Thymectomy May Be Better for Early-onset MG

Thymectomy – surgical removal of the thymus gland — may be a better option for treating patients with early-onset non-thymomatous myasthenia gravis (MG), a study has found.

According to study data, the surgical procedure did not confer an added benefit over non-invasive treatment options for patients with late-onset disease.

The study, “Effects of thymectomy on late-onset non-thymomatous myasthenia gravis: systematic review and meta-analysis,” was published in the Orphanet Journal of Rare Diseases.

MG is a neuromuscular disease that occurs when self-reactive antibodies drive the immune system to attack the body’s own neuromuscular junctions — the region where muscles and nerves come into contact and communicate.

While the exact origin of these self-reactive harmful antibodies remains poorly understood, researchers think that abnormalities in the thymus gland — an organ that is part of the immune system — may trigger or help maintain their production. For this reason, thymectomy is thought to be a possible treatment for MG.

Depending on the age of disease onset, MG can be classified into two types: early onset MG, when it arises before the age of 40–50 years; and as late onset MG, when it arises after the age of 40–50 years.

Some authors instead use the ages of 60–65 as a cutoff point to distinguish early-onset from late-onset MG. Previous research has shown that age at disease onset may affect a patient’s clinical course following a thymectomy.

In this study, researchers focused on a particular group of patients they called non-thymomatous — those without a thymoma, or tumor in the thymus gland — to study the effects of thymectomy on those with late-onset MG.

They had two major goals. First, they wanted to determine if the likely course of thymectomy is the same for patients with early- and late-onset MG. Second, they wanted to assess if thymectomy might have an added benefit over conservative (non-invasive) treatment options for patients with late-onset MG.

Conservative treatment options included anticholinesterases (medications that increase the levels of the neurotransmitter acetylcholine, which is needed for muscle contraction), corticosteroids (medications that suppress immune and inflammatory responses), and other immunosuppressants.

Using a meta-analysis — a method of analysis that combines data from multiple studies — researchers collected information from a total of 12 studies. To be included in the meta-analysis, studies had to consider a cutoff age of 40–60 years to distinguish individuals with early- from those with late-onset MG.

Of the 12 studies, nine compared the post-thymectomy outcomes in a total of 766 patients with early-onset MG versus a total of 230 patients with late-onset MG.

Compared with patients with late-onset MG, those with early-onset MG were almost twice as likely to achieve complete stable remission, or see all signs and symptoms of the disease disappear for at least one year while not taking any MG-specific medication.

Only five studies — involving 430 patients with early-onset MG and 139 with late-onset MG — provided data on symptom improvement following a thymectomy. However, there was no difference in symptom improvement between the two groups.

To tackle the second goal, researchers analyzed data from three studies, which included a total of 216 late-onset MG patients. Of those, 75 had undergone thymectomy and 141 had received conservative treatment.

Compared with conservative treatment, thymectomy offered no added benefits in terms of increasing a patient’s chance of achieving complete stable remission or pharmacological remission. In order to achieve pharmacological remission, a patient must have no signs or symptoms of the disease for at least one year while continuing to receive some form of MG treatment.

“We observed that late-onset [non-thymomatous MG] patients had a lower chance of achieving [complete stable remission] after thymectomy than early-onset patients,” the researchers wrote, adding that late-onset MG patients “did not obtain any benefits from thymectomy versus conservative treatments.”

“Thymectomy in late-onset [non-thymomatous MG] patients should therefore be performed with caution, and further investigation into cutoff ages is needed to deliver specific therapeutic strategies,” they concluded.