In myasthenia gravis, the body's antibodies jam the switch between nerve and muscle
Imagine eyelids that droop by evening and a smile that turns into a snarl. In myasthenia gravis the immune system blocks the receptors that let nerves tell muscles to contract, so strength drains with use and returns with rest. Its Greek and Latin name means, bluntly, serious muscle weakness.
Nerves signal muscles by releasing acetylcholine, which docks on receptors at the neuromuscular junction. In most patients, antibodies of the IgG1 and IgG3 types attack those receptors and trigger complement, a part of the immune system that damages the membrane, so impulses no longer spark a contraction. Some patients have an enlarged thymus, and a few have a thymus tumour.
The hallmark is painless weakness that worsens with activity and eases after rest, typically at its worst late in the day. About two-thirds of people notice it first around the eyes: a drooping lid or double vision, made worse by reading, television or driving in bright light, which is why some wear sunglasses. It can spread to the face, jaw and throat, leaving food in the mouth after swallowing, liquids escaping through the nose, speech that turns slurred or nasal, a jaw that hangs open, or a head that is hard to hold up. Some singers have had to give up singing. In a myasthenic crisis the breathing muscles fail and a ventilator is needed; infection, fever, stress or a drug reaction can set one off.
Many common medicines can unmask or aggravate the disease, including certain antibiotics such as azithromycin and ciprofloxacin, some cancer immunotherapies and beta blockers. In one 2019 review of 169 people whose condition appeared or worsened on statins, 138 developed the generalised form.
Between 50 and 200 people per million live with it, and 3 to 30 per million are newly diagnosed each year, more often as awareness grows. It mostly strikes women under 40 and men over 60 and is uncommon in children. Drugs such as pyridostigmine ease symptoms by slowing acetylcholine breakdown, but nearly everyone also needs immune-suppressing medicine such as prednisone, and removing the thymus helps some. With treatment, most people lead full lives of normal length.
Source: Myasthenia gravis
