Myasthenia gravis overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Myasthenia gravis (literally "serious muscle-weakness"; from Greek μύς "muscle", Template:Polytonic "weakness", and Latin gravis "serious"; abbreviated MG) is a neuromuscular disease leading to fluctuating muscle weakness and fatiguability. It is an autoimmune disorder, in which weakness is caused by circulating antibodies that block acetylcholine receptors at the post-synaptic neuromuscular junction,[1] inhibiting the stimulative effect of the neurotransmitter acetylcholine. Myasthenia is treated medically with cholinesterase inhibitors or immunosuppressants and in selected cases with thymectomy. At 200-400 cases per million it is one of the less common autoimmune disorders.[1]
Historical Perspective
The first possible patient with Myasthenia gravis, Openchancanough was first described by Virginian Chroniclers in 1664. His symptoms included fatigue, heavy eyelids and weak muscle tone. In the late 1800s the name Myasthenia gravis was created and the classic symptoms of the disease were described. The autoimmune nature of this disease was first described by Simpson and Nastuck in 1959-1960. The first important step in treatment of MG occurred in 1934 by Marry Walker. She observed that the symptoms of patients with myasthenia gravis in similar to those with curare poisoning so their symptoms can improve by a cholinesterase inhibitor like physostigmine. In 1937 Blalock described an improvement in his patient after removal of the thymus and established thymectomy as one of the treatment options of MG. In 1970s the use of immunosuppressants, azathioprine and plasma exchange became more prevalent.
Classification
Myasthenia gravis may be classified into 4 sub types based on presence of autoantibodies: Pure ocular form, generalized form with anti-AChR antibodies, the forms without classical anti-AChR antibodies, neonatal MG, congenital.
Pathophysiology
Myasthenia gravis is a neuromuscular disease caused by an autoimmune reactions. The main problem in this disease is the abnormal transmission of nerve impulses to muscle fibers in NMJ. Genes involved in the pathogenesis of Myasthenia gravis include: The Major Histocompatibility Complex, the CHRNA1 Locus, the PTPN22 Gene, the FCGR2 Locus and the CTLA4 Locus.
Causes
Myasthenia gravis may be caused by thymus abnormalities, genetic and environment.
Differentiating Myasthenia Gravis from other Diseases
Differential diagnosis for Myasthenia gravis includes: Adult Botulism, infant Botulism, guillian-Barre syndrome, eaton lambert syndrome, electrolyte disturbance, organophosphate poisoning, tick paralysis, tetrodotoxin poisoning, stroke, poliomyelitis, transverse myelitis, neurosyphilis, muscular dystrophy, multiple sclerosis, amyotrophic lateral sclerosisand myositis.