• Myasthenia gravis is an acquired autoimmune disorder affecting transmission at neuromuscular junction. It is an autosomal dominant condition. 80-90% of patients will have auto antibodies to the acetylcholine receptors of the post synaptic membrane. Patients exhibit prolonged neuromuscular blockade to non-depolarizing muscle relaxants; but usually show some resistance to the muscle paralysis of succinylcholine. When MG is suspected the first test that may be performed is the Tensilon test using edrophonium 2mg IV wait 30 seconds for effect, assess for improvement in muscle strength that lasts for 5minutes. Repeated doses of 8mg may be given. If this test is positive supportive care is required until the neuromuscular blockade improves.
  • Myasthenia gravis is an autoimmune disorder that occurs 1/20,000 persons and is characterized by injury of the acetylcholine receptors at the postsynaptic neuromuscular junction. These patients exhibit marked sensitivity to nondepolarizing muscle relaxants and slight resistance to succinylcholine
  • Myasthenia gravis (MG) is a neuromuscular disease that is characterized by weakness and fatigability of skeletal muscles. The MG patient is more sensitive to the use of nondepolarizing relaxants. However, because there are fewer functional receptors the MG patient may demonstrate increased resistance to depolarizing muscular relaxants. While many anesthesiologists may prefer to avoid neuromuscular blocking agents, succinylcholine (in higher doses) can be used in the MG patient and provide satisfactory intubating conditions. Succinylcholine may precipitate hyperkalemia in muscular dystrophy, spinal cord injuries less than 6 to 8 months and MS.
  • Anticholinesterase therapy is the primary pharmacologic treatment of patients with MG. The goal of the administration of an anticholinesterase agent is to increase the amount of acetylcholine. The increase in acetylcholine overcomes the reduction in acetylcholine receptors with a resultant increase in neuromuscular function. The anticholinesterase agents generally used in the management of MG are edrophonium, pyridostigmine, neostigmine and ambedonium. These agents do not cross the blood brain barrier. Pyridostigmine is the most commonly prescribed agent because of its 3 – 6 hour duration and the fewer muscarinic side effects. Administration of excessive amounts of anticholinesterase agents can result in cholinergic crisis. Cholinergic crisis is manifested by bradycardia, hypotension, increased secretions, lacrimation, wheezing, muscle weakness, nausea and vomiting, and constricted pupils.
  • There are several points to consider in the anesthetic management of a patient with MG. (1) Respiratory function should be assessed preoperatively through pulmonary function tests. Opioids must be used sparingly to avoid further compromising a patient with diminished respiratory reserve. (2) There is differing opinions pertaining to the continuation of the patient’s anticholinesterase agent. If the patient continues their anticholinesterase there is the potential for various drug interactions including prolongation of the succinylcholine, and antagonism of the nondepolarizing neuromuscular blocking agent. Continuation of the anticholinesterase has the potential risk of resulting in cholinergic crisis. The benefit of stopping the anticholinesterase agent is the avoidance of a cholinergic crisis post-operatively. Additionally, the withholding of the anticholinesterase agent results in muscle weakness and a reduction or elimination of the need for neuromuscular blockade. If neuromuscular blockade is required the MG patient demonstrates a resistance to succinylcholine and a prolongation of its effects; and an increased sensitivity to nondepolarazing agents. The latter is a result of the diminished neuromuscular receptors in a patient with MG