Myasthenia gravis is most often associated with skeletal muscle weakness, which can be exacerbated with exercise or repetitive use.
Myasthenia gravis can also negatively impact cardiac health. Studies indicate that dysfunction of the cardiac autonomic nervous system is widely prevalent among patients with myasthenia gravis, a condition that causes abnormal baroreflex sensitivity. In addition, cardiac dysfunction can mean variability in a patient’s heart rate and blood pressure.
Read more about myasthenia gravis etiology
In the Journal of Clinical Medicine, a team of Chinese researchers led by Chen conducted a study to investigate the prevalence of myocardial injury among patients with myasthenia gravis. They chose cardiac troponin as a biomarker of myocardial injury; studies indicate that cardiac troponin is a highly sensitive indicator of acute injury to the myocardium.
The research team retrospectively searched patient records who had a diagnosis of myasthenia gravis at the West China Hospital of Sichuan University. Records from January 2011 to September 2021 were accessed. They included patients with a diagnosis of myasthenia gravis confirmed by a positive serological test for autoantibodies, a positive neostigmine test, or abnormal repetitive nerve stimulation. They excluded patients with pre-existing heart disease.
The research team looked into the blood investigations conducted at the time of the patients’ hospital admission. The reference range for cardiac troponin levels is 0 to 14 ng/L; anything above that figure signifies myocardial injury, regardless of new abnormalities on echocardiography or electrocardiography.
“The [troponin] levels were deemed necessary to be performed based on the cardiac-like clinical symptoms, such as chest pain, chest tightness, dyspnoea, fatigue, palpitations, or syncope,” Chen and colleagues wrote. “The changes on the electrocardiogram, echocardiography, and coronary angiography were used to exclude coexisting heart disease, such as ischaemic myocardial injury.”
The research team found 336 patients with myasthenia gravis who had their troponin levels measured. Among the 336 patients, 192 had elevated troponin levels. A total of 38 patients died; 37 had elevated troponin levels. Chen et al reported that myocardial injury was an independent risk predictor of death during hospitalization, even after adjusting for confounding factors such as age, sex, infection, and thymoma.
The research team also discovered that myocardial injury is often overlooked in patients with myasthenia gravis, probably because patients are often asymptomatic or present with nonspecific symptoms such as chest tightness and fatigue. They also discovered that most patients were not screened for myocardial injury, meaning the condition goes undetected and untreated.
Case Study: Sudden Cardiac Death in a Young Man
In Mathews Journal of Case Reports, Ghayyem and colleagues presented the case study of a young man with myasthenia gravis who died suddenly from a heart attack.
A 37-year-old man with a background of myasthenia gravis presented with mild exertional dyspnea. He also had a history of hypertension, Hashimoto thyroiditis, and depression.
The patient’s vital signs were normal. Mild crackles could be heard in the lower lobes of both lungs. A chest x-ray revealed patchy bilateral consolidation. The patient was admitted for closer observation. An echocardiography test was normal.
The patient’s dyspnea worsened in the following hours, which soon progressed to tachypnea and respiratory distress. He was put on an oxygen mask (5 liters per minute). An arterial blood gas indicated respiratory acidosis. An endotracheal intubation was performed, and the patient was tested for SARS-Cov2.
The patient had a chest computed tomography (CT) scan, revealing bilateral multifocal ground-glass opacities with mild right pleural effusion. A thoracocentesis was performed, which was suggestive of an exudative pleural fluid (lactate dehydrogenase: 330 IU/L; protein: 4.5 g/L).
“We considered both infection and [myasthenia gravis] as the leading causes of the patient’s respiratory failure, so he underwent plasmapheresis on the same day combined with 2 g/kg/day [intravenous gamma-globulin],” Ghayyem et al wrote.
The patient received lopinavir/ritonavir 400/100 mg and hydroxychloroquine 400 mg. He was also prescribed prophylactic anticoagulation. An echocardiography showed normal cardiac function.
The patient was then found to be positive for SARS-Cov2. Despite his physicians’ best efforts, his condition continued to deteriorate. A few hours later, he went into cardiac arrest. Resuscitation efforts were unsuccessful, and the patient died.
Read more about myasthenia gravis prognosis
The patient’s physicians theorized that infection served as a trigger for the patient’s myasthenia gravis and speculated that the patient experienced myocarditis following viral infection, leading to sudden cardiac death.
While this case study was complicated by SARS-Cov2 infection, it highlights how myocardial injury can occur due to an acute exacerbation of myasthenia gravis. Interestingly, echocardiography failed to detect any signs of cardiac abnormalities. Nevertheless, physicians should recognize that patients with myasthenia gravis are vulnerable to myocardial injury and take appropriate action when the patient is critically ill.
“Older age, infection, myasthenic crisis, thymoma, and [immune checkpoint inhibitor] therapy were independently associated with myocardial injury in [myasthenia gravis] patients,” Chen and colleagues wrote. “Careful attention should be paid to myocardial injury in [myasthenia gravis] patients.”
References
Chen H, Kong L, Zhang Y, et al. Myocardial injury in hospitalized patients with myasthenia gravis. J Clin Med. Published online November 30, 2022. doi:10.3390/jcm11237106
Ghayyem M, Haseli S, Yaghmaei S. COVID-19 and sudden cardiac death in a young man with myasthenia gravis. MJCR. Published online July 1, 2021.
