Signs and Symptoms of Thymoma
Thymomas present with a characteristic triad: local compressive symptoms (chest pain, cough, dyspnea), myasthenia gravis in 30-50% of cases, or are discovered incidentally in asymptomatic patients. 1
Patient Demographics
- Thymomas typically occur in adults aged 40-70 years and are exceedingly rare in children or adolescents. 1, 2
- Unlike most malignancies, alcohol, tobacco smoking, and ionizing radiation are not risk factors for thymoma development. 2
Local Compressive Symptoms
When symptomatic, patients present with:
However, a substantial proportion of patients (approximately 30-40%) remain completely asymptomatic, with thymoma discovered incidentally on chest imaging performed for unrelated reasons. 2, 3
Myasthenia Gravis: The Hallmark Paraneoplastic Syndrome
Myasthenia gravis is the most common and clinically significant paraneoplastic syndrome, occurring in 30-50% of thymoma patients. 1, 4
Specific myasthenia gravis symptoms to assess include:
- Drooping eyelids (ptosis) 1, 5
- Double vision (diplopia) 1, 4
- Difficulty climbing stairs 1, 5
- Muscle weakness 4
- Hoarseness 1, 5
- Dyspnea 1, 5
- Drooling 1
- Dysphagia 4
The frequency of myasthenia gravis varies by histological subtype: type B2 and B3 thymomas (50% each), type B1 (40%), type AB (20%), and type A (15%). 4
Critically, myasthenia gravis associated with thymoma is almost always accompanied by anti-acetylcholine receptor antibodies, making this the key diagnostic marker. 5, 4
Other Paraneoplastic Syndromes (Less Common)
Beyond myasthenia gravis, other paraneoplastic syndromes occur in less than 10% of thymoma patients collectively: 2, 4
- Pure red cell aplasia (approximately 5% of cases) - presents with severe anemia and absent reticulocytes 2, 4, 6
- Hypogammaglobulinemia/Good syndrome (approximately 5% of cases) - presents with recurrent infections 2, 4, 6
Critical Diagnostic Pitfall
The combination of myasthenia gravis symptoms with an anterior mediastinal mass on imaging is so specific for thymoma that surgical biopsy should be avoided if the tumor appears resectable, as biopsy is unnecessary and may risk pleural seeding. 1, 4
All patients with suspected thymoma—even those without overt myasthenia gravis symptoms—must have serum anti-acetylcholine receptor antibody levels measured preoperatively to identify subclinical myasthenia gravis and prevent respiratory failure during surgery. 1, 2, 5
Clinical Presentation Pattern
The clinical presentation follows a predictable pattern:
- Approximately 30-40% of patients are asymptomatic (incidental finding) 2, 3
- Approximately 30-50% present with myasthenia gravis 1, 4
- The remaining patients present with local compressive symptoms 1
Importantly, approximately 20% of mortality in thymoma patients is directly attributable to myasthenia gravis itself rather than tumor progression, emphasizing the clinical significance of this paraneoplastic syndrome. 1