MG at Advanced Stage Follows Thymus Surgery in Older Man
A man developed myasthenia gravis (MG), which quickly progressed to an advanced stage, shortly after surgery to remove a tumor in the thymus gland, according to a report from China.
Post-surgical MG is rare and its rapid severity even rarer, its scientists noted, and this man’s MG diagnosis was more difficult because he also developed a serious lung infection.
Being aware of the risks of lung infections like pneumonia, which can be common after a thymectomy, masking a disorder like myasthenia gravis is important, they added, as it delays “the best opportunity” for proper treatment.
The report, “Refractory post-thymectomy myasthenia gravis with onset at MGFA stage V: a case report,” was published in the Journal of Cardiothoracic Surgery.
A thymectomy is a surgery to remove the thymus, a gland-like organ located in the chest that is part of the immune system, possibly due to a thymoma, or tumor in the thymus.
While a thymectomy is a main way of treating myasthenia gravis, the condition can in rare cases also follow this surgery. Its mechanism of onset is unclear, the scientists wrote, and the time from surgery to the start of MG symptoms can vary widely, from a few days to years.
Scientists at The First Affiliated Hospital of Chongqing Medical University reported the case of a 70-year-old who developed MG that quickly advanced after a thymectomy.
The man came to the hospital because of chest pain. A CT scan revealed the presence of a mass in the area of the thorax that contains the thymus.
A decision to perform a thymectomy was made based on the suspicion that the mass could be a thymoma, which it turned out to be. The thymoma was type B2 under the World Health Organization (WHO) classification and stage III under the Masaoka staging classification. This means that the thymoma had many lymphocytes, a type of white blood cell, and that it had invaded a large vessel, the pericardium (the membrane around the heart), or the lungs.
The man was discharged from the hospital without complications nine days after his surgery.
Five days later, he returned with difficulty breathing (dyspnea) and a fever. A CT scan showed the lungs had a patchy appearance, but no evidence of a reoccurring thymoma. He was diagnosed with pneumonia, an inflammation of the lungs caused by an infection.
He lost consciousness in the emergency room, and a test to measure the amount of oxygen and carbon dioxide in the blood revealed respiratory failure due to too little carbon dioxide being removed through respiration. He was placed on mechanical ventilation with intubation, a tube placed into the windpipe or trachea.
A sample of lung fluid revealed the presence of Acinetobacter baumannii, a type of bacteria. The infection was treated with antibiotics, and the man’s condition improved.
“However, we failed to wean him off ventilation,” the researchers wrote.
A neostigmine test was negative, meaning his symptoms did not ease with the medication. Neostigmine is an anticholinesterase medication that improves the transmission of signals from nerve to muscle cells by increasing the levels of signaling molecule called acetylcholine. A marked improvement in a patient’s condition following the administration of neostigmine may indicate the presence of MG.
Levels of antibodies against the acetylcholine receptor (AChR), which target AChR on muscle cells to cause muscle weakness in MG patients, were slightly elevated. Based on this finding, MG was suspected.
“There have been … cases of post-thymectomy MG with onset at stage I–II on the basis of Myasthenia Gravis Foundation of America (MGFA) classification, but rarely at stage V,” the researchers wrote.
MG can weaken muscles involved in breathing, and patients with stage V disease require intubation, with or without mechanical ventilation. Those with stage I–II disease typically experience mild muscle weakness that does not compromise their ability to breathe.
To help wean the man off mechanical ventilation, doctors performed a tracheostomy, a procedure to create an opening in the windpipe to provide an alternative airway for breathing.
He was also given Mestinon (pyridostigmine), an anticholinesterase medication often used to treat MG. However, he experienced diarrhea as a side effect, and treatment was stopped. As a result, he was placed on mechanical ventilation again.
Intravenous immunoglobulin (IVIG) was suggested, but refused initially due to its high cost. As an alternative, steroid pulse therapy was started, but its effect was “slow and poor.” Plasma exchange, also known as plasmapheresis, and IVIG were then started.
Four months after his admission, the man was weaned off mechanical ventilation and being treated with tacrolimus, an immunosuppressant, at a low daily dose.
Prior to a thymectomy, even in asymptomatic patients, tests to determine antibody levels against AChR “should be done to identify subclinical MG, so that the surgeons and anesthesiologists could take measures in advance” to avoid the disorder’s development and progression post-surgery, the scientists advised.
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