Thymectomy for the treatment of myasthenia gravis is based on several lines of evidence that support a central role of the thymus in the pathogenesis of the disease. Thymomas are present in 10% of patients with myasthenia gravis, and thymectomy is considered to be mandatory to prevent further spread.
Myasthenia gravis (MG) is a neuromuscular disease, meaning that it affects the muscles and the nerves that control them. A disorder causes it in the immune system that causes the body to attack the area of the muscles where the nerves connect to them.
The immune system is the body's natural defense against disease. Usually, when bacteria or other foreign substances enter the body, the immune system produces molecules called antibodies that attack the bacteria.
In people with myasthenia gravis, the immune system produces abnormal antibodies that prevent the muscles from receiving signals from the nerves that tell them when to relax or contract. This causes muscle weakness with symptoms that can include in double vision or blurred vision (eye muscle weakness), drooping eyelids (eyelid muscle weakness), difficulty with speaking and swallowing (throat muscle weakness) and weakness of the limbs.
When the immune system acts against healthy tissue by mistake, it is called an autoimmune disorder, with "auto" meaning "self. So myasthenia gravis is a neuromuscular autoimmune disease.
Myasthenia gravis is most common in young women and older men, but people of any age or either sex can get it.
What causes myasthenia gravis?
Scientists do not entirely understand what triggers the autoimmune reaction in myasthenia gravis, but they do know that the thymus gland plays a role in the disease.
The thymus is a small gland that lies in the front part of the chest, beneath the breastbone, and extends into the lower part of the neck. It is most important early in life during immune system development.
A baby's thymus gland weighs between .7 and 1.1 oz. The gland continues to grow and by puberty weighs 1.1 to 1.8 oz. The thymus gland's job is thought to be completed by puberty, and after that, it decreases in size. Over time, fat replaces portions of the gland. In older people, the thymus weighs only .1 to .5 oz.
Tumors of the thymus gland are called thymomas. Around 10-15 percent of people with myasthenia gravis have a thymoma. Another 60%, however, will have other abnormalities of the gland including thymic hyperplasia (an enlarged gland).
The original association between the thymus gland and myasthenia gravis was made back in the early 1900s when surgeons observed that removal of a thymoma resulted in the improvement in the patient's myasthenia gravis. Ultimately surgeons began removing of the thymus gland in myasthenic patients without thymic tumors, and a similar response was noted.
Research into the causes and treatments of myasthenia gravis will help scientists learn more about the role of the thymus in the disease.
How is myasthenia gravis treated?
The key to treatment of myasthenia gravis begins with an accurate diagnosis. The evaluation is usually directed by a Neurologist and can involve blood tests, nerve testing, and tests involving the administration of medicines to differentiate myasthenia gravis from other diseases of muscles and nerves.
Once the diagnosis has been confirmed, a treatment plan is developed to reduce the number of antibodies causing the disease and/or improving the communication between the nerves and muscles. The ultimate results are improving muscle strength. Medical treatment options include:
Medicines that suppress antibody production or improve nerve signal transmission
Plasmapheresis, a procedure that removes antibodies from the blood
High-dose intravenous immune globulin, the infusion of normal antibodies from donated blood to temporarily modify the immune system.
Surgical treatment is thymectomy, removal of the thymus gland. This is the treatment for patients with thymomas but is also considered for patients with MG who do not have thymomas.
At Cleveland Clinic, the Thoracic Surgeons are part of the treatment team, evaluating patients, and identifying the most appropriate combination of therapies for each.
What are the results of thymectomy?
The goal of thymectomy is to remove the source of abnormal antibody production, causing the disease, thus leading to resolution of symptoms. The benefits of thymectomy are not realized immediately after surgery. Therefore patients will continue with there medical regimen after the procedure to wean those medications over time. Individual response to thymectomy varies depending on the patient's age, response to prior medical therapy, the severity of the disease, and how long the patient has had myasthenia gravis. In general, 70 percent of patients have complete remission or significant reduction in medication needs within a year of the procedure. The other 30 percent of patients who have thymectomy experience no change in their symptoms. According to the American Association of Neurologists, patients who have thymectomy are two times as likely to experience remission as those who have medical treatment alone.
