Myasthenia gravis (MG) is a neuromuscular disease in which the immune system produces abnormal antibodies that destroy muscle receptors for acetylcholine, a neurochemical that activates the muscles and causes contractions. Antibodies also can target molecules that enable acetylcholine receptors to work properly. Damage to the part of the muscle that reacts to chemical signals from nerves impairs its ability to contract, causing muscle weakness that affects the ability to swallow and move limbs and eyes. Other symptoms include double or blurred vision, droopy eyelids, and trouble speaking.
The thymus gland—located beneath the breastbone—is thought to be associated with MG as it may trigger and control the immune cells that regulate production of the antibodies that damage acetylcholine receptors or molecules that enable the receptors to work properly. About 10 to 15 percent of people with MG also have tumors on their thymus glands, called thymomas, which are usually benign. (A CT scan to detect thymomas is part of the medical evaluation for people with MG.) Almost 100 years, ago surgeons discovered that removing thymomas in people with the disease improved their symptoms. Researchers subsequently discovered that removing the gland itself improved symptoms in people with MG who didn't have thymomas.
Today, the procedure, called a thymectomy, is one of the ways to treat MG. Other therapies include drugs, such as the steroid prednisone, that suppress antibody production or improve nerve signal transmission; plasmapheresis, which removes antibodies from the blood; and high-dose intravenous immunoglobulin, which delivers healthy antibodies from donated blood to temporarily fortify the immune system. Neurologists typically start patients on drugs even if a thymectomy is being considered since it can take a year or more for a thymectomy to be fully effective and not everyone achieves remission.
A study in the New England Journal of Medicine in 2016 compared the results of a thymectomy plus prednisone versus prednisone alone in 126 people ages 18 to 65 who had generalized MG without thymomas and found that the thymectomy-prednisone combination resulted in improved symptoms, fewer hospitalizations, and a reduced dose of steroids for many participants.
The effectiveness of a thymectomy in reducing or eliminating symptoms depends on age, duration, and severity of the disease. Remission can be as high as 70 percent a year after surgery. The operation is not usually recommended for people older than 60, who have types other than generalized MG associated with acetylcholine receptor antibodies, or whose weakness is limited to the eye muscles.
A thymectomy can be performed via open-chest surgery—which involves cutting the breastbone down the middle and opening the entire chest cavity to remove the gland—and robotic surgery, in which surgeons make small incisions and insert tiny robotic tools that they manipulate by looking at a video monitor. A 2019 study in the Annals of Cardiothoracic Surgery found that robotic thymectomy resulted in less blood loss, fewer post-surgery complications, a shorter hospital stay, and more thymus tissue removed than open-chest surgery. During the procedure, the entire gland is removed, as is surrounding fat, which may contain small amounts of thymus.
Patients usually spend a few days to a week in the hospital while they recover. Returning to pre-surgery activities such as driving and lifting heavy objects will depend on the type of surgery, overall health, and rate of recovery. Patients usually continue any medications they had before surgery. During follow-up appointments, doctors can determine if and how to taper dosages.
For many patients, symptoms begin to improve within a year of the surgery, and some go into remission permanently and no longer experience weakness or take medication.
Thymectomies are generally covered by insurance, but patients may need to document the type of surgery and reason for it. In addition, some insurers only cover the procedure if the surgeon is in their network.
Dr. Ruff is professor emeritus of neurology and neuroscience at Case Western Reserve University School of Medicine in Cleveland.
