia gravis (MG) literally means…

			 “grave muscle weakness”

Effective muscle contraction is dependent on adequate amounts of the neuromuscular transmitter ACh binding to acetylcholine receptors to initiate a muscle contraction.

MG is a chronic disease that results from an autoimmune response that destroys ACh receptors at the neuromuscular junction.

Muscle weakness occurs when ACh cannot activate enough receptor sites at the neuromuscular junction.

The onset of myasthenia gravis (MG) is usually gradual & the course of the disease highly variable.

It can occur at any age, but usually affects women at 20-30 and men at 60-70 years of age.

SIGNS & SYMPTOMS of MG involve: Weakness & fatigue of selected voluntary muscles

     The hallmark signs are diplopia (double vision) & ptosis (drooping eyelid)
Slurred speech
Difficulty chewing & swallowing
Weakness in arms & legs
Chronic muscle fatigue
Difficulty breathing
Early on in the disease, symptoms are relieved easily with rest,
but as the disease progresses, fatigue becomes evident with less & less exertion.

Several ways to diagnose Myasthenia Gravis

     Tensilon Test - edrophonium, a short-acting anticholinesterase, is given IV –
the patient with MG experiences a significant but brief increase in muscle strength
in previously weakened muscles – this response is a positive result.
Blood test – ACh receptor antibody titers will be elevated.
Electromyogram (EMG) – detects delay or failure in muscle fibers that are
repetitively stimulated.
Thoracic MRI – shows the thymus gland enlarged/abnormal

TREATMENT

Although MG has no known cure, it can generally be controlled with therapies to reduce & improve muscle weakness.

     Indirect-acting cholinergics (anticholinesterase agents) -
improve neuromuscular transmission & increase muscle strength.
- Neostigmine (Prostigmin) & Pyridostigmine
Immunosuppressive drugs – improve muscle strength by suppressing the
production of abnormal antibodies (but may cause major side effects).
- Prednisone, azathioprine (Imuran), cyclosporin, tacrolimus
Plasmapheresis – the patient’s plasma is removed and replaced with albumin
or fresh frozen plasma & the ACh receptor antibodies are removed in the
process – improvements are usually dramatic, but temporary.
Thymectomy – surgical removal of the thymus gland – results in symptom remission
in about 40% of patients, possibly due to the re-balancing of the immune system

Patients with MG are susceptible to two crisis situations that are both characterized by respiratory difficulty or failure.

Myasthenic Crisis

     An acute exacerbation of the disease process & may occur in
response to stress, trauma, or infection.
The muscles that control breathing & swallowing can weaken to the point
of life-threatening levels and assisted ventilation is usually required.
When this happens, additional anticholinesterase medications are given.

Cholinergic crisis

Occurs when cholinergic drugs have reached a toxic level & cause
over-stimulation of the PSNS - anticholinesterase drugs are stopped
& atropine (an anticholinergic drug) is given.
Pt has profound weakness, copious respiratory secretions & respiratory
failure, which may require intubation & ventilation.

Is it a myasthenic or cholinergic crisis?

 

     If signs & symptoms begin about 1 hour after an anticholinesterase drug
was given – it is most likely a cholinergic crisis (too much drug).
Signs & symptoms beginning 3 or more hours after medication is given is more
likely to be a myasthenic crisis (too little drug).
A Tensilon test can be done if unable to differentiate between the
two conditions.

Educating the patient & family about self-care is foundational in the management of MG.

     Wear medical alert ID at all times
Balance rest & activity throughout the day – do not overexert yourself
& plan for extra periods of rest.
Modify your diet as needed in response to swallowing problems
(usually a soft diet, eating slowly & taking small bites).
Be aware of disease response to stress, infection, temperature extremes,
& hormonal swings – avoid stress & extreme heat.
Wear practical shoes for easier walking & maintaining balance.
Take all anticholinesterase drugs with food or milk to prevent
stomach upset.
Inform your doctor of any other medications being taken - Rx, OTC or
herbs - as many can compromise neuromuscular transmission & will worsen
disease symptoms.

Thank you for watching this video tutorial about myasthenia gravis.

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by Mometrix Test Preparation | Last Updated: August 15, 2019