A 47-year-old woman is admitted to the hospital for progressive weakness, fatigue, double vision, and most recently shortness of breath. She reports experiencing similar symptoms at least twice in the past year, but then symptoms were less severe and lasted only a few days before improving spontaneously. She denies a recent illness or unusual exposures. In addition, she denies cough, chest discomfort or pain, weight changes, fever/chills, or abdominal pain.
On exam her strength is 4/5 to 5/5 in most major muscle groups, and left sided ptosis is noted. Her pupils are symmetric and demonstrate normal light reflexes. The remainder of the physical exam is normal.
A complete blood count and metabolic panel returns within normal ranges. Her oxygen saturation is 98% on room air. A CXR reveals clear lung fields with some haziness of the right perihilar region. A transthoracic echocardiogram reveals normal systolic and diastolic function and no valvular abnormalities. A CT scan of the chest shows a large homogeneous mass involving the anterior mediastinum.
Regarding the mass, what is the most likely diagnosis?
Answer: C – Thymoma
Key point: Know the differential diagnosis of an anterior mediastinal mass.
Recognize that thymomas are associated with a wide variety of paraneoplastic disorders, the most common of which is myasthenia gravis.
Discussion: Mediastinal masses fortunately can be categorized by compartmental location. Anterior mediastinal masses are usually lymphoma, thyroid, thymoma, or teratoma. Middle mediastinal masses include lymphoma, metastatic disease, granulomatous diseases, and vascular masses/enlargments. Posterior mediastinal masses include diseases of neural tissue or esophageal origin, such as neurofibroma and schwannoma or esophageal leiomyoma and carcinoma.
Thymic neoplasms include both thymomas and thymic carcinomas. They are staged based on the extension of the primary tumor and involvement of surrounding tissue. Clinically, patients present as asymptomatic, as a paraneoplastic condition, or with symptoms based on the size of the tumor. Thoracic symptoms include chest pain, shortness of breath, or cough. The most common paraneoplastic disorder is myasthenia gravis which is seen in about 30-40% of cases. In patients considered to be acceptable candidates, surgical excision is the firstline treatment for resectable disease (stages I and II). Unresectable disease (stages II and IV) can be treated with neoadjuvant or palliative chemotherapy.
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