Thymectomy Found to Reduce Disease Severity in All MG Patients

Thymectomy, or surgical removal of the thymus, can lower medication use and lessen disease severity in people with myasthenia gravis (MG), regardless of age, sex, or medical history, an observational study has found.

Data from the study also indicated that younger female patients with early onset MG, an enlarged thymus,  and mild-to-moderate disease were the ones who benefited most from the procedure.

The study, “Role of thymectomy in myasthenia gravis: Programmatic approach to thymectomy and perioperative management of myasthenia gravis,” was published in the Asian Journal of Surgery. 

In MG, certain immune cells located within the thymus gland are thought to produce self-reactive antibodies that attack nerve-muscle connections, causing muscle weakness in patients. In some patients, the production of autoantibodies is accompanied by thymus abnormalities, which may include a tumor, called a thymoma, or an abnormal enlargement of the gland.

A thymectomy, a procedure in which the thymus is surgically removed, can reduce symptoms, as well as the use of medications in MG patients with and without thymus abnormalities. For this reason, this type of surgery has become one of the main forms of treatment for MG.

Now, researchers investigated the clinical features and outcomes of MG patients who had a thymectomy in the 30-year period between 1988 and 2018 at the Royal Hospital in Muscat, Oman.

The clinical status of each patient was classified using the modified Osserman classification. With that scale, stage I denotes those with purely ocular or eye-related symptoms; stage IIA, those with mild generalized symptoms; stage IIB, those with moderate generalized symptoms; stage III, those with acute fulminant or severe and sudden onset disease; and stage IV, those  with late severe disease.

The patients underwent thymectomy if they had generalized MG, treatment-resistant ocular symptoms, and/or a respiratory crisis.

In that 30-year period, 100 patients — 80% female and 20% male — underwent thymectomy. A total of 10% had a family history of MG. The patients’ mean age was 32, and 72% were younger than 40. 

Half of the patients were diagnosed with MG more than six months after its onset. The most frequently reported symptoms at MG onset were ophthalmoplegia — eye muscle paralysis or weakness — in 75% of the patients, and bulbar symptoms, which are those involving the face and neck, in 57%. Limb weakness and respiratory symptoms both were also reported by 39% of patients.

Prior to the surgery, 5% of patients were classified as Stage I, 39% as Stage IIA, 34% as Stage IIB, and 22% as Stage III. Regardless of stage, all were being treated with either anticholinesterases alone, or in combination with steroids or immunosuppressants like azathioprine.

After undergoing thymectomy, 21 patients no longer required any medications. The mean follow-up period after surgery was six years, ranging from two to 12 years. During follow-up, 21% of the patients achieved complete remission, while 76% had significant clinical improvement. A total of 3% experienced no improvements.

Post-surgery thymus tissue analysis revealed that 57% of the patients had hyperplasia or enlargement of the thymus, 18% had thymus shrinking, and 2% had tissue atrophy or wasting.

All 100 patients survived the procedure. Wound infections (4% of patients), fluid in the lungs (2%), and myasthenic crisis (2%) were reported as post-surgery complications.

“Thymectomy can reduce patient’s need for medication and reduce the severity of MG regardless of age, sex, severity, or length of sickness, or thymic masses,” the investigators wrote.

They also noted that in this particular study, “younger people, those who had early onset severe MG, female and … thymic hyperplasia and with Osserman classification IIA and IIB benefited the most from the surgical intervention.” However, they also acknowledged that these factors may be different in other patient populations.