Similar Clinical Characteristics With MG Onset Before or After Thymectomy, Study Shows

Patients who develop myasthenia gravis (MG) either before or after surgical removal of the thymus (thymectomy) due to a thymoma — a tumor originating from the thymus — share similar clinical characteristics, a study shows.

Moreover, testing for anti‐acetylcholine receptor (AChR) antibody levels, or electrophysiological tests in patients with thymoma who don’t have symptoms of the neuromuscular condition, may help predict the development of MG post-thymectomy.

The study, titled “Frequency and features of myasthenia gravis developing after thymectomy,” was published in the European Journal of Neurology.

MG is an autoimmune disease that is largely caused by autoantibodies against the acetylcholine receptors (AChR) on muscle tissue.

Abnormalities of the thymus, including thymoma, have been shown to play a role in the disease mechanisms in MG patients who have anti-AChR antibodies.

Thymectomy improves symptoms of people with myasthenia gravis who have AChR antibodies. It is an established treatment for those with MG and thymoma.

In clinical practice, physicians rarely encounter patients with thymoma who don’t display any symptoms of MG and develop MG after thymectomy.

However, studies indicate that 1 to 9% of patients with thymoma experience MG after they undergo a thymectomy. This is known as post-thymectomy onset MG (PostTx MG).

Not much is currently known about the clinical characteristics of people who develop PostTx MG.

Thus, a group of Japanese researchers reviewed the clinical information of 158 patients with thymoma‐associated MG. A total of 18 (11%) were found to have PostTx MG.

Results indicated that, among the 11 patients with PostTx MG tested, 82% had anti‐AChR antibodies before the thymectomy was performed. The researchers also found that 50% had electrophysiological abnormalities — impairment with nerve transmission, four patients tested — prior to the surgery.

The clinical characteristics of people with PostTx MG were similar to patients who had MG before the thymectomy — known as pre‐thymectomy onset (PreTx) MG.

Patients with PostTx MG could be further placed into two subcategories based on the duration between the thymectomy and the onset of MG. Those with early‐onset PostTx MG developed MG within six months of surgery, while patients with late‐onset PostTx MG developed the condition after six months.

One-third of patients with PostTx MG experienced thymic tumor relapse. Significantly, late-onset PostTx was associated with thymic tumor relapse.

“In conclusion, our study showed that although patients with thymoma may develop MG after thymectomy, no obvious differences in clinical manifestations between PreTx MG and PostTx MG were observed,” the researchers said.

Looking for anti-AChR antibody levels, or electrophysiological tests in patients with thymic tumor without MG symptoms, may help predict PostTx MG, they said.

The researchers emphasized the necessity of closely following patients who undergo thymectomy to monitor for MG development and thymoma relapse.