<s>[INST] context: - Given clinical features suggests the diagnosis of Myasthenia gravis. Myasthenia gravis -Acquired autoimmune disease characterized by abnormal muscular fatigability, caused by circulating antibodies to acetylcholine receptor at myoneural junction . -Manifests with ptosis (drooping eyelids) or diplopia (double vision) because of weakness in extraocular muscles. -Pattern of weakness is distinctly different from most primary myopathic diseases, in which there is relative sparing of facial & extraocular muscles. -Repetitive firing of muscles makes weakness more severe, whereas cholinesterase inhibitors improve strength markedly - diagnostically useful. - In 2/3rd of patients, thymic hyperplasia is closely associated with myasthenia gravis & 15% have thymoma. - Conversely, 1/3rd to 1/2 of patients with thymoma develop myasthenia gravis. - Thymectomy is often an effective treatment for these patients. - Cholinesterase inhibitors, immunosuppression, plasmapheresis can also be used in treatment. [/INST] question: A 55-year-old man complains of severe muscle weakness and drooping eyelids. He states that his symptoms worsen with repetitive movements but then resolve after a sho rest. A chest X-ray reveals an anterior mediastinal mass. A biopsy of this mass would most likely reveal which of the following pathologic changes? | options: A: B-cell lymphoma B: Hodgkin lymphoma C: Metastatic carcinoma D: Thymic hyperplasia | answer: D </s>