Removal of Thymus Better Than Medications for Treating MG Patients Without Thymoma, Review Shows

Surgical removal of the thymus to treat myasthenia gravis (MG) patients without a thymoma — a tumor in the thymus — seems to be more effective than medications, according to a new review study from Brazil.

The study, “Thymectomy in nonthymomatous myasthenia gravis — systematic review and meta-analysis,” appeared in the Orphanet Journal of Rare Diseases.

Abnormal function of the thymus and impaired immune regulation are seen in MG patients with antibodies targeting acetylcholine receptors at the neuromuscular junction — the site where nerves and muscle cells communicate.

The thymus is a small organ in the upper chest that makes lympocytes, a type of white blood cell, that protect people against infection.

Medications for myasthenia gravis intend to either improve transmission of nerve signals to muscles or alter or suppress the immune response. Thymectomy, a surgical procedure to remove the thymus, is another method to treat MG, and has long been used to stop the production of autoantibodies.

A thymectomy is a common strategy in about 15 percent of MG patients who develop a thymoma, but support for its use in patients who don’t develop these tumors (non-thymomatous MG) is still lacking.

The 2016 guidelines of the American Academy of Neurology for the management of myasthenia gravis recommended thymectomy in non-thymomatous MG patients as an option to avoid or lower the dose or duration of immunotherapy or in cases of no response or intolerable side effects with these medications.

In the same year, results of a clinical trial (NCT00294658) showed that thymectomy improved the symptoms in patients with non-thymomatous MG over three years.

The research team conducted a systematic review of the literature to evaluate the effectiveness of thymectomy in non-thymomatous MG, compared to medical treatment. Specifically, the investigators assessed remission and improvement rates with either approach.

The review included 19 studies with at least 10 adults in each group. Articles published before 1970 and those describing patients treated before 1950 were excluded.

A total of 5,841 patients — 2,911 surgical and 2,930 nonsurgical — were analyzed. Two randomized clinical trials and four retrospective studies showed that thymectomy was superior to treatment with medications.

In a meta-analysis — a type of statistical study that combines the results of various studies — of 17 studies (5,686 patients), remission was greater in patients who underwent surgery.

Of 13 other studies assessing improvement rates, six reported that surgery outperformed medical treatment. However, they showed high variability, which warrants caution when analyzing the greater remission with thymectomy, the authors noted.

Overall, “thymectomy may be considered effective in the treatment for non-thymomatous MG, with remission rate higher than for non-surgical treatment,” the researchers wrote.

Among the study’s limitations, the scientists mentioned that it was not possible to conduct subgroup analyses by type of thymectomy, gender, and age.

“At the moment we need studies that show which subgroups would most benefit from the treatment,” they said.