What is
the lesion of myasthenia gravis (MG)?
MG is an autoimmune disease of the motor
endplate.
It presents with easy fatigability of voluntary
muscles followed by recovery with rest. Its first manifestation is frequently
diplopia. Often it is generalized and progressive. The incidence approximates
1:2,000 adults. MG is an antibody-mediated disorder. The amount of presynaptic
acetylcholine released is normal or increased. Antibodies are produced to the
acetylcholine receptor of the neuro-muscular junction. In 10–15% of patients
with MG, the presence of antibodies cannot be demonstrated. Antibodies are of
the immunoglobulin G (IgG) class and are specific for the α subunit of the endplate receptor. Myasthenics are noted to have
70–80% fewer receptors on the motor endplate and fewer folds in the synaptic
cleft. Reduction in the number of receptors is brought about by functional
block, increased rate of receptor degradation, or complement-mediated lysis of
the postsynaptic membrane. Under normal conditions, only 25–30% of receptors
are required for neuromuscular transmission. The decrease in receptors
represents a reduction in the margin of safety of neuromuscular transmission.
These patients are extremely sensitive to any agent that interferes with
neuromuscular transmission.
Related Topics
Privacy Policy, Terms and Conditions, DMCA Policy and Compliant
Copyright © 2018-2023 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.