What are the indications for thymectomy (surgical removal of the thymus gland) in patients with myasthenia gravis or thymoma?

Thymectomy Indications

Absolute Indication: Thymoma

Thymectomy is mandatory in all patients with thymoma, regardless of myasthenia gravis (MG) status. 1, 2

• Approximately 30-50% of thymoma patients have concurrent MG, and critically, 20% of mortality in thymoma patients is directly attributable to MG itself rather than the tumor 2
• Complete thymectomy with total removal of all thymic tissue is essential, as local recurrences occur after partial procedures 2
• All patients with suspected thymoma must have serum anti-acetylcholine receptor (AChR) antibody levels measured preoperatively to prevent respiratory failure during anesthesia 2, 3
• Prior to surgery, patients must be evaluated for MG symptoms and medically optimized to prevent perioperative respiratory complications 1, 2

Strong Indication: Non-Thymomatous Myasthenia Gravis

Thymectomy should be performed in AChR-positive MG patients, particularly those with specific age-based and immune-based characteristics, as it substantially reduces clinical symptoms. 1, 2

Patient Selection Criteria for Optimal Outcomes:

Age and Disease Duration:

• Younger patients (<50 years) achieve significantly better outcomes 4, 5, 6, 7
• Patients with symptom duration <2 years before surgery have higher remission rates 5, 6
• Age >60 years is associated with poorer response 6

Disease Severity:

• Patients in Osserman class I and IIA benefit most, with remission rates approaching 81% at 89 months 5, 7
• Mild to moderate generalized MG (not just ocular) shows favorable outcomes 4, 5, 7
• Patients requiring only low-dose pyridostigmine preoperatively have better prognosis 6

Immunologic Profile:

• AChR-positive patients are the primary candidates, as thymectomy terminates provision of high-affinity anti-AChR antibody-producing cells from thymus to peripheral organs 2

Expected Outcomes:

• Complete stable remission (CSR): 34-46% of patients 5, 8, 7
• Pharmacological remission (symptom-free on minimal medication): 24-33% 5, 8, 7
• Overall improvement rate: 68-96% of patients benefit from surgery 4, 5, 6, 7
• Remission rates increase with longer follow-up duration, with continued improvement beyond 3 years 5, 8

Factors Associated with Poor Response:

• Presence of thymoma (less favorable outcome than non-thymomatous MG) 4, 6
• Thymic atrophy on histopathology 6
• Preoperative use of high-dose corticosteroids 6
• Osserman stage III-IV disease 6

Surgical Approach Requirements

Total "maximal" thymectomy is the preferred technique, as thymic tissue is widely distributed in the neck and mediastinum. 1, 2, 5

• En bloc transcervical-transsternal approach ensures complete removal of all thymic tissue including perithymic fat 2, 5
• Surgical biopsy should be avoided if resectable thymoma is strongly suspected based on clinical and radiologic features 1
• Transpleural biopsy approach must be avoided 1
• During surgery, pleural surfaces must be examined for metastases 1
• Complete resection may require removal of adjacent structures (pericardium, phrenic nerve, pleura, lung), but bilateral phrenic nerve resection should be avoided due to severe respiratory morbidity 1

Minimally Invasive Considerations:

• Not routinely recommended due to lack of long-term data 1
• May be considered only in specialized centers by experienced surgeons if all oncologic goals can be met as in standard procedures 1

Critical Preoperative Management

Neurologist consultation and MG treatment optimization are mandatory before surgery. 1, 2, 3

• Medical control of MG symptoms must be achieved prior to surgical resection 1
• Particular care with anesthetic agents is required given potential respiratory muscle weakness 1, 2
• Patients should be evaluated for signs of generalized disease, as 50-80% with initial ocular symptoms develop generalized MG within a few years 1, 3

Reoperation Indications

For patients with persistent or recurrent severe symptoms after previous transcervical or submaximal transsternal resections, reoperation with maximal thymectomy technique is recommended. 5

• Residual thymus is found in all patients requiring reoperation 5
• Response to reoperation is favorable but slower than primary surgery, likely due to more severe and longer-duration symptoms 5

Common Pitfalls to Avoid

• Do not perform partial thymectomy in MG patients - incomplete removal leads to local recurrences and suboptimal outcomes 2, 5
• Do not proceed to surgery without preoperative AChR antibody testing in suspected thymoma patients - risk of intraoperative respiratory failure 2, 3
• Do not delay thymectomy in appropriate candidates - shorter symptom duration correlates with better outcomes 5, 6
• Do not use minimally invasive approaches without extensive experience - risk of incomplete resection 1