Thymectomy

Thymectomy is a surgical procedure in which the thymus gland, an immune organ, is removed. This surgery can be performed by different techniques that can be more or less invasive. It is one of the main treatment methods for myasthenia gravis (MG).

How does thymectomy work?

The thymus is a small gland in the upper chest, under the breastbone. It is an important part of the immune system’s development in children, but becomes redundant around puberty. As many as 15% of MG patients have a tumor in the thymus, called a thymoma, and another 60–75% have abnormal enlargement of this gland.

MG is driven by self-targeting antibodies, or autoantibodies, that interfere with the communication between nerve and muscle cells. Removing the thymus is thought to reduce the production of these autoantibodies, possibly by lessening the activity of certain immune cells. However, the exact mechanism(s) by which thymectomy benefits MG patients remains incompletely understood.

Thymectomy is a long-term treatment that does not result in an immediate change in symptoms. As such, patients will continue taking MG-related medications after surgery, with the goal of eventually reducing the dosage or stopping treatment altogether, depending on the individual’s symptoms.

The benefits derived from thymectomy vary substantially from patient to patient. In some individuals, symptoms may disappear permanently, whereas others may experience minimal changes in symptoms after surgery. According to the Cleveland Clinic, about 70% of patients experience a significant reduction in medication needs or go fully into remission within a year of undergoing the procedure.

Thymectomy in clinical research

A likely connection between the thymus gland and MG was first noted in the early 1900s, when surgeons observed that removing a thymoma could substantially ease a patient’s MG symptoms. Since then, similar responses have been noted in patients who do not have a thymoma.

A Phase 3 trial (NCT00294658), sponsored by the University of Alabama at Birmingham, enrolled 126 adults with MG who did not have a thymoma. All participants were treated with prednisone (an immune-suppressing steroid), and some also underwent thymectomy.

Results showed that, after three years, patients who received thymectomy reported significantly less severe disease, as measured by the Quantitative Myasthenia Gravis (QMG) score. Thymectomy-treated participants also experienced fewer hospitalizations and required fewer additional immune-suppressing medicines. Additional data on a subset of participants showed similar results after five years.

Other details

In general, this type of surgery is recommended for patients with thymomas or those under age 60 who have mild to moderate MG symptoms. It is usually not used to treat patients with ocular MG, in whom the disease is limited to muscles controlling eye and eyelid movements.

As with any surgical procedure, thymectomy involves risks, especially for individuals whose MG makes it harder for them to breathe. Nonetheless, with modern advances in surgical techniques, the procedure is generally considered safe, with mortality rates of 1% or less even for people with poorly controlled MG.

Common complications related to thymectomy include infections, myasthenic crisis, and injury to the nerves in the throat.

Thymectomy should be avoided in patients who cannot safely undergo surgery, such as those who cannot tolerate general anesthesia or those with uncontrolled bleeding problems.

Last updated: Jan 21, 2022, by Marisa Wexler, MS

 


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