Universitas udayana

Faculty of medicine

Myasthenia gravis

Name:Gythrie KarthikasonNim:1102005209

Myasthenia gravisDefinitionMyasthenia gravis is a chronic autoimmune neuromuscular disease characterized by varying degrees of weakness of the skeletal muscles of the body. The hallmark of myasthenia gravis is muscle weakness that increases during periods of activity and improves after periods of rest. The muscles that control breathing and neck and limb movements may also be affected.

EpidemiologyFrequencyUnited StatesMyasthenia gravis is uncommon. Estimated annual incidence is 2 per 1,000,000.Mortality/MorbidityRecent advances in treatment and care of critically ill patients have resulted in marked decrease in the mortality rate. The rate is now 3-4%, with principal risk factors being age older than 40 years, short history of severe disease, and thymoma. Previously, the mortality rate was as high as 30-40%. SexThe female-to-male ratio is said classically to be 6:4, but as the population has aged, the incidence is now equal in males and females. AgeMyasthenia gravis presents at any age. Female incidence peaks in the third decade of life, whereas male incidence peaks in the sixth or seventh decade. Mean age of onset is 28 years in females and 42 years in males.

Causes and Risk Factors for Myasthenia Gravis MG usually is caused by a malfunction of the immune system. The causative factor is unknown, but the disorder may have a genetic link. Causes include a genetic defect, which results in congenital MG, and the circulation of maternal antibodies through the placenta, which result in transient neonatal MG. Acetylcholine (ACh) is a neurotransmitter that is involved in the transfer of information to muscle tissue. In myasthenia gravis, cells that bind to other cells to neutralize or destroy them (called antibodies) destroy acetylcholine receptor sites (AChR) in areas of muscle tissue that receive nerve impulses (called neuromuscular junctions), preventing nerve impulses from reaching the muscles. This results in weakness and rapid fatigue in affected muscles.

Pathophysiology of myasthenia gravis.Myasthenia gravis (MG) is arguably the best understood autoimmune disease, and its study has also led to fundamental appreciation of mechanisms of neuromuscular transmission. MG is caused by antibodies against the acetylcholine receptor (AChR), which produce a compromise in the end-plate potential, reducing the safety factor for effective synaptic transmission. It is clear that AChR antibody destruction of the postsynaptic surface is dependent on complement activation. A muscle-specific kinase has been recently found to be an antigenic target in MG patients without antibodies against the AChR. Autoantibody production in MG is a T-cell-dependent process, but how a breakdown in tolerance occurs is not known. In MG there is an interesting differential involvement of muscle groups, in particular, the extraocular muscles. This article reviews normal neuromuscular transmission, mechanisms of the autoimmune process of MG, and differential susceptibility of eye muscles to MG.

Symptoms Onset of the disorder may be sudden Affect any voluntary muscle The facial expression and swallowing are most frequently affected Weakness of muscles that control eye and eyelid movement causing blurred or double vision (diplopia) Difficulty in swallowing and slurred speech may be the first signs Drooping of one or both eyelids (ptosis), Unstable or waddling gait, weakness in arms, hands, fingers, legs, and neck, Shortness of breath Impaired speech (dysarthria).

DiagnosisMG can be a difficult diagnosis, as the symptoms can be subtle and hard to distinguish from both normal variants and other neurological disorders. A thorough physical examination can reveal easy fatigability, with the weakness improving after rest and worsening again on repeat of the exertion testing. Applying ice to weak muscle groups characteristically leads to improvement in strength of those muscles. Additional tests are often performed, as mentioned below. Furthermore, a good response to medication can also be considered a sign of autoimmune pathology.

TreatmentAnticholinesterase agents such as neostigmine and pyridostigmine, which help improve neuromuscular transmission and increase muscle strength.mmunosuppressive drugs such as prednisone, cyclosporine, and azathioprine which help improve muscle strength by suppressing the production of abnormal antibodies.ThymectomyPlasmapheresis a procedure in which abnormal antibodies are removed from the blood, and high-dose intravenous immune globulin, which temporarily modifies the immune system and provides the body with normal antibodies from donated blood.