How does a doctor determine which patients with myasthenia gravis should undergo thymectomy?
Thymectomy is recommended for all patients with thymomas and patients under 60 who have mild to moderate muscle weakness due to myasthenia gravis. Thymectomy generally is not used for treating patients with myasthenia gravis that affects only their eyes. Thymectomy appears to be most effective when it is performed six to 12 months after the onset of symptoms. It is essential to talk to your doctor early in your diagnosis about thymectomy as an option for treatment.
How is thymectomy performed?
Several different surgical techniques can perform thymectomy:
Transsternal thymectomy: In this procedure, the incision is made in the skin over the breastbone (sternum), and the breastbone is divided (sternotomy) to expose the thymus. This approach is commonly used for heart surgery. The surgeon removes the thymus through this incision as well as any residual fat in the center of the chest, which may harbor extrathymic cells. This approach is commonly used when the patient has a thymoma.
In this procedure, the incision is made across the lower part of the neck, just above the breastbone(sternum). The surgeon removes the thymus through this incision without dividing the sternum. This is mostly used in patients without thymoma with certain body-types.
Robotic thymectomy and Video-assisted thoracoscopic thymectomy (VATS)
These Minimally invasive techniques use several tiny incisions in the chest. A camera is inserted through one of the incisions, and the surgery is performed with video guidance. The surgeon removes the thymus by using special surgical tools inserted into the other incisions. In a robotic-assisted procedure, the surgeon uses robotic arms to perform the surgery. The goal is to provide the same result as the more invasive transsternal approach with less post-operative discomfort and a quicker recovery.
What are the risks of thymectomy?
Complications are rare, but the risks include:
- Injury lung
- Nerve injury
Your doctor will evaluate your risk based on your age and other medical conditions.
VATS (Video-Assisted Thoracic Surgery)
Video-assisted thoracoscopic surgery (VATS) is a minimally invasive surgical technique used to diagnose and treat problems in your chest.
During a video-assisted thoracoscopic surgery procedure, a tiny camera (thoracoscope) and surgical instruments are inserted into your chest through small incisions in your chest wall. The thoracoscope transmits images of the inside of your chest onto a video monitor, guiding the surgeon in performing the procedure.
Why it's done
Surgeons use the video-assisted thoracoscopic surgery technique to perform a variety of operations, such as:
- Biopsy to diagnose lung cancer, mesothelioma and other chest cancers
- Esophagus surgery (esophagectomy)
- Hiatal hernia repair
- Lung surgery, such as surgery to treat lung cancer and lung volume reduction surgery
- Procedures to remove excess fluid or air from the area around the lungs
- Surgery to relieve excessive sweating (hyperhidrosis)
- Surgery to reduce gastroesophageal reflux disease
- Thymus gland removal surgery (thymectomy)
When compared with a traditional open operation (thoracotomy), video-assisted thoracoscopic surgery may result in less pain and shorten recovery time.
Possible complications of video-assisted thoracoscopic surgery (VATS) include:
- Pneumonia infection
- Temporary or permanent nerve damage
- Anesthesia-related effects
Talk with your doctor about these and other risks of VATS.
How you prepare
You may need to undergo some tests to determine whether video-assisted thoracoscopic surgery (VATS) is a good option for you. These may include imaging tests, laboratory tests, pulmonary function tests, and cardiac evaluation.
If you are scheduled for surgery, your doctor will give you specific instructions to help you prepare.
What you can expect
Usually, people undergoing video-assisted thoracoscopic surgery (VATS) are given a general anesthetic, which means they are asleep during surgery. During video-assisted thoracoscopic surgery (VATS), a doctor puts a breathing tube down your throat into your trachea to provide oxygen to your lungs.
Then a surgeon makes small incisions in your chest and inserts specially designed surgical instruments to perform the procedure.
You may be in surgery for one to two hours, though that can vary depending on your situation.
If you have VATS to biopsy tissue, you may undergo further surgery, depending on the results of the biopsy.