Post-thymectomy myasthenia gravis disease severity, relapse rate linked

Researchers analyzed short-term, QMGS-based outcomes in 44 MG patients

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by Andrea Lobo |

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A RISK dial point to high risk.

A greater reduction in disease severity a month after surgery to remove the thymus gland in myasthenia gravis (MG) patients without a thymus tumor is linked with lower disease recurrence, a study in China suggests.

Patients with a reduction of at least 36.7% in the Quantitative Myasthenia Gravis score (QMGS), which quantifies disease severity based on impairments of body function, had a significantly lower relapse rate and later relapse after the surgery than those with a smaller QMGS reduction.

The reduction rate in the QMGS “can be used to predict postoperative recurrence of non-thymomatous MG,” or MG not associated with a thymus gland tumor, the researchers wrote in “The rate of QMGS change predicts recurrence after thymectomy in myasthenia gravis,” which was published in the Journal of Clinical Neuroscience.

MG is an autoimmune disease typically caused by self-reactive antibodies that target proteins needed for the proper function of the neuromuscular junction, the places where nerve cells and muscles communicate to coordinate movements. This leads to symptoms like muscle weakness and fatigue.

Abnormalities in the thymus gland, which produces certain immune cells, are thought to be involved in the antibodies being produced that drive MG. These abnormalities may include an enlarged thymus or a tumor in the thymus gland, called thymoma. This makes surgically removing the thymus one of the therapeutic options for MG.

“Currently, thymectomy is one of the fundamental therapies for MG, especially for thymoma-associated MG (TAMG) and non-thymomatous MG associated with antibodies against the nicotinic acetylcholine receptor (AChR-Abs) and younger than 65 years,” the researchers wrote.

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Thymectomy and MG disease recurrence

Although the procedure can lead to complete MG remission without needing medications, some patients may have residual MG symptoms or disease recurrence after the surgery.

“The identification of patient factors associated with poor responses of MG after thymectomy is crucial for the development of targeted interventions,” wrote a team of scientists in China who retrospectively analyzed the short-term, QMGS-based outcomes in 44 MG patients without thymoma who had a thymectomy at a hospital in Beijing, China, and whether these could predict disease recurrence. QMGS is a 13-item scale where each item is graded from 0 to 3, with higher scores indicating more severe symptoms. The patients (22 men, 22 women) were diagnosed between 2017 and 2020 at a mean age of 45, and had a thymectomy at a mean age of 45.6.

None had a previous thymectomy or were previously on immunotherapy, including plasma exchange, intravenous immunoglobulins (IVIG), corticosteroids and other immunosuppressive therapies, within three months before enrolling. The patients were followed for a mean of 25.7 months, or a little more than two years, and up to more than three years.

Eight patients (18.2%) had a thymectomy alone, while most also received corticosteroids (81.8%) and/or other immunosuppressive therapies (63.6%) to ease symptoms and prevent disease recurrence.

The patients’ mean annualized relapse rate (ARR) was 3.98, meaning nearly four MG relapses a year, before thymectomy and 0.3, or less than one annual relapse, after the procedure. The ARR fell from 3.7 to 0.18 relapses a year in those who had a thymectomy alone.

Fifteen patients (34.1%) recurred in the first year after the procedure, four (16.7%) in the second year, and five (33.3%) in the third year. “During the follow-up period, 21 patients experienced accumulatively 30 total postoperative recurrences,” the researchers wrote.

Moreover, the mean QMGS decreased significantly from 7.66 before a thymectomy to 6.11 at one month after it. The median reduction rate in the QMGS was 25%.

Those with post-surgery disease relapse had a significantly higher QMGS a month after thymectomy (7.67 vs. 4.70) and a significantly lower QMGS reduction rate after a month (7% vs. 34%) than those without disease recurrence.

Predicting disease recurrence

Further analyses showed that a cutoff reduction rate in QMGS of 36.7% at one month after surgery could predict post-thymectomy disease recurrence with an accuracy of 71.2%, a sensitivity of 90.5%, and a specificity of 52.2%. Here, sensitivity referred to this cutoff value’s ability to correctly identify those having a relapse, while specificity referred to correctly identifying those without relapses.

Having a QMGS reduction rate below 36.7% a month after surgery was an independent predictor of post-thymectomy MG relapse, additional statistical analyses showed.

The 14 patients with a QMGS reduction rate of 36.7% or higher after a month were significantly less likely to have an MG relapse relative to the 30 patients with a lower QMGS reduction rate (14.3% vs. 63.3% of the patients). Those with that high reduction rate also had a significantly lower median ARR after surgery (0 vs. 0.44) and had a significantly longer period until relapse (36.6 vs. 12.6 months).

At the final follow-up, most patients (59.1%) achieved minimal disease manifestations or better status relative to before a thymectomy, with no significant differences between groups with high or low QMGS reduction rates at one month post-surgery.

The patients with that high reduction rate were also more commonly men.

The findings suggest “male MG patients without thymoma have greater short-term and long-term benefits after thymectomy,” wrote the researchers.  “This retrospective observational cohort study showed that [reduction rate-QMGS below] 36.7% is a positive predictor of postoperative recurrence,” and a low QMGS reduction rate “was associated with early postoperative recurrence” and higher ARR.