Summary
Myasthenia Gravis is a chronic disorder of the neuromuscular apparatus. It is an autoimmune condition, where the body’s natural defence mechanism mistakes it’s own neuromuscular components as foreign invaders and attacks it, leading to their improper function. It mainly affects the muscles of the body which are in our control- the arms, legs, face, throat and diaphragm. It progresses gradually, and the main symptom is weakness/ fatigue of the muscles which is very often mistaken for generalised exhaustion and neglected. An early diagnosis and treatment will result in tremendous improvement.
Over the years, a number of treatment options have been tried and have been found to be incredibly helpful. Although newer drugs and treatments are still being hunted for.[1]
Keywords: Myasthenia Gravis, Neuromuscular, Autoimmune, Weakness
Introduction
Myasthenia Gravis is a fairly common condition. It occurs in 4.1 to 30 cases per million person-years, and it’s prevalence ranges from 150 to 200 cases per million. [1]
It is a neuromuscular disease that presents with the main complaint of easy fatigability and muscle weakness in the age groups of <40 years in women and >60 years in men. These symptoms are very similar to general exhaustion, as seen in the older age group and could get neglected until later, when the disease has progressed to cause significant damage to the muscles.
There is a variant of this disease that occurs in children, called Neonatal Myasthenia which is short lived and disappears in 2 to 3 months after birth. Sometimes, certain mutations or genetic abnormalities can cause Myasthenia Gravis, which is called Congenital MG. [2]
Why does MG occur?
Neuromuscular refers to the fact that there is a problem in the transmission of signals from the nerve to the muscle, leading to decreased or no muscle action. The nerves secrete chemical substances called “Neurotransmitters” which go and bind on certain receptors on the muscle. The main chemical for muscle contraction is Acetylcholine, and hence the receptors are called “Acetylcholine receptors or AchR”
In MG, the body produces Antibodies that block or destroy the receptors on the muscle, due to which Acetylcholine does not bind. This causes less muscle contraction or sometimes, no contraction.
Symptoms
Drooping of one or both eyelids
Blurred or double vision
Difficulty swallowing
Shortness of breath
Weakness in arms, hands, fingers, legs and neck
Rarely, MG. can be associated with the swelling of thymus (Thymoma), a small gland situated in the chest, responsible for making Antibodies in the body to fight infections. [2,3]
Diagnosis
A thorough physical and Neurological examination will show signs of weakness of eyelid muscles and other voluntary muscles, and no loss of sensation.
Blood tests: To check for presence of Acetylcholine receptor Antibodies (AchR) and Antibodies against muscle specific kinase (Anti MUSK antibodies). In some cases, these antibodies may be absent. Such a patient would be having “Seronegative MG”. Some minor antibodies are Anti-agrin and LRP4 antibodies.
Electrodiagnostic Tests: Repetitive Nerve Stimulation, Single Fiber Electromyography (SFEMG).
Ice pack test: Heat slows the signal transmission to muscle whereas cold temperature makes it faster. Keeping an ice pack on the drooping eyelid May sometimes show improvement due to the above mentioned reason and aids in diagnosing Myasthenia.
Edrophonium test. [2,3]
Treatment
Cholinesterase inhibitors: These drugs reduce the breakdown of Acetylcholine and hence increase the muscle contraction.
Corticosteroids
Non-steroidal immunosuppressive medications: Cyclosporine, Mycophenolate mofetil
Special drugs called Eculizumab, Ravulizumab and Rituximab suppress our immune attack on the receptors. Many new drugs in this category have been approved for the treatment of MG.
Plasmapheresis
Intravenous and subcutaneous immunoglobulins
Thymectomy: In 10% of individuals, thymus gland is enlarged with presence of Ach receptor Antibodies. [3]
Myasthenia Gravis and Pregnancy:
It is seen that MG does not affect pregnancy, except in the first trimester where it can cause a flare up of the disease. Although it is associated with increased risk of premature rupture of membranes and spontaneous abortions. Cholinesterase inhibitors and Corticosteroids are the drugs of choice in pregnancy. [4]
References:
Dresser L, Wlodarski R, Rezania K, Soliven B. Myasthenia Gravis: Epidemiology, Pathophysiology and Clinical Manifestations. J Clin Med. 2021 May 21;10(11):2235. doi: 10.3390/jcm10112235. PMID: 34064035; PMCID: PMC8196750.
Myasthenia Gravis https://www.ninds.nih.gov/health-information/disorders/myasthenia-gravis
Pascuzzi RM, Bodkin CL. Myasthenia Gravis and Lambert-Eaton Myasthenic Syndrome: New Developments in Diagnosis and Treatment. Neuropsychiatr Dis Treat. 2022 Dec 22;18:3001-3022. doi: 10.2147/NDT.S296714. PMID: 36578903; PMCID: PMC9792103.
Alfaro-Paredes K, Aguilar-Ydiáquez C, Aguirre-Flores R, Schulz-Cáceres H. Miastenia gravis y embarazo: impacto y abordaje [Myasthenia gravis and pregnancy: impact and approach]. Rev Neurol. 2022 Sep 1;75(5):117-122. Spanish. doi: 10.33588/rn.7505.2022207. PMID: 35880965; PMCID: PMC10280747.
Comments