MG Onset Follows Surgery to Remove Thymus in Case Study

Patricia Inacio, PhD avatar

by Patricia Inacio, PhD |

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In an older woman, myasthenia gravis (MG) onset followed surgery to remove a thymoma, or tumor of the thymus, a case study reported.

Doctors should actively check for MG symptoms in patients with a thymoma before and after surgery, and measure the levels of self-reacting antibodies against acetylcholine receptors, the most common autoantibodies found in MG, its scientists advised.

The study, “Post-thymectomy myasthenia gravis: a case report and systematic review of literature,” was published in the journal BMJ Case Reports.

MG, an autoimmune disease characterized by weakness and fatigue, is driven by self-reactive antibodies that mistakenly attack proteins in the neuromuscular junction — the place where nerve endings come into contact and communicate with muscle fibers.

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Acetylcholine receptors (AChRs) are the most frequent target in MG. More rarely, patients can produce antibodies targeting another protein called MuSK, which is also involved in nerve-muscle communication.

While the specific events that cause production of these self-reacting antibodies are still poorly understood, abnormalities like tumors in the thymus gland — an organ in the chest that is part of the immune system — are thought to play a role.

thymectomy, or surgically removing the thymus, is often a treatment of choice for MG. However, MG symptoms sometimes first arise after this surgery.

Scientists in the U.K. described the case of an 82-year-old woman who developed fatigue, ptosis (eyelid droopiness) and dysarthria (slurred or slow speech) due to muscle weakness within three months after undergoing a thymectomy.

The surgery, performed in March 2020, was the treatment of choice after she started experiencing shortness of breath (dyspnea) that continued to worsen for several months. A chest PET scan revealed a mass, and analysis of the tumor after its removal confirmed it to be a type AB thymoma.

The woman recovered well after surgery with complete resolution of her dyspnea. Within three weeks she was fully mobile and independent.

In May, she was again admitted to a hospital after six weeks of reduced mobility and fatigue. Over 10 days she had intermittent slurred speech and droopy eyelids, but no swallowing difficulties (dysphagia).

A neurological exam showed signs of moderate motor speech disorder, accompanied by a weak cough and droopy eyelids. Muscle weakness involving the legs and arms was also evident, but no muscle wasting.

Blood tests showed she had low levels of vitamin D, but markers of kidney and thyroid function were normal. Her spine was also normal on CT and MRI scans. However, further analyses found she was positive for anti-AChR antibodies and negative for anti-MuSK antibodies. Chest CT and PET scans showed no signs of residual thymic tissue or thymoma.

Considering these findings, a neurologist diagnosed her with generalized MG. She started treatment with pyridostigmine and prednisolone, a corticosteroid. Pyridostigmine (marketed as Mestinon, Regonol, or as generic brands) is the most commonly prescribed acetylcholinesterase inhibitor used to treat MG.

She returned to her home after a short hospital stay. By the time of her first follow-up exam one month later, her vision and speech difficulties had resolved.

MG appearing after removal of thymoma was first reported in 1951, and occurs in 1.5%–28% of thymoma patients without
MG preoperatively,” the scientists wrote.

Clinicians need to “actively look out for myasthenic symptoms in asymptomatic thymoma patients before and after thymectomy with regular follow-up postoperatively so that early detection and treatment of myasthenia gravis can prevent deterioration,” they concluded.

“There is a need to investigate late-onset post-thymectomy myasthenia gravis patients for thymoma relapse as a cause of new symptoms,” they added, noting that measuring the levels of anti-AChR antibodies before surgery can be helpful in determining a patient’s likely outcomes.