Researchers Identify Potential Novel Indicator of Dysphagia in MG

Researchers of a recent study in Auris Nasus Larynx identified a potential indicator for difficulty swallowing among patients with myasthenia gravis (MG).¹ By studying the swallowing abilities of patients with dysphagia and comparing against those of healthy controls, the researchers determined that respiratory patterns and submental surface electromyography (sEMG) may be used to determine the severity of pharyngeal muscle weakness and fatigability.

A common and disabling symptom of the disease, dysphagia can happen early in the course of MG and it is thought to precipitate myasthenic crisis, creating a need for reliable measures for identifying dysphagia in patients. It’s estimated that nearly 70% of patients with MG havetrouble swallowing.²

“Since swallowing or swallowing-respiration co-ordination varies even in [healthy controls], a comparison of dysphagic status and non-dysphagic status in a dysphagic patient with MG may be important in identifying the essential parameters,” the researchers wrote.¹ “Although previous reports have assessed dysphagia in MG, none have so far evaluated the fatigability of striated muscles.”

Respiratory patterns and submental surface electromyography may be a reliable indicator of dysphagia among patients with myasthenia gravis. | Image credit: Matthieu - stock.adobe.com

The study included 10 patients with MG as well as 22 healthy controls. Among patients with MG, 5 had late-onset disease, 2 had thymoma-associated disease, and 2 had early-onset disease. 

Over 10 minutes, the researchers assessed how patients swallowed 100 mL of water. Using common screening assessments, including QMG swallowing domain score and MGADL swallowing domain scale, the researchers flagged that these measures may not be enough to sufficiently indicate dysphagia. Just 2 patients with MG were positive in the QMG swallowing domain, and among 3 patients with an MGADL score of 3, two were able to drink the water.

Instead, the researchers assessed patients across 4 parameters that indicate irregular swallowing. Dysphagia was characterized by excessive expiratory flows (commonly associated with coughing), clusters of excessive expiratory flows and high inspiratory flows (frequently coming after cough), and prolonged EMG pattern (frequently associated with being unable to swallow), with each of these parameters differing significantly among patients with MG and healthy controls.

Over the 10 minutes, median excessive expiratory flows for patients with MG was 32.5 (range, 0-134) and for healthy controls was 2 (range, 0-29) (P <.001). Three or more consecutive excessive expiratory flows occurred a median of 3 times (range, 0-20) among patients with MG and a median of 0 times (range, 0-2) among healthy controls (P = .003). High inspiratory flows occurred a median of 8 times (range 0-46) among patients with MG and median of 0.5 times (range, 0-7) among healthy controls (P = .010), and median prolonged EMG patterns was 2.5 (range, 0-10) among patients with MG and was 0 (range, 0-3) among healthy controls (P < .001).

Following treatment, excessive expiratory flow, cluster of excessive expiratory flows, and prolonged EMG pattern were significantly improved, nearly at normal levels. Over the same 10-minute assessment time, median excessive expiratory flows decreased to a median of 3.5 (range, 0-36; P = .007), clusters of excessive expiratory flows decreased to a median of 0 (range, 0-1; P = .021), and prolonged EMG patterns decreased to a median of 0 (range, 0-3; P = .013).

“Unfortunately, it is difficult to determine whether subclinical abnormalities could be detected using this method because this study was conducted on MG patients with dysphagia. However, in the post-treatment analysis, there were some patients whose abnormalities were detected in this test, despite the fact that MGADL for dysphagia was 0 (asymptomatic) in these patients,” explained the researchers, noting that further research is required to determine whether subjective symptoms can be indicators of dysphagia.

References

1. Himuro K, Uzawa A, Kawaguchi N, Kanai T, Isono S, Kuwabara S. Quantitative assessment of dysphagia in myasthenia gravis. Intern Med. Published online October 18, 2024. doi:10.2169/internalmedicine.4303-24 
2. Kumai Y, Miyamoto T, Mastsubara K, et al. Assessment of oropharyngeal swallowing dysfunction in myasthenia gravis patients presenting with difficulty in swallowing. Auris Nasus Larynx. 2019;46(3):390-396. doi:10.1016/j.anl.2018.10.004