Myasthenia Gravis

• Myasthenia Gravis literally means grave muscle weakness.
• It is an autoimmune neuromuscular disease.
• The disease leads to fluctuating skeletal muscle weakness and fatigability.
• Myasthenia Gravis results from failure of nerve transmission at the neuromuscular junction.
• Failure of nerve transmission is caused by inadequate release of acetylcholine or inadequate response of muscle fibers to acetylcholine.
• Voluntary muscles are affected, especially those innervated by the cranial nerves.
• There are three types of muscles affected in MG: ocular, bulbar, and generalized.
• Ocular MG affects only eye and lid muscles.
• Bulbar MG affects muscles for breathing, swallowing, and speaking.
• Generalized MG affects ocular, bulbar, neck, and limb muscles, and is the most common.
• The exact cause of Myasthenia Gravis is unknown.
• It is characterized by a decrease in Ach secretion by the motor end plate.
• Increased acetylcholinesterase, the enzyme that destroys Ach, is present at the nerve endings.
• Autoimmune diseases like thymoma can be a cause.
• Normally, nerve impulses travel down the nerve, the nerve endings release a neurotransmitter substance, Ach travels through the neuromuscular junction before binding to acetylcholine receptors and activating muscle contraction.
• Myasthenia Gravis pathophysiology is that antibodies block, alter, or destroy the receptors for acetylcholine at the neuromuscular junction.
• Communication between the nerve and muscle is interrupted.
• Muscle contraction is prevented causing skeletal muscle weakness and fatigability.

Clinical Manifestations

• Subjective symptoms of Myasthenia Gravis include extreme muscle weakness, fatigue, dysphagia, diplopia caused by weakening of extraocular muscles, dysarthria, and dyspnea.
• Objective signs include ptosis, dysphonia, strabismus, mask-like facial expression, myasthenic snarling smile, drooling, and decreasing vital capacity leading to respiratory failure.

Diagnostic Tests

• The Tensilon test uses edrophonium chloride, a fast-acting AChE inhibitor, administered IV to diagnose MG.
• A positive Tensilon test shows immediate improvement in muscle strength after administration.
• The ice pack test involves applying ice to the eyes for 1-2 minutes to view any improvement in lid strength.
• An MRI is performed to check the thymus gland.
• Additionally an EMG can show delayed or failed nerve transmission.

Medical Management

• The goals of treatment are improving function, reducing, and removing circulating antibodies.
• There is no cure, so treatment does not stop the production of ACh receptor antibodies.

Pharmacological Management

• Pyridostigmine Bromide (Mestinon) is an anticholinesterase medication providing symptomatic relief.
• Adverse effects of Pyridostigmine Bromide include fasciculations, abdominal pain, diarrhea, and increased oropharyngeal secretions.
• Immunosuppressive drugs are given to reduce the production of the antibody such as corticosteroids, which require CBC monitoring, and Azathioprine (Imuran).
• Intravenous immune globulin is used to treat exacerbations and as a long-term adjunctive therapy.
• Plasmapheresis is a technique used to treat exacerbations.
• During plasmapheresis, the patient's plasma and plasma components are removed through a centrally placed large-bore double-lumen catheter.
• Next the blood cells and antibody-containing plasma are separated, after which the cells and a plasma substitute are reinfused.
• Surgical management includes a thymectomy, with the surgical removal of the thymus gland.
• It may take up to 3 years for the patient to benefit from the procedure due to the long life of circulating T cells.

Nursing Management

• Medication should be administered 30 minutes before meals.
• Medications to avoid include Barbiturates, Muscle relaxants, Morphine Sulfate, Neomycin, and Tranquilizers.
• Energy conservation suggests identifying the best times for rest.
• Minimize the risk of aspiration by timing mealtimes to coincide with the peak effects of anticholinesterase medications.
• It is best to rest before meals and sit upright during meals.
• Soft foods with gravy and sauce are encouraged.
• Suction should be available at home and supplemental feedings offered.
• For ocular manifestations, tape the eyes closed for short intervals and instill artificial tears regularly.

Complications

• Complications include respiratory failure, impaired communication, corneal ulceration, myasthenic crisis, and cholinergic crisis.

Myasthenic Crisis

• Myasthenic Crisis involves an acute exacerbation of MG.
• This is usually caused by rapid, unrecognized progression of the disease, inadequate medication, infection, fatigue, or stress.
• Symptoms include respiratory distress, varying degrees of dysphagia, dysarthria, eyelid ptosis, diplopia, and prominent muscle weakness.
• Management involves placing the patient in the ICU.
• ET intubation and mechanical ventilation help to secure the airway.
• Provide ventilator assistance and ongoing assessment for respiratory failure.
• Chest physical therapy alongside monitoring ABG, serum electrolytes, and input and output are key interventions.
• NGT feeding is utilized.
• Avoid sedative and tranquilizers.

Cholinergic Crisis

• Cholinergic Crisis results in depolarization of motor end plates.
• This crisis is often caused by overmedication with anticholinesterase.
• Clinical Manifestations include nausea and vomiting, diarrhea and abdominal cramps, pallor, facial muscle twitching, and hypotension.
• Interventions involve holding anticholinesterase medication and preparing to administer an antidote.
• ET intubation and mechanical ventilation may be required.