Thymus Tumor Elevates Risk of Ocular MG Becoming Generalized, Case Series Finds

Thymoma, a tumor of the thymus gland that can be benign or malignant, elevates ocular myasthenia gravis (MG) patients’ risk of developing a generalized form of the disease, a case series in Germany reported.

Within two years, ocular MG evolved to generalized MG in most of the patients under study; thymoma was the only risk factor significantly associated with this event. Data suggests, however, that treatment with corticosteroids might prevent MG generalization in some patients.

The study, “Generalization after ocular onset in myasthenia gravis: a case series in Germany” was published in the Journal of Neurology.

About half of MG patients initially present with eye symptoms, or ocular MG, but within two years most of those  — about 60% — will develop secondary generalized MG, a more severe form of the disease marked by muscle weakness in different parts of the body.

The factors that predispose or prevent the process of disease spread are still under debate. To that end, researchers at the Charité University Hospital Berlin, Germany, conducted a study with the goal of identifying risk factors for MG generalization.

They retrospectively reviewed clinical parameters, thymic pathologies (disease) and medical treatments of MG patients with ocular symptoms only, at disease onset, who underwent robotic-assisted thymectomy (thymus gland surgical removal) as a treatment for MG in their hospital.

From an initial population of 572 MG patients, they selected a final sample of 180 subjects who fit the study. Mean follow-up of these patients was nearly two years (23.6 months).

The study population consisted of 116 patients with early-onset MG and 64 late-onset MG; there were more women (105; 58.3%) than men (75; 41.7%).

Over this period, 110 of the 180 patients (61.1%) eventually developed generalized MG, while in 70 (38.9%), the disease remained restricted to the eye. The median time between eye symptom onset and conversion to generalized MG was nine months.  Although most patients converted to generalization within two years after symptom onset, 17 (15.5%) patients did so later on.

After analyzing several clinical parameters, thymoma was the only significant risk factor associated with MG generalization. Patients with thymoma were 65.9% more likely to see their disease become generalized than those without a thymus tumor.

Although overall corticosteroids use did not influence the risk of MG generalization, a group analysis suggested that it might decrease by more thant half (58.6%) the changes to generalized disease, specifically in patients who displayed enlargement of the thymus, or thymus hyperplasia.

“Although previous studies have identified thymoma as a risk factor, this was the first time thymoma has been identified as a risk factor for generalization in a large pathologically confirmed series,” researchers stated, adding that in their study it was not possible to stratify ocular MG patients to “high-risk” or “low-risk” groups.

“Further prospective studies are needed to validate this risk prediction model,” they said, adding that “treating ocular myasthenia patients with corticosteroids may reduce the risk of generalization, which needs to be validated in further studies.”