Paraneoplastic Encephalitis Associated with Thymoma: A Case Report
A 42-year-old woman presented with a history of 15 days of short-term memory loss. She complained of generalized weakness and voice changes over the previous 3 months. On physical examination, she had mild bilateral ptosis. Chest X-ray revealed a right hilar mass and chest computed tomography showed a 5 cm anterior mediastinal mass consistent with a thymoma ().\nOn hospital day 2, she suddenly exhibited personality changes and severe agitation, which evolved into a drowsy mental status. Arterial blood gas analysis demonstrated hypoxemia (PaO2, 68.4 mmHg), hypercapnea (58.3 mmHg), and respiratory acidosis (pH, 7.187), prompting orotracheal intubation and ventilator care. Brain magnetic resonance imaging (MRI) showed multifocal high intensity signals in the cerebral cortex including the limbic area on T2 flare images (). Diffuse delta background activity and moderate diffuse cerebral dysfunction were observed on electroencephalography (EEG). In serologic tests, serum acetylcholine receptor (AchR) antibody titer (11.189 nmol/L) was elevated, but antineuronal nuclear antibody (Hu/Ri) and Purkinje cell antibody (Yo) were negative. Considering these findings, we thought that she had myasthenia gravis and paraneoplastic encephalitis associated with a thymoma.\nThymectomy was recommended, but due to the patient's drowsy mental status, it was difficult to obtain consent for the surgery from her guardians. Ultimately, on hospital day 8, she underwent a thymectomy, the pathology of which revealed a thymoma, type B1. The thymoma had invaded the pericardium and pericardial fat tissues with metastasis to the right diaphragm. Despite the thymectomy, the patient's mental status and odd behavior still did not improve. On postoperative day 10, follow-up brain MRI was performed, but the previous high intensity lesion still remained. Thereafter, her mental status and abnormal behavior gradually improved. On postoperative day 90, her cognitive status had nearly fully recovered and brain MRI on postoperative day 96 showed that the previous lesions had disappeared (). On postoperative day 106, the patient was discharged without complications. Because the thymoma pathologically invaded adjacent tissues, we recommended additional radiotherapy. However, she refused further treatment. At 2 years after thymectomy, she has had no specific symptoms, but the AchR antibody titer is still high (13.483 nmol/L). She takes only 180 mg per day of pyridostigmine from our outpatient clinic.