# Myasthenia Gravis --- **Myasthenia gravis** is an [[autoimmune disorder]] that targets the communications between the [[nerves]] and [[skeletal muscle]], which results in various degrees of weakness in the skeletal muscles. This can be very debilitating. There are different kinds of MG, but generally speaking the immune system produces [[antibodies]] that target (i.e. destroy or block) the receptor sites for [[acetylcholine]] or a muscle's [[enzyme-linked receptors|tyrosine kinase receptor]]. ## Risk Factors - in AFAB people it's most common between ages 20-30 - in AMAB people it's more common after age 50 ## Signs & Symptoms Myasthenia gravis particularly effects the muscles that control the eyes, mouth, throat and limbs, though it can even involve difficulty in chewing/swallowing or breathing or pronouncing words. - Ptosis of eyelids, and diplopia (double vision) - This is because the brain uses muscles to finely control the alignment of the eyes, and the weakness in those muscles can cause them to come out of alignment, which is what causes double vision. - The **ice pack test** can be used to determine if the ptosis is due to MG. If an eye pack is placed on the eyelid for a minute, and the ptosis improves, this is a positive indication of MG - this is because the cold decreases the activity of acetylcholinesterase, increasing the availability of Ach - muscle weakness that worsens as muscles are used. Facial muscle causes mask-like appearance; smile can appear like a snarl. - dysphonia/dysphagia ## Complications A **myasthenic crisis** can occur if the [[diaphragm]] and chest muscles become affected, leading to shallow or ineffective [[pulmonary ventilation]]. It can even block the airway if the throat muscles weaken and secretions build up. The most common trigger for a myasthenic crisis is an increased demand. A respiratory infection is dangerous because it can lead to a myasthenia crisis. A **cholinergic crisis** is a rare but dangerous condition, usually occurring if there is an overmedication of anticholinesterases. This leads to an overactivation of the [[parasympathetic nervous system]] and results in respiratory failure that may require intubation. [[atropine]] can be given to treat this. ## Diagnostic Tests - **single-fiber electromyography** detects delays or a failure of neuromuscular transmission - 99% sensitive in confirming MG - the ice pack test (see above) - lab draw for acetylcholine antibodies - repetitive nerve stimulation - will see a decrease in successive action potentials in MG - the [[thymus]] may be enlarged as it's the site for acetylcholine receptor antibody production ## Treatment Medical: - **Acetylcholinesterase inhibitor drugs** work quickly by stopping the breakdown of [[acetylcholine]]. It does *not* prevent immune system from attacking the neuromuscular junction, but it *does* prevent the breakdown of acetylcholine, which keeps levels high and available to the muscles, which improves muscle strength. - Taking this before meals can help reduce the risk of aspiration. - patient education is important here - Taking this can help maintain the strength of the breathing muscles. - [[glucocorticoids|Glucocorticoids]] (i.e. corticosteroids) are generally used to reduce symptoms of [[autoimmune disorder]] (namely, [[inflammation]]). These work by surprising the immune system. Suppressed immune system means fewer antibodies to attack the healthy tissue, but also few antibodies to fight actual disease. Thus, it's usually only proscribed if the acetylcholinesterase inhibitors aren't fully working—however, most people do need to take both long term. - [[corticosteroids|Prednisone]] is the mostly commonly prescribed steroid for MG because it's relatively inexpensive and safe. Surgical: - Removal of the [[thymus]] - The thymus is thought to trigger or maintain the production of these [[acetylcholine]] antibodies. People with myasthenia gravis sometimes have enlarged thymuses, and removal of it can help symptoms/clear it up, though we're not sure *exactly* why. ## Nursing Considerations - medication management and education is crucial - educate on strategies to conserve energy - rest throughout the day - schedule activities for peak energy - risk for aspiration - avoid factors that exacerbate symptoms - emotional stress - infections (especially respiratory) - vigorous physical activity - high environmental temperature ___