Nomogram Developed to Predict Risk of Myasthenic Crisis Following Thymectomy

A team of investigators has developed a nomogram they say can help predict which patients with myasthenia gravis (MG) are most likely to experience myasthenic crisis following thymectomy.

The report was published in Annals of Clinical and Translational Neurology.

MG is an autoimmune disorder in which patients experience muscle weakness. In many patients, it begins with ocular symptoms before converting to a generalized form that can impair movement, breathing, and chewing. Some patients experience myasthenic crisis, a life-threatening complication in which worsening muscle weakness leads to respiratory failure and the need for mechanical ventilation. Myasthenic crisis is the leading cause of death in patients with MG, explained the study authors.

Because 30% to 50% of patients with MG have thymoma, and 80% of patients with MG have thymus abnormalities, thymectomy is recommended for patients with generalized acetylcholine receptor (AChR) antibody–associated MG, the most common form of the disease.

Unfortunately, although thymectomy can improve MG symptoms, it can also sometimes induce myasthenic crisis, the authors wrote. Previous research suggests postoperative myasthenic crisis (POMC) typically occurs 7 to 30 days following the operation; however, there is not yet a clear risk-prediction tool for patients undergoing thymectomy. The investigators sought to change that by developing a statistical model they say can help stratify patients with MG into high- and low-risk groups.

The authors enrolled 445 patients in their study, all of whom had MG and were treated at Tangdu Hospital between January 2015 and May 2019. Of those, 43 patients would go on to experience POMC. Five variables were analyzed in the patients: thymus imaging, age of onset, Myasthenia Gravis Foundation of America (MGFA) classification, preoperative treatment regimen, and surgical approach. The authors used logistic regression to develop a nomogram for myasthenic crisis risk. The model had an area under the receiver operating characteristic curve (AUC) of 0.771, indicating a moderate discriminative ability.

Patients placed in the high-risk group had an 8.70-fold higher risk of POMC, the authors said.

Among the risk factors identified in the study, the authors said using a minimally invasive surgical approach appears to lessen the odds of developing POMC. In addition, they said having an MGFA score of 3 or more within a week preceding thymectomy increased the risk of POMC.

Among the study’s limitations, the authors said the retrospective nature of the study could lead to bias, as could the lack of data regarding certain surgery-related variables. They added that surgical approaches, diagnosis and treatment modalities, and nursing techniques can vary widely among hospitals, and so they said their nomogram might not be generalizable to all health care centers. However, the investigators said they are currently working on a prospective multiple-center cohort study to validate the model.

In the meantime, the investigators have made their nomogram publicly available online. They said they believe it can be a useful tool for clinicians.

“This nomogram could assist in identifying patients at higher risk of POMC and determining the optimal surgical time for these patients,” they concluded.

Reference

Ruan Z, Su Y, Tang Y, et al. Nomogram for predicting the risk of postoperative myasthenic crisis in patients with thymectomy. Ann Clin Transl Neurol. Published online March 6, 2023. doi:10.1002/acn3.51752