Myasthenia gravis

Myasthenia gravis
DiplopiaMG1.jpg
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]
Similar conditions Guillain-Barre syndrome, botulism, organophosphate poisoning, brainstem stroke [2]
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 (MG) is a long-term neuromuscular 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] It can result in double vision, drooping eyelids, trouble talking, and trouble walking. [1] Onset can be sudden. [1] Those affected often have a large thymus gland or develop a thymoma. [1]

Myasthenia gravis is an autoimmune disease which results from antibodies that block or destroy nicotinic acetylcholine receptors at the junction between the nerve and muscle. [1] This prevents nerve impulses from triggering muscle contractions. [1] Rarely, an inherited genetic defect in the neuromuscular junction results in a similar condition known as congenital myasthenia. [5] [6] 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, or a nerve conduction study. [1]

Myasthenia gravis 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 gland 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]

MG affects 50 to 200 per million people. [4] [3] It is newly diagnosed in three to 30 per million people each year. [7] Diagnosis is becoming more common due to increased awareness. [7] It most commonly occurs in women under the age of 40 and in men over the age of 60. [1] It is uncommon in children. [1] With treatment, most of those affected lead relatively normal lives and have a normal life expectancy. [1] The word is from the Greek mys "muscle" and astheneia "weakness", and the Latin: gravis "serious". [8]

Video explanation

Signs and symptoms

The initial, main symptom in MG is painless weakness of specific muscles, not fatigue. [9] The muscle weakness becomes progressively worse during periods of physical activity and improves after periods of rest. Typically, the weakness and fatigue are worse toward the end of the day. [10] MG generally starts with ocular (eye) weakness; it might then progress to a more severe generalized form, characterized by weakness in the extremities or in muscles that govern basic life functions. [11]

Eyes

In about two-thirds of individuals, the initial symptom of MG is related to the muscles around the eye. [9] There may be eyelid drooping ( ptosis due to weakness of levator palpebrae superioris) [12] and double vision ( diplopia, [9] due to weakness of the extraocular muscles). [10] Eye symptoms tend to get worse when watching television, reading, or driving, particularly in bright conditions. [9] Consequently, some affected individuals choose to wear sunglasses. [9] The term "ocular myasthenia gravis" describes a subtype of MG where muscle weakness is confined to the eyes, i.e. extraocular muscles, levator palpebrae superioris, and orbicularis oculi. [12] Typically, this subtype evolves into generalized MG, usually after a few years. [12]

Eating

The weakness of the muscles involved in swallowing may lead to swallowing difficulty ( dysphagia). Typically, this means that some food may be left in the mouth after an attempt to swallow, [13] or food and liquids may regurgitate into the nose rather than go down the throat ( velopharyngeal insufficiency). [10] Weakness of the muscles that move the jaw ( muscles of mastication) may cause difficulty chewing. In individuals with MG, chewing tends to become more tiring when chewing tough, fibrous foods. [9] Difficulty in swallowing, chewing, and speaking is the first symptom in about one-sixth of individuals. [9]

Speaking

Weakness of the muscles involved in speaking may lead to dysarthria and hypophonia. [9] Speech may be slow and slurred, [14] or have a nasal quality. [10] In some cases, a singing hobby or profession must be abandoned. [13]

Head and neck

Due to weakness of the muscles of facial expression and muscles of mastication, facial weakness may manifest as the inability to hold the mouth closed [9] (the "hanging jaw sign") and as a snarling expression when attempting to smile. [10] With drooping eyelids, facial weakness may make the individual appear sleepy or sad. [9] Difficulty in holding the head upright may occur. [14]

Other

The muscles that control breathing ( dyspnea) and limb movements can also be affected; rarely do these present as the first symptoms of MG, but develop over months to years. [15] In a myasthenic crisis, a paralysis of the respiratory muscles occurs, necessitating assisted ventilation to sustain life. [16] Crises may be triggered by various biological stressors such as infection, fever, an adverse reaction to medication, or emotional stress. [16]

Other Languages
العربية: وهن عضلي وبيل
azərbaycanca: Miasteniya
français: Myasthénie
Bahasa Indonesia: Miastenia gravis
ქართული: მიასთენია
қазақша: Миастения
Кыргызча: Миастения
മലയാളം: മൈസ്തീനിയ
Nederlands: Myasthenia gravis
oʻzbekcha/ўзбекча: Miasteniya
Piemontèis: Miastenìa greva
polski: Miastenia
português: Miastenia grave
русский: Миастения
Simple English: Myasthenia gravis
slovenčina: Ťažká myasténia
slovenščina: Miastenija gravis
српски / srpski: Miastenija gravis
татарча/tatarça: Миастения
українська: Міастенія
Tiếng Việt: Bệnh nhược cơ