Remission Rates Better Short-term Than Long-term After Thymectomy

Rates of long-term disease remission after thymectomy — thymus removal surgery — among people with myasthenia gravis (MG) are lower than rates of remission over the first year after the procedure, according to a real-world study.

Most clinical factors, such as disease type, age, or sex were unrelated to the clinical response to thymectomy, the study found. Instead, a decline after surgery in levels of acetylcholine receptor antibodies — the most common type of self-reactive antibodies seen in MG patients — was associated with an increased likelihood of disease remission in the first year.

The study, “Short-term and sustained clinical response following thymectomy in patients with myasthenia gravis,” was published in the European Journal of Neurology. 

MG is an autoimmune disease in which autoantibodies attack the neuromuscular junction, which is the site where nerves and muscles communicate.

Although the exact source of these autoantibodies remains poorly understood, the thymus — an organ that is part of the body’s immune system — is thought to be involved in their production.

A thymectomy is sometimes performed as a treatment for MG. In particular, the procedure is often used for people with thymoma-associated MG, or MG associated with a thymus tumor. Evidence also suggests the procedure is effective in non-thymomatous cases, or those not associated with a tumor.

To learn more about remission rates, a research team in Austria retrospectively reviewed real-world outcomes after thymectomy in 94 MG patients who underwent surgery at the Medical University of Vienna over the last 30 years. Among the patients were 36 males and 58 females.

Of them, 68% had non-thymomatous MG — 54% with early-onset disease and 14% with late-onset MG. The remaining 32% of the patients had thymoma-associated MG. Time from disease onset to thymectomy lasted a median of 8.5 months.

An analysis of the removed thymus tissue from those with non-thymomatous MG revealed normal thymus tissue in 28 people and evidence of thymus gland enlargement in 36 patients. As expected, those with thymoma-associated MG all showed signs of thymoma at various stages, according to World Health Organization classifications.

Overall, disease remission for at least one year was achieved in 72% of patients. Age, sex, MG type, and previous treatment with steroids all were unrelated to the likelihood of a good clinical response to surgery, the study found. Additionally, there was no association between a good clinical response and findings in the thymus tissue analyses or in time to surgery after disease onset.

However, among those who sustained remission for a year, half (34 people) relapsed at a later time point. Such relapses occurred at a median of 89.5 months, or nearly 7.5 years after surgery. The data show that, in total, 34 people achieved sustained clinical remission.

The patients with sustained remission required less treatment with acetylcholinesterase inhibitors — a standard class of treatments for MG — or immunosuppressants after thymectomy.

MG patients often show elevated levels of antibodies against acetylcholine receptors, which are important for communication at the neuromuscular junction. Results showed that levels of these antibodies were not overall predictive of treatment response.

However, in a subset of patients who were not taking immunosuppressive treatments before surgery, greater declines in antibody levels from before surgery to after were significantly predictive of a greater likelihood of disease remission in the first year after the procedure.

This could highlight the potential of these antibodies as biomarkers of response to thymectomy, the researchers suggested.

Overall, the results show that early clinical responses to thymectomy are different from long-term ones, but relapses are not predicted by most pre-surgery clinical features.

“The fact that patients after thymectomy can suffer from relapses is perhaps not surprising given the fluctuating nature of the disease and also cautions against the use of the initial clinical response as the sole evaluation parameter after thymectomy,” the researchers wrote.

The occurrence of relapses after thymus removal could be due to the spread of the autoimmune response to other tissues outside the thymus, the researchers hypothesized, adding that this may mean further immunosuppressive treatments are still needed to suppress disease activity in some patients.