Myasthenia gravis (MG) is an autoimmune disorder characterized by fluctuating muscle weakness and fatigue, particularly affecting muscles that control eye movements, facial expressions, swallowing, and breathing [1,2]. The disease ranges from mild to life-threatening, especially when it impacts respiratory muscles [1]. Although primarily a neuromuscular junction disorder, MG’s systemic effects, including its influence on sleep, are increasingly acknowledged [3-5]. One area of emerging interest is the potential link between MG and obstructive sleep apnea (OSA) [6-8], a sleep disorder that features repetitive episodes of upper airway obstruction that result in frequent arousals, oxygen desaturation, and sleep disruption. OSA leads to critical health consequences such as daytime sleepiness, hypertension, cardiovascular disease, stroke, and reduced quality of life (QOL) [9].

While the prevalence of OSA is well-documented in the general population, it is less understood in patients with neuromuscular disorders, such as MG. The STOP-BANG questionnaire, a common screening tool for OSA [10], has been applied across various populations, but its effectiveness in MG patients remains underexplored. Given the overlapping symptoms between MG-related issues and OSA features, such as fatigue and excessive daytime sleepiness (EDS) [5,11], determining the prevalence and clinical features of OSA in this patient population is essential. This study aims to evaluate the prevalence of OSA risk in MG patients using the STOP-BANG questionnaire and to explore the relationship between OSA risk, daytime sleepiness, and QOL in these individuals.

The retrospective study was conducted at the Department of Neurology, Inje University Busan Paik Hospital, a renowned tertiary hospital in Korea. A total of 73 consecutive adult MG patients who visited the neurology department in 2022 were enrolled. The diagnosis of MG was confirmed through clinical evaluation and diagnostic tests. Only patients aged 18 years and older with a confirmed diagnosis of MG were included. Exclusion criteria included patients experiencing a myasthenic crisis, and those with severe psychiatric, advanced cardiopulmonary, or renal diseases.

Data were obtained from the patients’ electronic medical records and included demographic details such as age, sex, and body mass index (BMI), as well as disease-related information such as the duration of MG, history of thymectomy, and the use of pyridostigmine or immunosuppressants. The severity of MG was assessed by a single peripheral neuropathy specialist using the Myasthenia Gravis Foundation of America system, which classifies patients as having either ocular or generalized MG.

The primary outcome, OSA risk, was evaluated using the Korean version of the STOP-BANG questionnaire. This assessment tool comprises eight items relating to snoring, tiredness, observed apneas, blood pressure, BMI, age, neck circumference, and sex, with scores ranging from 0 to 8. Patients were categorized into low (score <3), intermediate (score 3–5), and high (score ≥5) risk groups for OSA [10]. For a more accurate reflection of obesity characteristics in Koreans, the BMI threshold was reduced from 35 kg/m2 to 30 kg/m2, and the criteria for neck circumference were adjusted to 36.6 cm for men and 32.3 cm for women [12,13]. Daytime sleepiness was assessed via the validated Korean version of the Epworth Sleepiness Scale (ESS), where a score of 11 or higher indicates EDS [14]. QOL was measured using the MG Activities of Daily Living (MG-ADL) scale [15] and Revised Scale of 15-Item Myasthenia Gravis Quality of Life Scale (MG-QOL15r) Scale [16], with higher scores reflecting poorer ADL and QOL.

Descriptive statistics summarized the demographic and clinical characteristics. Continuous variables were presented as means and standard deviations, while categorical variables were depicted as frequencies and percentages. We compared the low and intermediate/high OSA risk groups using the independent t-test or Mann-Whitney test for continuous variables and the chi-square test or Fisher’s exact test for categorical variables. All analyses were conducted using STATA version 14.2 (StataCorp LP, College Station, TX, USA), with statistical significance defined as a p-value of <0.05.

Out of 73 MG patients, one was excluded due to a missing STOP-BANG questionnaire, resulting in 72 participants included in the study. Table 1 presents the demographic and clinical characteristics of these patients. The mean age was 57.3±16.7 years and 27 patients (62.5%) were females. Among the cohort, 58.3% were diagnosed with generalized MG, and 91.7% were treated with pyridostigmine, while 55.6% were receiving immunosuppressants. The average duration of MG was 8.7±8.8 years. According to the STOP-BANG questionnaire, 57 patients (79.2%) were at intermediate to high risk for OSA (STOP-BANG score ≥3), and 21 patients (29.2%) were at high risk (STOP-BANG score ≥5). The mean STOP-BANG score for all participants was 3.7±1.5. There were no statistically significant differences in age, sex, BMI, or disease duration between patients in the low-risk group and those in intermediate- to high-risk groups. However, those in the intermediate to high risk group had a significantly higher ESS score (6.73±5.15) compared to the low-risk group (3.40±3.98, p=0.02). Despite the higher risk of OSA, there were no significant differences between the groups in terms of other clinical measures, such as MG-ADL and MG-QOL15r scores.

The study finds nearly 80% of the MG patient cohort at intermediate to high risk for OSA based on the STOP-BANG questionnaire. The significant association between higher STOPBANG scores and increased ESS scores indicates that patients at greater risk for OSA experience more pronounced daytime sleepiness, which could adversely affect their QOL.

The observed high prevalence of OSA risk mirrors findings in Western populations [6,8], where OSA is frequently reported among patients with neuromuscular diseases, including MG. However, the absence of significant differences in other clinical and QOL measures between OSA risk groups prompts further exploration of OSA’s broader impact on MG patients. For instance, a study employing portable PSG on 28 MG patients documented typical OSA in 12 participants but found no significant link between MG clinical parameters and nocturnal breathing disturbances [17]. Another cross-sectional study noted that OSA was more common in older male MG patients with higher BMI and those who had used corticosteroids [6], but it did not correlate significantly with MG severity or duration.

Several factors may underlie the high OSA risk in MG patients. Muscle weakness, particularly in respiratory and pharyngeal muscles, may predispose these individuals to OSA [9], along with diaphragm weakness that reduces ventilatory capacity during sleep, exacerbated by reduced activity of accessory respiratory muscles [18]. Additionally, muscle fatigue, which aggravates with repeated use, including respiratory muscles [1,19], may worsen overnight, leading to more severe and frequent apneic events. Nonetheless, this study did not find significant variations in conventional OSA risk factors between low and high-risk groups, suggesting that MG-specific elements may play a predominant role.

While the STOP-BANG questionnaire is a valuable tool for OSA screening, its suitability for MG patients necessitates further examination. The symptomatic overlap between MG and OSA, such as fatigue and sleepiness, could complicate STOP-BANG score interpretations in this group. Moreover, the tool’s reliance on self-reported symptoms like tiredness might be less reliable in MG patients due to their distinct clinical manifestations.

This study has several limitations, including its relatively small sample size and retrospective design, which restrict the generalizability of the findings. Additionally, the exclusive use of the STOP-BANG questionnaire for OSA risk assessment, instead of polysomnography (PSG), could be a constraint. Although known for high sensitivity [20], the STOP-BANG questionnaire’s lower specificity might have led to OSA risk overestimation. Notably, of the 57 patients categorized as moderate to high OSA risk by STOP-BANG, only 6 underwent in-lab PSG, with 5 diagnosed with OSA.

In summary, this research demonstrates a substantial prevalence of OSA risk among Korean MG patients, with prominent links between higher STOP-BANG scores and increased daytime sleepiness. While the STOP-BANG questionnaire remains a practical OSA screening tool, its application to MG patients requires further validation.