Thymectomy Raises Autoimmune Risk in Some MG Patients
Rheumatoid arthritis more likely in women, young people after removal of thymoma
The risk of developing another autoimmune disease, especially rheumatoid arthritis, increased in people with myasthenia gravis (MG) after surgery to remove a thymoma, or a tumor of the thymus gland, according to a recent Chinese study. Women and younger patients were at particularly higher risk.
The study, “Clinical characteristics of myasthenia gravis (MG) patients developing other autoimmune diseases after thymectomy from one single center cohort,” was published in Thoracic Cancer.
MG is an autoimmune disease caused by self-reactive antibodies targeting and attacking proteins of neuromuscular junctions, the sites of communication between nerve and muscle cells.
The disease is often linked to thymus abnormalities such as thymomas. A thymectomy, or surgical removal of the thymus, is often a treatment of choice to manage MG. The thymus gland is an organ in the chest and is part of the immune system.
Prior studies have reported the onset of autoimmune diseases such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) in MG patients, particularly after a thymectomy.
“The removal of the thymus gland may have a significant impact on the immune function of the body, and further break the balance of the immune system,” the researchers wrote.
Raised risk of autoimmune disorder with thymectomy?
But whether a thymectomy increases the risk for additional autoimmune diseases in MG required more evidence, which led a team led by researchers in China to assess the incidence of autoimmune diseases in a large group of MG patients who had a thymectomy at the Beijing Hospital from January 2012 to August 2021.
After excluding patients with incomplete records and a short follow-up, 445 patients — 228 men and 217 women, with a mean age of 47 at the time of surgery — were included in the study.
All the surgeries were performed using video-assisted thoracoscopic surgery (VATS) or sternotomy with follow-up happening every six months in the two years after surgery and once a year thereafter. Patients were followed for a median of 72 months (six years).
A thymoma was found in 132 patients (29.7%) and 47 (10.6%) had a myasthenic crisis within the first month after a thymectomy. The 10-year overall survival after the surgery was 94.2%.
The overall effective rate of the surgery was 85.6% and 63 MG patients had concomitant autoimmune diseases, a frequency of 14.2%. This is greater than the incidence rate previously reported in a Chinese MG group (11.6%).
Forty seven patients (10.6%) were diagnosed with other autoimmune diseases before having a thymectomy. Hyperthyroidism (overactive thyroid) was the most common disorder (40.4%) followed by Hashimoto’s thyroiditis (27.7%), another autoimmune disorder of the thyroid gland.
Patients with additional autoimmune diseases included more women and a lower proportion of those with thymomas.
After surgery and a median follow-up of 48 months, 19 patients (4.3%) developed a single, new autoimmune disease, a higher incidence than previously reported for such patients in a Taiwanese study (3.3%).
The most frequent type of new onset autoimmune disease following thymectomy was Hashimoto’s thyroiditis (47.4%) and RA (31.6%), which differ from those most commonly seen before thymectomy.
Patients who went on to develop a new autoimmune disease after surgery were more frequently women and younger at the time of disease onset than those who didn’t. No significant differences were found in other clinical characteristics and postoperative MG treatment.
All six patients who developed RA after thymectomy were women, and only one was over 50 at surgery. One had a thymoma and five had thymic hyperplasia, or thymus enlargement.
“We observed a higher incidence rate of autoimmune diseases, especially rheumatoid arthritis, in MG patients after thymectomy,” the researchers wrote. “New onset ADs [autoimmune diseases] tended to occur in female and young nonthymoma MG patients. The postoperative effect of MG was not related with the new occurrence of ADs.”