What is it?
In Greek, myasthenia means muscle weakness, and in Latin gravis means serious. Thus, myasthenia gravis is a potentially deadly disease that weakens muscles. Furthermore, myasthenia gravis is a long-term neuromuscular autoimmune disease that causes skeletal muscle weakness, and is categorized as a type 2 hypersensitivity, which causes cytotoxic injury.
People with myasthenia gravis might wake up feeling fine, but get progressively weaker as the day goes on, especially from repetitive movements.
To understand how myasthenia gravis occurs, a knowledge of muscular contraction is needed at the cellular level. Motor neurons release the neurotransmitter acetylcholine, which binds to nicotinic acetylcholine receptors on the muscle cell membrane. The binding of acetylcholine to its receptor a chain reaction that results in muscle contraction.
In myasthenia gravis, B-cells inappropriately make antibodies that bind to nicotinic acetylcholine receptors on the muscle cells. Once the antibodies bind to the receptors, the acetylcholine can no longer bind to its receptor. Therefore, the receptors don’t respond to the contract signal from the central nervous system.
Anti acetylcholine receptor antibodies can also activate the classical complement pathway that causes inflammation and destruction of the muscle cells and reduces the amount of acetylcholine receptors on the surface.
The most common effect of myasthenia gravis, occurring in about two thirds of patients, is related to the muscles around the eye, particularly ptosis and diplopia. Other common effects include dysphagia, slurred, soft or slow speech. The lethality of myasthenia gravis comes from the possibility of the inability to control the muscles responsible for breathing, meaning the patient cannot breathe without mechanical ventilation.
A male suffering from ptosis, a common effect of Myasthenia gravis
Classical complement pathway – a sequence of successive activation reactions involving enzymes from an initial stimulus that fights off bacterial infection
Cytotoxic – toxic to living cells
Diplopia – double vision, usually the result of impaired function of the extraocular muscles
Dysphagia – weakness of the muscles involved in swallowing, resulting in food being left over in the mouth after an attempt to swallow
Mediastinum - the mediastinum is the central compartment of the chest cavity between the two lungs
Motor neuron – neuron whose cell body is in the spinal cord and whose axon projects outwards, usually to control muscles
MRI – Magnetic resonance imaging, MRI, is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body
Ptosis – drooping or falling of the upper eyelid
Thymoma - a tumor arising from thymus tissue, found in 20% of patients with myasthenia gravis
Tomography – a technique for displaying a representation of a cross section through a human body or other solid object...