Myasthenia gravis
Autoimmune disease resulting in skeletal muscle weakness / From Wikipedia, the free encyclopedia
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Myasthenia gravis (MG) is a long-term neuromuscular junction disease that leads to varying degrees of skeletal muscle weakness.[1] The most commonly affected muscles are those of the eyes, face, and swallowing.[1][5] It can result in double vision, drooping eyelids, and difficulties in talking and walking.[1] Onset can be sudden.[1] Those affected often have a large thymus or develop a thymoma.[1]
Myasthenia gravis | |
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Eye deviation and a drooping eyelid in a person with myasthenia gravis trying to open her eyes | |
Specialty | Neurology |
Symptoms | Varying degrees muscle weakness, double vision, drooping eyelids, trouble talking, trouble walking[1] |
Usual onset | Women under 40, men over 60[1] |
Duration | Long term[1] |
Causes | Autoimmune disease[1] |
Diagnostic method | Blood tests for specific antibodies, edrophonium test, nerve conduction studies[1] |
Differential diagnosis | Guillain–Barré syndrome, botulism, organophosphate poisoning, brainstem stroke,[2] metabolic myopathies |
Treatment | Medications, surgical removal of the thymus, plasmapheresis[1] |
Medication | Acetylcholinesterase inhibitors (neostigmine, pyridostigmine), immunosuppressants[1] |
Frequency | 50 to 200 per million[3][4] |
Myasthenia gravis is an autoimmune disease of the neuromuscular junction which results from antibodies that block or destroy nicotinic acetylcholine receptors (AChR) at the junction between the nerve and muscle.[6][7][1] This prevents nerve impulses from triggering muscle contractions.[1] Most cases are due to immunoglobulin G1 (IgG1) and IgG3 antibodies that attack AChR in the postsynaptic membrane, causing complement-mediated damage and muscle weakness.[8] Rarely, an inherited genetic defect in the neuromuscular junction results in a similar condition known as congenital myasthenia.[9][10] Babies of mothers with myasthenia may have symptoms during their first few months of life, known as neonatal myasthenia.[1] Diagnosis can be supported by blood tests for specific antibodies, the edrophonium test, electromyography (EMG), or a nerve conduction study.[1]
MG is generally treated with medications known as acetylcholinesterase inhibitors, such as neostigmine and pyridostigmine.[1] Immunosuppressants, such as prednisone or azathioprine, may also be used.[1] The surgical removal of the thymus may improve symptoms in certain cases.[1] Plasmapheresis and high-dose intravenous immunoglobulin may be used during sudden flares of the condition.[1] If the breathing muscles become significantly weak, mechanical ventilation may be required.[1] Once intubated acetylcholinesterase inhibitors may be temporarily held to reduce airway secretions.[11]
MG affects 50 to 200 people per million.[3][4] It is newly diagnosed in 3 to 30 people per million each year.[12] Diagnosis has become more common due to increased awareness.[12] MG most commonly occurs in women under the age of 40 and in men over the age of 60.[1][5][13] It is uncommon in children.[1] With treatment, most live to an average life expectancy.[1] The word is from the Greek mys, "muscle" and astheneia "weakness", and the Latin gravis, "serious".[14]